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A selection of interesting papers that were published inthe two months before our press date in major journalsmost likely to report significant results in immunology.

Current Opinion in Immunology 2001, 13:255–264

Contents (chosen by)

255 Antigen processing and recognition (Elliott)256 Innate immunity (Bonneville)257 Lymphocyte development (Kruisbeek and van Halem)258 Tumour immunology (Walker)259 Lymphocyte activation and effector functions (Casolaro)259 Immunity to infection (Glaichenhaus and Vyakarnam)261 Immunogenetics (Casanova)262 Immunotherapy (Liu)262 Allergy and hypersensitivity (Akdis)263 Autoimmunity (Green)

• of special interest•• of outstanding interest

Antigen processing and recognitionSelected by Tim ElliottUniversity of Southampton, Southampton, UK

A role for calnexin in the assembly of the MHC class I load-ing complex in the endoplasmic reticulum. Diedrich G,Bangia N, Pan M, Cresswell P: J Immunol 2001,166:1703-1709.• Significance: The way in which MHC class I molecules areassembled inside the endoplasmic reticulum (ER) with antigenicpeptides is not fully understood. Several co-factors are involvedin this, including the transporter associated with antigen presentation (TAP), tapasin, the ER chaperone molecules cal-nexin and calreticulin, and the thio-reductase ERp57. How theywork together to make a stable antigen-presenting moleculemay be important for understanding immunological phenomenasuch as immunodominance. This paper elucidates early eventsin the stepwise assembly of the MHC class I loading complex.Findings: Using cell line that lacks β2 microglobulin (Daudi),the authors were able to identify a pre-loading complex whichcontains the TAP hetrodimer, tapasin, ERp57 and calnexin butno MHC class I heavy chain. The calnexin−ERp57 complexbound directly to tapasin in this assembly. When β2 microglob-ulin was introduced into the cell line, much less of this complexwas observed and instead calreticulin was found associatedwith TAP, tapasin and ERp57. The complexes now includedMHC class I molecules. In the pre-loading complex, calnexininteracted with the transmembrane domain of tapasin since aninteraction was seen with a tapasin construct lacking theamino-terminal, luminal domain but not with a soluble form.Pulse/chase analysis in normal cells shows that TAP andtapasin assembled co-translationally and that ERp57 boundslightly later along with MHC class I. The authors therefore propose that the TAP−tapasin complex forms first, then bindscalnexin and ERp57, and that calnexin is then displaced fromthis pre-loading complex by newly assembled MHC class I molecules bound to calreticulin.

Quantitative and qualitative influences of tapasin on theclass I peptide repertoire. Purcel AW, Gorman JJ,Garcia-Peydro M, Paradela A, Borrows SR, Talbo GH,Laham N, Peh CA, Reynolds EC, Jose Lopez de Castro A,McCluskey J: J Immunol 2001, 166:1016-1027.• Significance: The human HLA molecule B*2705 (B27) isunusual in that its expression and antigen-presenting functionappear to be relatively tapasin independent. This manuscriptadds to our understanding of tapasin function by demonstrat-ing both quantitative and qualitative differences in the repertoireof endogenous ligands presented by this allele in the absenceof tapsin. These data may be relevant to the strong associationbetween B27 and ankylosing spondylitis by suggesting that anyimpairment of tapasin function in a B27-expressing individualcould lead to an increase in the presentation of poorly tolerisedself peptides. This could lead to a potential antigenic stimulusfor autoreactive T cells.Findings: The authors were able to immunopurify an equivalentamount of B27 molecules from tapasin competent and tapasindeficient cells. However, after extensive washing of theimmunopurified molecules, around five-times less peptide wasrecovered from B27 molecules isolated from tapasin negativecells. Mass-spectrometric analysis of these peptides revealedthat very similar repertoires were bound to each population ofB27 although on closer inspection there were some differ-ences. For example, some sequences appeared to berecovered only from cells that lacked tapasin, others appearedto be tapasin specific. Among the former was a peptide derivedfrom the B27 heavy chain itself. Interestingly, this peptide(residues167−179) has previously been suggested as an arthri-togenic peptide. Overall no differences in the affinity of bindingof tapasin dependent and tapasin independent peptides wereobserved. Alloreactive T cells raised to tapasin positive andtapasin negative B27-expressing stimulators could also dis-criminate between B27 molecules expressed on tapasinpositive or tapasin negative cell lines.

Protective immunity to UV radiation-induced skin tumoursinduced by skin grafts and epidermal cells. Sluyer R,Yuen KS, Halliday GM: Immunol Cell Biol 2001, 79:29-34.• Significance: This study develops previous work in a mousemodel of UV-radiation-induced skin tumours, showing that skingrafts overlying a tumour can confer protection to a naïve animal subsequently challenged with the same tumour.Findings: The authors firstly established that skin fromtumour-bearing mice, that was previously overlying the tumour, canbe grafted onto naïve mice and protect them from a subsequenttumour challenge (2 × 106 cells) 21 days later. This protection wasnot observed when normal skin was incubated with tumour extract(TE) at 4oC overnight. They subsequently showed that the purifiedepidermal cells incubated with TE (30 minutes at 37oC) could onlyprovide partial protection to a lower dose of tumour cells (1 × 105

cells) and not to the original tumour load.

Clonal anergy induced in a CD8+ hapten-specific cytoxicT-cell clone by an altered hapten-peptide ligand. Preckel T,Hellwig S, Pflugfelder U, Lappin MB, Weltzien HU:Immunology 2001, 102:8-14.

ImmunologyPaper alert

• Significance: T cell anergy is thought to be a mechanism ofmediating peripheral tolerance in vivo. Previous studies havereported T cell anergy resulting from T cell stimulation by inap-propriate antigen-presenting cells or mediated via alteredpeptide ligands. This study identifies an altered hapten−peptideligand that induces anergy in a CD8+ clone. As hapten-specificT cells are thought to play a role in allergic disease caused bychemicals and drugs, such modified ligands are attractive forinvestigating and modulating potential pathogenic mechanisms.Findings: These authors continue previous work using a modelhapten−peptide, TNP−M4L (peptide sequence SMQK*FGEL),and a CD8+ cytotoxic T lymphocyte (CTL) clone (E6) thatrecognises it. A second ligand, TNP−O4 (SIIK*FEKL), is alsorecognised by this clone, which can be activated to lyse targetcells but not to proliferate. In this study, the authors show thatan altered hapten−peptide ligand, DNP−O4, but not DNP−M4Linhibits lysis of TNP−M4L-pulsed target cells in a cold targetinhibition assay. This inhibition of target cell lysis required thatthe altered hapten−peptide ligand and unaltered hapten−pep-tide ligand be expressed on the same target cell. However, theyfurther show that pre-exposing the E6 clone to the DNP−O4altered hapten−peptide ligand prevented a subsequentresponse to the TNP−M4L target cells and induced a state ofchronic anergy. This state of anergy could be reversed by re-stimulating the E6 CTL clone with TNP−M4L in the presence ofIL-2 or IL-12 plus IL-18. Thus, altered hapten−peptide ligandscan have independent effects upon a CTL clone, inducing bothanergy and an anergy independent inhibition of target cytolysis.

The immunogenicity of a new human minor histocompati-bility antigen results from differential antigen processing.Brickner AG, Warren EH, Caldwell A, Akatsuka Y, Golovina TN,Zarling AL, Shabanowitz J, Eisenlohr LC, Hunt DF,Engelhard VH, Riddell SR: J Exp Med 2001, 193:195-205.• Significance: This paper identifies a novel minor histocom-patibility antigen (mHAg) by direct sequencing of antigenicpeptides. The authors show that this sequence is polymorphicbut that differences in T cell recognition arise from differencesin the processing of these peptide antigens rather than differ-ential recognition by the TCR.Findings: Using a cytotoxic T cell clone known to recognise anmHAg in order to identify biologically active fractions, theauthors fractionated peptides eluted from an HLA-A*0201+

mHAg+ cell line. After three rounds of HPLC fractionation, can-didate peptide antigens were identified and sequenced bymass spectrometry. The sequence RTLDKVLEV (R1V9) was apotent sensitiser of target cells and was derived from a gene ofunknown function on chromosome 9. The gene was found to bepolymorphic, encoding two other variants (PTLDKVLEV [P1V9]and PTLDKVLEL) in the population. Cells expressing the lattertwo sequences were not recognised by the T cell clone.However, the clone did recognise PTLDKVLEV almost as effi-ciently as the R1V9 allele (300 pM rather than 20 pMhalf-maximum lysis). This suggested that the P1V9 allele wasprocessed differently, a notion that was borne out by the factthat whereas the transfected cytosolic minigene was unable tosensitise target cells, a minigene construct that was co-transla-tionally translocated into the ER by a leader sequence waseffectively recognised. The authors go on to show that theP1V9 peptide is translocated by the TAP transporter less effi-ciently than the R1V9 peptide, as were P1V9 peptidescontaining one or five additional natural amino-terminal flankingamino acids.

Innate immunitySelected by Marc BonnevilleInstitut de Biologie, Nantes, France

Involvement of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in surveillance of tumor metastasisby liver natural killer cells. Takeda K, Hayakawa Y, Smyth MJ,Kayagaki N, Kakuta S, Iwakura Y, Yagita H, Okumura K:Nat Med 2001, 7:94-100.• Significance: This study describes a novel mechanism oftumor surveillance mediated by NK cells, which could explainthe long-known antitumor effects of IFN-γ. It also provides thefirst evidence for a role of TRAIL as a tumor suppressor in vivo.Findings: Although TRAIL has been shown to be involved inapoptosis of various cells in vitro, its physiological role remainsunknown. This study shows that TRAIL is constitutivelyexpressed by liver-derived NK cells but not by NK-T or conven-tional T cells. TRAIL not only is responsible for NK-mediatedcytotoxicity against several tumor cells in vitro but also is involvedin the control of liver metastases of several TRAIL-sensitive tumorcell lines, as suggested by the in vivo effect of neutralizing mon-oclonal antibody against TRAIL. The antimetastatic effect ofTRAIL is not observed in NK-cell-deficient mice or IFN-γ-deficientmice, which lack TRAIL+ NK cells.

Downregulation of bactericidal peptides in enteric infec-tions: a novel immune escape mechanism with bacterialDNA as a potential regulator. Islam D, Bandholz L, Nilsson J,Wigzell H, Christenson B, Agerberth B, Gudmundsson GH:Nat Med 2001, 7:180-185.• Significance: This study describes a novel pathogenic mech-anism used by bacteria that cause diarrhea; the mechanismrelies on inhibition of epithelial innate defense by bacterial DNA.Findings: Antibacterial peptides are important innate immuneeffectors produced by epithelial cells, which presumably play arole of first line of defence against infections. Analyses of biop-sies from patients with dysenteries and of epithelial ormonocytic cells infected in vitro indicate that, early in infectionsby Shigella spp. or other bacteria causing watery diarrhea,expression of the antibacterial peptides LL-37 and β-defensin-1is downmodulated. This effect is still observed after in vitroincubation of cells with bacterial lysate treated with proteasesbut not with lysates treated with DNAses. Furthermore, down-modulation of LL-37 is achieved by incubating cells withpurified bacterial plasmids, thus suggesting a major role forbacterial DNA in antibacterial peptide downregulation.

Induction of direct antimicrobial activity through mam-malian Toll-like receptors. Thoma-Uszynski S, Stenger S,Takeuchi O, Ochoa MT, Engele M, Sieling PA, Barnes PF,Röllinghof M, Bölcskei PL, Wagner M et al.: Science 2001,291:1544-1547.• Significance: Toll-like receptors (TLRs) represent a family ofhighly conserved molecules that activate adaptive immuneresponses by inducing the production of various proinflamma-tory cytokines. This study shows for the first time that TLRs canalso directly activate antimicrobial effector pathways in innateimmune cells.Findings: Incubation of macrophages with bacterial lipoprotein,a microbial ligand for TLR2, leads to direct killing of intracellu-lar Mycobacterium tuberculosis. This antibacterial effect isblocked by monoclonal antibodies directed against TLR2 and isno longer observed in TLR2-deficient cells. Whereas in murinemacrophages TLR2-mediated inhibition of bacterial replication

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depends on release of nitric oxide (NO), it is NO-independentin human monocytes and alveolar macrophages.

ULBPs, novel MHC class-I related molecules bind to CMVglycoprotein UL16 and stimulate NK cytotoxicity throughthe NKG2D receptor. Cosman D, Müllberg J, Sutherland CL,Chin W, Armitage R, Fanslow W, Kubin M, Chalupny NJ:Immunity 2001, 14:123-133.• Significance: This study identifies a new family of receptorsthat are broadly expressed on normal and transformed cells ofhemopoietic and epithelial origin and that are involved in NKcell activation by tumors and could contribute to NK immuneevasion by human cytomegalovirus (HCMV).Findings: A soluble form of UL16, an HCMV-encoded glyco-protein, is shown to bind to two members of a novel family ofmolecules called UL-binding proteins (ULBPs) and to the pre-viously described MHC class I homolog, MICB. Both ULBPand MIC proteins bind to NKG2D, an activating receptor foundon NK cells, γδ T cells and CD8+ T cells. Expression of ULBPon NK-resistant target cells confers susceptibility to NK lysis,and recombinant soluble forms of ULBP induce cytokine andchemokine production by NK cells. ULBP-mediated activationof NK cells is blocked by soluble UL16, thus suggesting a pos-sible evasion mechanism developed by HCMV to counteractNK cell attack.

Lymphocyte developmentSelected by Ada Kruisbeek and Marie Anne van HalemThe Netherlands Cancer Institute, Amsterdam, The Netherlands

Id3 inhibits B lymphocyte progenitor growth and survival inresponse to TGF-ββ. Kee BL, Rivera RR, Murre C: Nat Immunol2001, 2:242-247.• Significance: The basic helix-loop-helix (bHLH) transcriptionfactors (E proteins) have essential roles in cell fate and differ-entiation decisions in many cell types, including lymphocytes.Mice lacking the E2A gene products E12 and E47 fail to gen-erate B cells but it is largely unknown in which processes theE proteins participate and how their activity is regulated. Thepresent study suggests that transforming growth factor β(TGF-β) mediates its inhibitory effects on lymphocyte survivaland growth through induction of Id3, an E protein antagonist.Findings: First, it is shown that ectopic expression of Id3 in primary B lymphocyte progenitors (BLPs) induces caspase-dependent apoptosis. Furthermore, TGF-β induces Id3 mRNAand protein in BLPs (but induces no Id1 or Id4 and little Id2) andits growth inhibitory effect on BLPs is delayed in absence of Id3.Finally, activation of Smad transcription factors by TGF-β isrequired for the induction of Id3. Together, the data show that Id3is a target of TGF-β induced signaling in B lymphocytes.

Regulation of the helix-loop-helix proteins, E2A and Id3, bythe Ras-ERK MAPK cascade. Bain G, Cravatt CB,Loomans C, Alberola-Ila J, Hedrick SM, Murre C: Nat Immunol2001; 2:165-171.• Significance: Just like B lymphopoiesis (see Kee et al.,above), also T cell development is dependent on the activity ofbHLH proteins. Specifically, thymocytes in HEB-null mutantmice are blocked at the immature single-positive stage and thy-mocyte development in E2A-deficient mice is blocked at anearly double-negative stage. Also, thymocyte selection at thedouble-positive (DP) stage is defective in the absence of Id3,one of the dominant negative inhibitors of E protein activity.Given these observations, it is important to understand how

E protein activity is regulated by external signals. Here, Bainand colleagues suggest that TCR-triggered activation of theLck/Ras/ERK cascade results in Id3 activation.Findings: TCR-mediated stimulation of DP thymocytes resultsin reduction of E-box binding activity and in induction of Id3.This induction is dependent on activation of components in theERK-MAPK pathway, and constitutively active forms of Lck andMEK1 induce Id3 in a DP cell line. Finally, the ERK-mediatedactivation of Id3 is shown to require de novo proteins synthesisand can be mimicked by ectopic Egr1 expression. The gene forEgr1 is one of the immediate early growth response genesinduced by TCR ligation, is induced before Id3 and is alsodependent on Ras. The main observation of this study is thatthe TCR-triggered ERK-MAPK pathway regulates E-proteinbinding activity at least in part by regulating Id3.

IκκB kinase αα is essential for mature B cell development andfunction. Kaisho T, Takeda K, Tsujimura T, Kawai T, Nomura F,Terada N, Akira S: J Exp Med 2001, 193:417-426.• Significance: The nuclear factor (NF)-κB family of transcrip-tion factors is, in resting cells, retained in the cytoplasm by IκBproteins. Upon phosphorylation of IκBs by IκB kinases (IKKs),the IκBs are degraded and NF-κBs are activated. All NF-κBsare expressed in B cells but, since IKKα- and IKKβ-deficientmice die during early neonatal life, it is unclear whether IKKα orIKKβ are involved in NF-κB activation in B lymphocytes. Toaddress this issue, chimeric mice are established with fetal livercells from IKKα-deficient mice and a critical role for IKKα inB lymphopoiesis is established.Findings: Mice lacking T and B cells because of recombinationactivating gene (RAG)-2 deficiency were reconstituted withfetal liver from IKKα-deficient mice. Reconstituted mice havenormal T cell development but a severe decrease in matureB cells in peripheral blood, spleen and bone marrow. The pop-ulation size of pro-B, pre-B and immature B cells, however, isunaffected. IKKα-deficient B cells also exhibit impaired NF-κBactivation and significantly augmented apoptotic death undervarious conditions, consistent with the role of NF-κB in regulat-ing anti-apoptotic genes. Also, B cell function is impaired (asevidenced by decreased basal levels of immunoglobulin andimpaired antigen-specific responses) and there is poor germi-nal center formation. IKKα thus emerges as a critical regulatorof B cell survival and functional development.

Loss of precursor B cell expansion but not allelic exclusionin VpreB1/VpreB2 double-deficient mice. Mundt C,Licence S, Shimizu T, Melchers F, Mårtensson IL: J Exp Med2001, 193:435-445.• Significance: Once pre-B cells have successfully produceda µH chain, it associates with surrogate light (SL) chain to forma pre-BCR complex. This complex mediates crucial survival,proliferation and differentiation signals in pre-B cells and estab-lishes allelic exclusion at the IgH chain alleles. The SL chain iscomposed of λ5 and VpreB proteins, and mice have two VpreBgenes, VpreB1 and VpreB2. Mice lacking VpreB1 have only amild defect in exit from the pre-B cell stage and use a SL com-posed of VpreB2 and λ5. To better understand the functionalrelevance of VpreB genes, the present study now examinesmice lacking both VpreB1 and VpreB2.Findings: B cell development is impaired at the transition fromthe pre-BI to the pre-BII stage in mice lacking both VpreB1and VpreB2. This results in a severe reduction in pre-BII cells,immature B cells and mature B cells, and appears primarily

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due to a lack of proliferative expansion of pre-BII cells orimpairment of progression through the pre-BII stage.Surprisingly, allelic exclusion at the µH chain locus still occursin mice without VpreB1 or VpreB2. Since this phenotype isreminiscent of that in λ5-deficient mice, the authors speculatethat IgL chains take the place of the SL chain in mediating thesignals for allelic exclusion.

Allelic exclusion and differentiation by protein kinase C-mediated signals in immature thymocytes. Michie AM,Soh J-W, Hawley RG, Weinstein IB, Zúñiga-Pflücker JC:Proc Natl Acad Sci USA 2001, 98:609-614.• Significance: How is signaling specificity achieved by thepre-TCR? Like the pre-BCR in pre-B cells (see Mundt et al.,above) the pre-TCR controls many functions in pre-T cells,including survival, proliferation, differentiation and allelic exclu-sion at the TCRβ locus. All pre-TCR driven selection events aredependent on SLP-76 (a critical upstream scaffold protein forseveral adaptors) but little is known about how pre-TCR signalsbifurcate thereafter. Earlier studies suggested that the signalsfor allelic exclusion bifurcate upstream of Ras activation, sincethe Ras/MAPK pathway is required for survival and proliferationand transition to the DP stage but appears unable to induceTCRβ allelic exclusion. The present study implicates PKC mediated signals in allelic exclusion.Findings: Constitutively active PKC can bypass the require-ment for pre-TCRs in thymocyte differentiation and providesboth differentiative and proliferative signals. Furthermore, pre-TCR complex formation induces PKC activation and PKCactivation is necessary for induction of differentiation past thepre-T cell stage. Most importantly, PKC-derived signals enforceallelic exclusion at the TCRβ locus in developing thymocytes.PKC signals are thus critical mediators of pre-TCR signal spec-ification and can be positioned at the branch point wheresignals leading to proliferation and differentiation diverge fromthose regulating allelic exclusion.

Tumour immunologySelected by Paul R WalkerUniversity Hospital Geneva, Geneva, Switzerland

Antigen-specific inhibition of effector T cell function inhumans after injection of immature dendritic cells.Dhodapkar MV, Steinman RM, Krasovsky J, Munz C,Bhardwaj N: J Exp Med 2001, 193:233-238.• Significance: Dendritic cells (DCs) are considered to bepotent adjuvants that may be valuable for use in cancer vac-cines. However, their maturation status is known to influencetheir capacity to stimulate T cell immune responses, althoughthis is based principally on in vitro data. In this report, an in vivoinhibitory function of immature DCs is demonstrated for the firsttime in humans. Thus, rather than simply being inefficientimmunostimulators, immature DCs may actively lead to thedownregulation of immune responses — potentially useful fortreating autoimmunity, but not the effect usually required fortumour immunotherapy. Findings: Four normal healthy individuals were immunised withautologous DCs pulsed with keyhole limpet haemocyanin(KLH) and/or HLA-A*0201-restricted influenza matrix peptide(MP). Immune responses were assessed, ex vivo or afterin vitro restimulation, using antigen-specific IFN-γ, IL-4 andIL-10 ELISPOTS, HLA-A*A0201−MP tetramer binding assaysor proliferation in response to KLH. As expected, MP-specificCD8+ T cells were detected in pre-immune blood samples but,

surprisingly, immature-DC immunisation resulted in a significantreduction in IFN-γ-secreting cells and an augmentation inIL-10-secreting cells. Furthermore, when T cells were restimu-lated in vitro, cytotoxicity and IFN-γ release were markedlyreduced in post-immunisation T cells, despite enhanced expan-sion of MP specific (tetramer+) CD8+ T cells, compared withpre-immunisation T cells. Unfortunately, only CD4+ T cellresponses (to KLH) could be compared with the individualsreceiving mature DCs; there were barely detectable responsesafter immature-DC immunisation whereas IFN-γ-secreting cellsshowing high in vitro proliferation were detected aftermature-DC immunisation.

Diverse expansion potential and heterogeneous avidity intumor-associated antigen-specific T lymphocytes from pri-mary melanoma patients. Palermo B, Campanelli R,Mantovani S, Lantelme E, Manganoni AM, Carella G,Da Prada G-A, Robustelli della Cuna G, Romagne F, Gauthier Let al.: Eur J Immunol 2001, 31:412-420.• Significance: MHC−peptide tetramers are powerful tools forthe analysis of T cells specific for tumour associated antigens.An important question is whether tetramer staining intensity canbe predictive of T cell function. This paper directly addressesthis issue, testing the critical parameter of tumour cell lysis,which was not always achieved even by tetramerbright clones.Findings: Peripheral blood from nonmetastatic-melanomapatients was analysed for the presence of Melan-A-, tyrosinase,MAGE-3- or gp100-specific CD8+ T cells, on the basis ofMHC−peptide tetramer staining. Low levels of Melan-A- andtyrosinase-specific cells were detected in some patients, whichfor Melan-A-tetramer+ cells could generally be enriched and expanded after in vitro restimulation, whereastyrosinase-tetramer+ cells were refractory to expansion. Avidityof Melan-A-specific clones was assessed by peptide titrationon T2 cells; a wide range of values was detected but only highavidity clones efficiently killed melanoma cell lines. However,this efficient antitumour function (in vitro) was not correlatedwith TCR affinity as assessed by tetramer binding. Theseresults are encouraging in that high avidity tumour specificclones are present in patients and can be expanded in vitro butit appears that we do not as yet have a unique phenotypicmarker for their monitoring.

Targeting of lymphotoxin-αα to the tumor elicits an efficientimmune response associated with induction of peripherallymphoid-like tissue. Schrama D, thor Straten P, Fischer WH,McLellan AD, Bröcker E-B, Reisfeld RA, Becker JC: Immunity2001, 14:111-121.• Significance: The capacity of tumour-specific T cells toundergo clonal expansion and to home to the tumour site willundoubtedly influence their overall antitumour function.However, it is not clear whether T cell priming in tumour-drain-ing lymph nodes always results in efficient antitumourresponses. This paper describes and assesses the conse-quences of T cell priming and expansion in vaccination-inducedperitumoral lymphoid-like tissue.Findings: Schrama et al. used a fusion protein, comprisingtumour-specific antibody with lymphotoxin-α, as a therapeuticimmunocytokine for treatment of a modified B16 murinemelanoma; tumour regression and prolonged host survival wereachieved in a majority of mice. Peritumoral lymphoid tissue wasgenerated in treated mice; the tissue exhibited lymph-node-likefeatures, including high endothelial venules. This tissue

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appeared to be functional since there was an accumulation ofCD62L+ T cells that underwent clonal expansion and includedmany tumour-antigen-specific, functional, cytotoxic T lympho-cytes (which were not detectable in draining lymph nodes).Such peritumoral lymphoid neogenesis may facilitate T cell prim-ing due to high local tumour-antigen concentration. It will beinteresting to determine whether the potential benefits of tumourproximity are retained for human and other murine tumoursknown to produce high levels of immunosuppressive factors.

Lymphocyte activation and effector functionsSelected by Vincenzo CasolaroThe Johns Hopkins School of Medicine, Baltimore, MD, USA

A critical role for NF-κκB in Gata3 expression and TH2 dif-ferentiation in allergic airway inflammation. Das J,Chen C-H, Yang L, Cohn L, Ray P, Ray A: Nat Immunol 2001,2:45-50.• Significance: NF-κB, a diverse group of structurally related,dimeric transcription factors, regulates the expression of sev-eral genes in immune and inflammatory cells. In particular, theactivation and nuclear translocation of p65−p50 or c-Rel−p50dimers has been associated with critical effector functions inT helper cells activated via TCR and CD28 engagement.Recent studies by Ray and coworkers have documented aselective defect in Th2-driven airway inflammatory responses inmice lacking the NF-κB subunit p50 (p50–/–). This study by thesame group represents a due attempt to understand the natureof this defect and, inherently, to define the specific role ofNF-κB in T helper cell differentiation and function.Findings: p50−/− mice exhibit reduced antigen-induced airwayeosinophilia and IL-4, IL-5 and IL-13 levels, consistent withreduced Th2 cell recruitment and/or function. To understandwhether this phenotype had to be primarily accounted for by anintrinsic versus an extrinsic defect in T helper cells, in-vitro-gener-ated antigen-specific Th2 cells were adoptively transferred intosyngeneic wild-type or p50−/− mice prior to airway antigen chal-lenge. Irrespective of the genetic background, recipient miceconsistently displayed intense airway eosinophilia, indicating thatthe primary defect in p50–/– animals is in the ability to generate,rather than recruit, Th2 cells. In subsequent experiments, isolatedCD4+ T cells from p50–/– mice were found to express lower lev-els of the Th2 cytokine gene activator, GATA-3, following exposureto TCR- and CD28-delivered signals under Th2-polarizing condi-tions. Although this could explain coordinately reduced expressionof IL-4, IL-5 and IL-13 in p50−/− mice, it also revealed a novelNF-κB-dependent pathway of GATA-3 gene activation in differen-tiating T helper cells. To further substantiate this finding, theauthors looked at the effect of in vitro incubation with a peptideantagonist (SN50) of p50 nuclear translocation on GATA-3expression and Th2 cytokine gene activation. SN50 inhibited bothparameters in differentiating T helper cells, but not in fully commit-ted Th2 cells, suggesting a critical role of NF-κB in thedevelopmental processes regulating coordinate expression of Th2cytokine genes. As p50 is a component of NF-κB dimers thathave diverse functions in cytokine gene regulation, additional stud-ies are awaited to further define the relative contribution of otherNF-κB family members to differential activation of cytokine genesin developing T helper cells.

An instructive component in T helper cell type 2 (Th2)development mediated by GATA-3. Farrar JD, Ouyang W,Löhning M, Assenmacher M, Radbruch A, Kanagawa O,Murphy KM: J Exp Med 2001, 193:643-649.

• Significance: The differentiation of naïve T helper cells intopolarized effectors is thought to be ‘instructed’ by Th-exoge-nous factors, such as antigen density, the nature and strengthof costimulatory signals and the cytokine microenvironment.However, according to an emerging model, T helper cell primary commitment is independent of these signals, andpolarizing signals, for example IL-4 or IL-12, would only act byfavoring the ‘selective’ outgrowth of stochastically generatedlineages. This study by Murphy and collaborators tries todefine the relative weight of the instructive and selective com-ponents of T helper cell differentiation using a novel approachto directly monitor T helper fate decision at both the clonal andpopulation levels.Findings: When naïve T helper cells from normal mice, orfrom animals lacking the IL-4 downstream effector STAT6(STAT6–/–), were activated under neutral conditions (i.e. inthe absence of polarizing signals), a persistent population ofcells was still observed that preferentially produced IFN-γ orIL-4, consistent with stochastic activation of either gene.According to the selective model of Th1/Th2 cell commit-ment, these phenotypes would be permanent; subsequentexposure to polarizing signals would only affect their expan-sion but cause no further modification. To elucidate thispoint, the authors separated IL-4-producing and -nonproduc-ing cells in these preparations, by a cellular affinity matrix, toanalyze their phenotype and function under Th2-polarizingconditions. Exposure of IL-4− cells to exogenous IL-4 wassufficient to redirect them to an IL-4-producing, Th2-like phe-notype. Consistent with the instructive model of Th2 cellgeneration, this effect of IL-4 was not observed in cells fromSTAT6−/− mice, stressing the need for an intact IL-4 signalingpathway. Ectopic expression of the coordinate activator ofTh2 cytokine genes, GATA-3, by means of a high-efficiencyretroviral vector, was sufficient to reproduce the instructiveeffect of exogenous IL-4 on IL-4− T helper cells and tobypass the specific requirement for STAT6 signaling in thisprocess. Thus, whereas the initial, low-frequency productionof IL-4 is consistent with stochastic activation via bothSTAT6-dependent and -independent pathways, the develop-ment of a stable, polarized Th2 phenotype appears todepend on instructive signals, at least in part provided byIL-4-induced STAT6 and GATA-3.

Immunity to infectionSelected by Nicolas GlaichenhausInstitut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France

Recognition of haemagglutinins on virus-infected cells byNKp46 activates lysis by human NK cells. Mandelboim O,Lieberman N, Lev M, Paul L, Arnon TI, Bushkin Y, Davis DM,Strominger JL, Yewdell JW, Porgador A: Nature 2001,409:1055-1060.•• Significance: NK cells recognize virus-infected and tumorcells through both inhibitory and activating receptors.Whereas inhibitory receptors interact with MHC class I molecules, the ligands of activating receptors remained to beidentified. In this paper, the authors show that the main acti-vating receptor of human NK cells, NKp46, binds to both thehaemagglutinin (HA) of influenza virus and the haemagglu-tinin-neuramidinase (HN) of parainfluenza or Sendai virus.Although it should be kept in mind that some NK cells canlyse target cells in an NKp46-independent manner, these find-ings indicate how NKp46-expressing NK cells may recognizeinfected target cells.

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Findings: Using a fusion molecule in which the extracellulardomain of NKp46 was fused to the Fc portion of immunoglob-ulin (Ig), the authors identified the HN glycoprotein of Sendaivirus as one of the ligands for NKp46. Thus, cells transfectedwith the HN gene were stained more brightly with NKp46−Igmolecules and were killed more efficiently by NKp46-express-ing NK cells than nontransfected, control cells. The authorsalso found that purified HA from influenza virus bound to periph-eral blood NK cells and that this binding was blocked byNKp46−Ig. Further experiments suggested that both HA andHN recognized sialylated oligosaccharides on NKp46.

Mechanism of measles virus-induced suppression ofinflammatory immune response. Larie JC, Kehren J,Trescol-Biémont MC, Evlashev A, Valentin H, Walzer T,Tedone R, Loveland B, Nicolas JF, Rabourdin-Combes C,Horvat B: Immunity 2001, 14:69-79.•• Significance: Although both virulent and attenuatedmeasles virus (MV) have been reported to induce immunosup-pression, the mechanisms that are responsible for thisphenomenon remained poorly understood. In this paper, theauthors found that immunosuppression did not require viralreplication but could be induced by purified MV proteins — theMV nucleoprotein (NP) and the envelope hemagglutinin (H) andfusion (F) glycoproteins. Beside providing important informationon the mechanisms that are responsible for MV-inducedimmunosuppression, this work may have important implicationsfor the development of a new generation of MV vaccines thatare deprived of immunosuppressive activity.Findings: In this paper, the authors first showed that MV particlesinhibited both contact hypersensitivity (CHS) and delayed-typehypersensitivity (DTH) responses upon intraperitoneal injectioninto mice. Using both recombinant MV and purified MV proteins,the authors demonstrated that at least two pathways were respon-sible for MV-induced immunosuppression: one required theinteraction between MV NP and its cellular receptor, FcγR,whereas the other implicated the MV envelope proteins H and Fand their receptor on human cells, CD46.

T cell release of granulysin contributes to host defense inleprosy. Ochoa MT, Stenger S, Sieling PA, Thoma-Uszynski S,Sabet S, Cho S, Krensky AM, Rollinghoff M, Nunes Sarno E,Burdick AE et al.: Nat Med 2001, 7:174-179.• Significance: Leprosy, caused by the intracellular bacteriumMycobacterium leprae, is a major social burden on developingcountries. Clinical manifestations of leprosy correlate with thelevel of cell-mediated immunity (CMI) to the bacteria. Thus,patients who mount a strong CMI to M. leprae exhibit only rarelesions containing small numbers of bacteria (tuberculoid lep-rosy). In contrast, individuals who mount a weak CMI showdisseminated lesions with high numbers of bacteria (leproma-tous leprosy). The present study demonstrates a correlationbetween the absence in the lesions of CD4+ T cells express-ing the antimicrobial protein granulysin and the severity of theclinical symptoms.Findings: By immunohistochemistry and confocal microscopy,the authors show that the numbers of T cells that express gran-ulysin are reduced in patients with lepromatous leprosy ascompared with those with tuberculoid leprosy. In contrast, thenumbers of T cells expressing perforin are identical in both typesof patients. Unexpectedly, the T cells that express granulysin andexhibit cytotoxic activities against mycobacteria-infected targetsin vitro belong to the CD4+ subset.

Downregulation of bactericidal peptides in enteric infec-tions: a novel immune escape mechanism with bacterialDNA as a potential regulator. Islam D, Bandholtz L, Nilsson J,Wigzell H, Christensson B, Agerberth B, Gudmundsson G:Nat Med 2001, 7:180-185.•• Significance: Antibacterial peptides are major actors of thedefense against microbial pathogens at epithelial surfaces. Inthis study, the authors show that the expression of two importanthuman bactericidal peptides is dramatically reduced in bacillarydysenteries induced by Shigella. Thus, this paper describes anovel mechanism used by bacteria to increase their virulence.Findings: Using RT-PCR and immunohistochemistry on gut biop-sies from patients infected with Shigella, the authors showed thatthe expression of the bactericidal LL-37 and HBD-1 was severelyreduced early after the onset of the disease. Shigella also downregulated the expression of LL-37 and HBD-1 upon in vitroinfection of the colonic epithelial cell line, HT-29. Furthermore, theauthors showed that this phenomenon was not mediated by bacterial proteins but rather by Shigella DNA.

Microbial lipopeptides stimulate dendritic cell maturationvia Toll-like receptor 2. Hertz CJ, Kiertscher SM, Godowski PJ,Bouis DA, Norgard MV, Roth MD, Modlin RL: J Immunol 2001,166:2444-2450.• Significance: Although microbial lipopeptides have beenreported to induce the maturation of dendritic cells (DCs), themechanism by which this occurs was not known. This paper isthe first to show that Toll-like receptor (TLR)-2 plays a criticalrole in this phenomenon thereby providing a mechanism bywhich lipopeptides act as adjuvants.Findings: The authors found that human peripheral bloodmononuclear cell (PBMC)-derived immature DCs differentiatedinto fully mature DCs upon in vitro incubation with a lipoproteinfrom M. tuberculosis or a synthetic lipopeptide. They furthershow that the lipid portion of the lipopeptide was required forthe induction of DC maturation. Most importantly, lipopeptide-induced maturation was blocked by preincubating the immatureDCs with anti-TLR2 antibodies.

Epstein-Barr virus coopts lipid rafts to block the signalingand antigen transport functions of the BCR. Dykstra ML,Longnecker R, Pierce SK: Immunity 2001, 14: 57-67.• Significance: Epstein−Barr virus (EBV) persists in humanB cells during latent infection. As LMP2A is the only viral productthat is consistently detected in cells latently infected with EBV, thisprotein is believed to be critical for EBV persistence. AlthoughLMP2A was previously demonstrated to inhibit both BCR signal-ing and antigen transport, the mechanism by which this occurswas not known. This paper sheds some new light on this process.Findings: The authors first demonstrated that LMP2A was con-stitutively present in lipid rafts in an EBV-infected humanlymphoblastoid cell line. They further showed that LMP2A pre-vented the BCR from entering the rafts upon BCR crosslinking.However, experiments using cells expressing a mutated form ofLMP2A suggested that LMP2A-mediated inhibition of BCR rafttranslocation did not result from the ability of this viral protein toinhibit BCR signaling.

Selected by Anna VyakarnamKing’s College London, London, UK

Isolation of primary HIV-1 that target CD8+ T lymphocytesusing CD8 as a receptor. Saha K, Zhang J, Gupta A, Dave R,Yimen M, Zerhouni B: Nat Med 2001, 7:65-72.

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• Significance: Clear evidence for HIV infectability of CD8+

T cells is presented and has implications for the understandingof HIV pathogenesis and treatment.Findings: Using CD8+ T cell clones isolated from AIDSpatients that spontaneously produced HIV as a source of virus,the authors carried out in vitro infection of CD8+ T cells puri-fied from normal peripheral blood. Replication of theCD8+-cell-derived virus strains was noted to be equally efficient in CD8+ and CD4+ T cells. A combination of antibody-blocking experiments and infection of receptor− cells showedthat HIV infection of CD8+ T cells was CD4-, CCR5- andCXCR4-independent but CD8-dependent. Interestingly, not allHIV strains infected CD8+ T cells in vitro — for example the HIVstrain IIIB, extensively catalogued in the literature as capable ofreplicating in peripheral blood lymphocytes and CD4+ T cells,failed to replicate in CD8+ T cells. In contrast, the CD8+-cell-derived strains maintained tropism for CD4+ T cells.Comparing the envelope sequences of the CD8+-cell-derivedstrains with IIIB showed conservation of the CD4-bindingregion but extensive changes in the V1-V2 variable loops. Onlya single amino acid change was noted in the gp41 transmem-brane protein sequence of the CD8+-cell-derived straincompared with IIIB, suggesting that envelope mutations in theCD8+-cell-derived viruses, that can alter virus tropism, wereunlikely to be random events.

A Toll-like receptor recognises bacterial DNA. Hemmi H,Takeuchi O, Kawai T, Kaisho T, Sato S, Sanjo H, Matsumoto M,Hoshino K, Wagner H, Takeda K, Akira S: Nature 2001,408:740-745.• Significance: This paper describes a mechanism by whichbacterial DNA can induce innate immunity in mammalian cells.TLR9, belonging to a highly conserved family of pattern-recog-nition receptors, has been shown on murine immune cells torecognise bacterial DNA consisting of unmethylated pairs ofthe nucleotides cytosine and guanosine (CpG). UnmethylatedCpG sequences are 20-times more common in bacterial com-pared with mammalian DNA, so mammalian TLR9 is more likelyto be activated by bacterial than self DNA. This discoveryshould help in understanding how CpG DNA is recognised,how such recognition leads to immune Th1 cell activation andhow recognition of CpG DNA contributes to host defenseagainst bacteria; therefore it should help in understanding andimproving DNA-based vaccines.Findings: A BLAST search identified an expressed sequencetag (EST) clone that showed high similarity to previously iden-tified TLRs. A gene was identified in murine and human cellsand designated TLR9. Confocal microscopy data showedthat TLR9 tends to localise in endosomal compartmentsrather than the cell membrane. The biological function ofTLR9 was studied using TLR9−/− mice. Splenocytes werespecifically defective in terms of proliferation and cytokine(TNF-α, IL-6 and IL-12) production to bacterial CpG DNAalthough the defect was not present when cells were stimu-lated with other bacterial components. The in vivo responseto CpG DNA was studied by in a protocol that induces lethalshock of wild-type mice, with elevated serum concentrationsof TNF-α, IL-6 and IL-12. TLR9−/− mice, however, survived thischallenge. In wild-type mice, CpG DNA normally induces aTh1-biased cytokine response via IFN-γ; in contrast TLR9–/–

mice failed to produce IFN-γ. TLR9–/– macrophages showedimpaired activation of NF-κB in response to CpG. Exploitationof the potent induction of TLR9-mediated Th1 cytokine

responses by using bacterial CpG sequences as an adjuvantin DNA-based vaccines will depend on reducing the detri-mental effects of toxic shock that may also result fromactivating TLR9.

Substantial differences in specificity of HIV-specific cyto-toxic T cells in acute and chronic HIV infection. Goulder PJR,Altfield MA, Rosenberg ES, Nguyen T, Tang Y, Eldridge RL,Addo MM, Kalams SA, Sekaly RP, Walker BD, Brander C:J Exp Med 2001, 193:181-193.• Significance: Cytotoxic T lymphocytes (CTLs) have beenshown to be important in curtailing human virus infections,including infection with HIV. The generation of effective HIVvaccines is dependent on the induction of an HIV-specific CTLresponse and the identification of CTL epitopes inHIV-encoded proteins. Although several CTL epitopes in HIVhave been documented, these have been largely identified inindividuals with chronic infection. This paper shows that awell-documented HLA-A*0201 epitope in p17 Gag that isrecognised in chronic HIV infection is not recognised in acuteHIV infection. These observations are important for HIV vaccinedesign, given that the immune response in acute infection iscritical for virus clearance and influences the virus set point thatsubsequently governs disease outcome.Findings: HIV-specific CTL responses in acute infection weremeasured in IFN-γ ELISPOT assays to the immunodominantHLA-A*0201 p17 gag epitope, SLYNTVATL (SL9) and to apanel of 15−20-mer overlapping peptides that overlapped by10 amino acids covering other HIV proteins — p24 gag, Nef,RT, gp120 and gp41. Individual peptides previously definedas optimal epitopes for the HLA class I alleles expressed byeach subject were also tested — in all, 78 optimal epitopepeptides were used in studies of 11 A*0201+ subjects withearly HIV infection. None of the 11 subjects studied hadresponses to A*0201-SL9 epitope although responses tomultiple epitopes other than SL9 were detected. The lack ofresponse to A*0201-SL9 epitope was confirmed by intracel-lular IFN-γ staining after peptide stimulation or usingtetrameric complexes of peptide with MHC class I.Sequencing of patients’ virus showed that the failure torecognise the A*0201-SL9 epitope was not due to mutationsin the autologous virus covering the SL9 consensussequence. In longitudinal studies of two acutely infected indi-viduals, the authors show recognition of the A*0201-SL9epitope emerging later in disease, providing strong evidencethat the A*0201-SL9-specific response is not required for theinitial control of viremia in A*0201+ subjects.

ImmunogeneticsSelected by Jean-Laurent CasanovaLaboratory of Human Genetics of Infectious Disease, Necker-EnfantsMalades Medical School, Paris, France

A novel X-linked disorder of immune deficiency and hypo-hidrotic ectodermal dysplasia is allelic to incontinentiapigmenti and due to mutations in IKK-gamma (NEMO).Zonana J, Elder ME, Schneider LC, Orlow SJ, Moss C,Golabi M, Shapira SK, Farndon PA, Wara DW, Emmal SA,Ferguson BM: Am J Hum Genet 2000, 67:1555-1562.

ANDIncontinentia pigmenti in a surviving male is accompaniedby hypohidrotic ectodermal dysplasia and recurrent infec-tion. Mansour S, Woffendin H, Mitton S, Jeffery I, Jakins T,Kenwrick S, Murday VA: Am J Med Genet 2001, 99:172-177.

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ANDAtypical forms of incontinentia pigmenti in male individualsresult from mutations of a cytosine tract in exon 10 of NEMO(IKK-γγ). Aradhya S, Courtois G, Rajkovic A, Lewis RA, Levy M,Israel A, Nelson DL: Am J Hum Genet 2001, 68:765-771.

ANDSpecific missense mutations in NEMO result in hyper-IgMsyndrome with hypohydrotic ectodermal dysplasia. Jain A,Ma CA, Liu S, Brown M, Cohen J, Strober W: Nat Immunol2001, 2:223-228.

ANDX-linked anhidrotic ectodermal dysplasia with immunodefi-ciency is caused by impaired NF-κκB signaling. Döffinger R,Smahi A, Bessia C, Geissmann F, Feinberg J, Durandy A,Bodemer C, Kenwrick S, Dupuis-Girod S, Blanche S et al.:Nat Genet 2001, 27:277-285.•• Significance: These papers report on hypomorphic muta-tions in NEMO, responsible for a clinical syndrome known asX-linked anhidrotic ectodermal dysplasia with immuno-deficiency (EDA-ID). This is the first identified primary immuno-deficiency of the NF-κB signalling pathway.Findings: X-linked recessive EDA-ID is a rare clinical syndrome inwhich the patient has no sweat glands, sparse scalp hair, rare con-ical teeth and unusually severe infections despite mild detectableimmunological abnormalities. Mutations in NEMO were identifiedin patients with EDA-ID and a related syndrome with osteopetrosisand lymphedema (OL-EDA-ID). Mutations in the coding region areassociated with EDA-ID, and stop codon mutations are associatedwith OL-EDA-ID. NEMO encodes the regulatory subunit of the IKKcomplex, which is essential for NF-κB signalling. Germline loss-of-function mutations in NEMO were previously shown to be lethal inmale foetuses (affected by an X-linked dominant syndrome knownas incontinentia pigmenti). NEMO mutations causing OL-EDA-IDand EDA-ID were shown to be milder, as they impair but do notabolish NF-κB signalling. EDA was shown to result from impairedNF-κB signalling through Eda-receptors. Abnormal immunity wasshown to result from impaired cell responses to lipopolysaccharide,IL-1β, IL-18, TNF-α and CD154. In conclusion, impaired but notabolished NF-κB signaling in humans results in two related syndromes which associate specific developmental and immuno-logical defects.

ImmunotherapySelected by Yang LiuOhio State University, Columbus, OH, USA

Targeting of lymphotoxin-alpha to the tumors elicits an effi-cient immune response associated with induction ofperipheral lymphoid-like tissue. Schrama D, Straten P,Fisher WH, McLellan A, Brocker E-B, Reisfeld RA, Becker JC:Immunity 2001, 14:111-121.•• Significance: The first demonstration that induction ofneolymphoid genesis in the tumor can be exploited for tumorimmunotherapy.Findings: A fusion protein, consisting of a recombinant anti-body and lymphotoxin-α , elicited lymphoid-like tissue inmelanoma. This was associated with both qualitative and quan-titative enhancement of antitumor CD8+ T cell response withinthe tumors and increased resistance to both metastasis andlocal growth of melanoma.

Immunization with a HER-2/neu helper peptide vaccinegenerates HER-2/neu CD8 T-cell immunity. Knutson KL,Schiffman K, Disis ML: J Clin Invest 2001, 107:477-484.

• Significance: An impressive study in a significant number ofbreast cancer patients that demonstrates the value ofHER-2/neu peptide containing both MHC class-II- andclass-I-binding epitopes.Findings: When 19 breast cancer patients with HER-2/neuoverexpression received four peptides containing both CD4+

and CD8+ T cell epitopes, the majority of them developedstrong proliferative and CTL responses as a result of immuniza-tion. The patients developed long-term immunological memoryand a CTL clone prepared from an immunized patient wascapable of lysing cancer cells with overexpression of theHER-2/neu gene.

Persistence of immunogenic pulmonary metastasis in thepresence of protective anti-melanoma immunity. Donawho CK,Pride MW, Kripe ML: Cancer Res 2001, 61:215-221.• Significance: This interesting study highlights an important differ-ence between systemic immunity and local immunity in the lung andthus has important implications for therapy of metastatic cancers.Findings: The excision of local melanoma was followed bydevelopment of systemic immunity to subcutaneous challengewith tumor cells. However, despite the systemic immunity, themice died of lung metastasis. Analysis of multiple cell lines iso-lated from the lung metastasis revealed that the lack ofimmunity was not due to loss of tumor antigens, as measuredby either in vivo or in vitro assays.

Allergy and hypersensitivitySelected by Cezmi AkdisSwiss Institute of Allergy and Asthma Research, Davos, Switzerland

Effects of an interleukin-5 blocking monoclonal antibody oneosinophils, airway hyper-responsiveness, and the lateasthmatic response. Leckie MJ, ten Brinke A, Khan J,Diamant Z, O’Connor BJ, Walls CM, Mathur AK, Cowley HC,Chung KF, Djukanovic R et al.: Lancet 2000, 356:2144-2148.• Significance: Eosinophils are predominant cells in sputum,bronchoalveolar lavage and mucosal biopsy samples of asthmapatients. IL-5 is responsible for terminal differentiation of humaneosinophils and is involved in eosinophilic inflammation in asthma,representing one of the most common drug targets in asthma.This trial aimed to assess the effects of a monoclonal antibody(mAb) to IL-5 on blood and sputum eosinophils, airway hyper-responsiveness and the late asthmatic reaction in allergic asthma.Findings: A single intravenous infusion of anti-IL-5 mAb causedpronounced long-term suppression of circulating eosinophils,and to a large extent lowered the degree of sputum eosinophiliaafter allergen challenge. Very interestingly, despite these cleareffects on eosinophils, the treatment did not protect against theallergen-induced late asthmatic response and did not haveeffects on airway hyper-responsiveness. These findings sug-gest that eosinophils might not be a prerequisite for the lateasthmatic response and airway hyper-responsiveness andquestion the relevance of eosinophils to the pathogenesis andtreatment of asthma.

Effects of recombinant human interleukin-12 oneosinophils, airway hyper-responsiveness, and the lateasthmatic response. Bryan SA, O’Connor BJ, Matti S,Leckie MJ, Kanabar V, Khan J, Warrington SJ, Renzetti L,Rames A, Bock JA et al.: Lancet 2000 356:2149-2153.• Significance: The inflammatory response in asthma isthought to be caused by a defect in immune regulation involv-ing T helper lymphocytes, with an increase in Th2 lymphocytes.

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IL-12 is a key cytokine in regulating the balance between Th1and Th2 cells. IL-12 inhibits Th2 cytokine synthesis, leading toinhibition of eosinophilia and IgE. In addition, IL-12 inhibited air-way hyper-responsiveness and airway eosinophilia in severalanimal models with allergen sensitization and thus appeared asa candidate drug for the treatment of human asthma. Findings: Systemic IL-12 treatment caused an influenza-like syn-drome in most of the patients and 4 out of 19 were withdrawnfrom the study. A decrease in blood and sputum eosinophils anda trend towards improvement in airway hyper-responsivenesswere observed. However, no effect on airway hyper-responsive-ness to inhaled allergen was observed. This is analogous to thefinding that anti-IL-5 mAb caused profound suppression of bloodand sputum eosinophils without healing effects on airway hyper-responsiveness and late asthmatic response (see Leckie et al.,above). Together, these studies question the role of eosinophilsin asthma and have important implications for development ofnew anti-inflammatory treatments.

Mast cells control neutrophil recruitment during T cell-mediated delayed-type hypersensitivity reactions throughtumor necrosis factor and macrophage inflammatory pro-tein. Biederman T, Kneilling M, Mailhammer R, Maier K,Sander CA, Kollias G, Kunkel SL, Hültner L, Röcken M:J Exp Med 2001, 192:1441-1451.• Significance: This paper demonstrates a novel, unexpectedrole for mast cells, showing that they are not only involved inallergic reactions, and the initiation and amplification of delayedtype hypersensitivity (DTH) reactions, but also determine thepattern of cells infiltrating into sites of inflammation through thechemokines they produce.Findings: Mast cells determine the T cell dependent neutrophilrecruitment through two mediators, TNF and the murine ana-logue of human IL-8 — macrophage inflammatory protein 2(MIP-2). MIP-2 protein was highly accumulated in DTH areas ofwild-type mice but absent in mast cell deficient (Kitw/Kitw-v)mice. T cell dependent neutrophil recruitment was reduced byanti-MIP-2 antibodies and in mast cell deficient mice. Mast cellsfrom wild-type mice efficiently restored neutrophil recruitment inKitw/Kitw-v mice. Mast cells from TNF–/– mice did not restoreneutrophil recruitment, showing the effect of mast cell TNF inneutrophil recruitment to inflammatory areas. Together theseresults demonstrate that mast cell derived TNF and MIP-2determine whether neutrophils infiltrate T cell mediated inflammatory reactions.

AutoimmunitySelected by Allison GreenDepartment of Medical Genetics, Addenbrooke’s Hospital,Cambridge, UK

Linkage disequilibrium of a type 1 diabetes susceptibilitylocus with a regulatory IL12B allele. Morahan G, Huang D,Ymer SI, Cancilla MR, Stephen K, Dabadghoa P, Werther G,Tait BD, Harrison LC, Colman PG: Nat Genet 2001, 27:218-221.•• Significance: The destruction of the insulin-producingβ-cells in type 1 diabetes (T1D) relies on both genetic and envi-ronmental factors. The strongest genetic association to date isthe MHC although many other genes are required for diseasesusceptibility. Here the authors identify a new diabetes sus-ceptibility locus, termed IDDM18, which is located in proximityto the IL-12-p40 gene, IL12B. The data presented provide astrong link between IDDM18 and T1D, and suggest that IL12Bis a candidate diabetes susceptibility gene in humans.

Findings: Genetic and functional studies in nonobese (NOD)mice, a murine model for T1D, have demonstrated a role forIL-12 in promoting diabetes. To determine whether IL-12 mayplay a role in human T1D, the authors genetically typed 249 sibpairs for markers on chromosome 5q33−34, where IL12B islocated. They found a bias in transmission of certain IL12Balleles in HLA-matched sibpairs that developed diabetes, asopposed to HLA-mismatched sibpairs that did not. Sequencingstudies identified a single-base change in the IL12B 3′ UTR(untranslated region), which showed strong linkage disequilib-rium with the IL12B locus. The 3′ UTR allele 1 was preferentiallytransmitted to T1D subjects whereas the 3′ UTR allele 2 wasnot, suggesting that allele 1 was disease promoting and allele 2was disease resistant. Further, studies in Epstein−Barr virus(EBV)-transformed cell lines demonstrated that homozygosityfor allele 1 resulted in significantly higher protein levels of IL-12,in comparison with EBV-transformed cell lines that werehomozygous for IL12B 3′ UTR allele 2. Considering that T1D inNOD mice is associated with increased Th1 cytokines, thentransmission of IL12B 3′ UTR allele 1 may result in higher levelsof the Th1-promoting cytokine, IL-12, and help perpetuate diabetes development in man.

An unexpected version of horror autotoxicus: anaphylacticshock to a self-peptide. Pedotti, R, Mitchell D, Wedemeyer J,Karpuj M, Chabas D, Hattab EM, Tsai M, Galli SJ, Steinman L:Nat Immunol 2001, 2:216-222.•• Significance: Certain autoimmune diseases of man, likeT1D and multiple sclerosis (MS), are characterised by elevated Th1 responses and decreased Th2 responses. Manytherapeutic strategies currently under investigation aredesigned to enhance Th2 responses following injection ofpeptides (either self or altered-self) and, as a consequence,prevent destruction of host tissue. This paper, although notdirectly addressing the issue of autoimmunity, is worth rec-ommending as the data suggest that we should treadcautiously in developing therapeutic strategies that increaseTh2 responses in autoimmune disease, since this may resultin allergic anaphylaxis, which may cause damage to host tissue and potentially worsen the disease.Findings: To date, allergic reactions that follow treatment ofT1D patients with self autoantigens have been linked to impu-rities in the antigen preparations rather than self-antigensthemselves. Here the latter possibility was tested in EAE, amurine model for human MS. SJL/J mice develop EAE follow-ing injection of the self-antigenic peptide PLP(p139−151).Symptoms of immediate hypersensitivity occurred in 71% ofmice rechallenged with the peptide 3−4 weeks after primaryinjections and many of the mice died; if rechallenge wasdelayed until 14 weeks, only 12% developed hypersensitivityand none died. Serum anti-PLP IgG1 levels (a measure of Th2responses) increased 3−4 weeks post priming; this corre-lated with EAE remission. Rechallenge when antibody levelswere highest resulted in allergic reactions in 91% of mice.Similar findings were also seen for a different antigen/mousesystem although symptoms were less severe. Interestingly,allergic reactions could not be elicited to self antigens thatwere expressed in the thymus. Finally, injections of mast celldegranulation inhibitors to mice immunised and rechallengedwith PLPp(139−151) ameliorated disease. Thus, therapeuticinterventions with self antigens designed to increase Th2 lev-els may in fact induce greater tissue damage due to ananaphylactic response.

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Uncoupling the proinflammatory from the immunosuppres-sive properties of tumour necrosis factor (TNF) at the p55TNF receptor level: implications for pathogenesis and ther-apy of autoimmune demyelination. Kassiotis G, Kollias G:J Exp Med 2001, 193:427-434.• Significance: MS in humans is characterised by an acutephase followed by remission. Many studies analysing theimmune response in MS have focused on the acute phase ofthe disease, with few data available about the immune mecha-nisms responsible for remission. TNF has been linked to thedevelopment of autoimmune disease (including arthritis, T1Dand MS) and therapeutic strategies designed to block TNF sig-nals are under investigation as a means of preventing MS.However, preliminary results have suggested that total block-ade of TNF signals is detrimental in MS, the reason for which isunknown. Here, the authors present data that show why suchtherapeutic strategies may fail by demonstrating not only thatTNF is important in the acute phase but also that it is a criticalcomponent for inducing disease remission.Findings: Injection of MBP (in the absence of pertussis toxin)into B6 mice does not induce clinical or histological evidence

of EAE but can induce T cell responses to MBP. The authorsdemonstrated that TNF deficient (B6,129.TNF–/–) miceshowed enhanced anti-MBP T cell responses up to 49 dayspost immunization and accumulated MBP-specific T cells in thespleen. Further, such mice developed clinical evidence of EAE,which progressed into a chronic nonremitting disease. Controlmice exhibited no evidence of responses to MBP and remainedhealthy. Whereas both MBP-specific responses and diseaseprogression were controlled in B6,129.p55−/− mice (lackingp55 TNF receptor), mice deficient in both TNF receptors(B6,129.p75–/–p55–/–) had a similar phenotype toB6,129.TNF–/– mice; this suggests that TNF receptor p75 maybe critical for disease regression (although it is important topoint out that the authors did not show evidence to support thislatter hypothesis). Similar results were obtained using a secondautoantigen. Failure of MOG-reactive T cell regression to occurwas linked to increased and sustained memory CD4+ T cellresponses to MOG in the susceptible mice, suggesting thatTNF influences the expansion or survival of activated/memoryMOG-specific T cells through a pathway independent of p55TNF receptor.

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