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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 2000, 12:355–364

Contents (chosen by)

355 Antigen recognition (Elliott)356 Innate immunity (Bonneville)356 Lymphocyte development (Kruisbeek)357 Immunological techniques (Liu)357 Lymphocyte activation and effector functions (Casolaro)359 Immunity to infection (Glaichenhaus)359 HIV (Rowland-Jones)360 Genetic effects on immunity (Casanova)360 Cancer (Walker)361 Transplantation (Wood and Bushell)362 Atopic allergy and other hypersensitivities (Gorham)363 Autoimmunity (Green)

• of special interest•• of outstanding interest

Antigen recognitionSelected by Tim ElliottJohn Radcliffe Hospital, Oxford, UK

The roles of CD28 and CD40 ligand in T cell activation andtolerance. Howland KC, Ausubel LJ, London CA, Abbas AK:J Immunol 2000, 164:4465-4470.• Significance: This study attempts to evaluate the induction ofT cell responses to a defined antigen in vitro and in vivo in theabsence of either the costimulatory molecule CD28 (a ligandfor B7) or CD40L (a ligand for CD40). In doing so it shows howantagonists to each of these costimulatory molecules couldskew an antigen-specific CD4+ T cell response towards eithera Th1 or Th2 pathway. These costimulatory molecules could beused as ‘intelligent’ adjuvants in therapeutic regimes where thepriming of a particular T cell subtype is beneficial.Findings: Mice that were transgenic for a TCR recognising anovalbumin-derived peptide restricted by class II MHC (TCRTgmice) were crossed onto either a CD28-knockout or CD40L-knockout background. This study revealed that neithercostimulatory molecule was required for T cell maturation in thethymus as both crosses expressed normal numbers of trans-genic T cells in the periphery. Naive CD4+ T cells isolated fromthe TCRTg × CD28-knockout showed around 100-times lessproliferation and IL-2 secretion compared with cells isolatedfrom wild-type mice when stimulated with autologous antigen-presenting cells pulsed with the appropriate peptide.Proliferation of cells isolated from the TCRTg × CD40L-knock-out was also impaired but not to the same extent. Neither IL-2nor IL-4 could be detected in cultures of stimulated T cells fromthe TCRTg × CD28-knockout mice but IFN-γ secretion was nor-mal. Converseley, IL-2 and IL-4 but no IFN-γ was detected insimilar cultures established from the TCRTg × CD40L-knockoutmice. In the latter case this defect was restored by adding IL-12to the cultures, suggesting that the function of CD40L is to

induce IL-12 production in antigen-presenting cells. No prolif-eration of CD4+ T cells, or secretion of IL-2 or IFN-γ, wasdetected after in vivo immunisation in either of the strains ofTCRTg × knockout mice; the authors ascribe this to the factthat, in vivo, antigen is limiting.

Induction of human cytotoxic T lymphocytes by artificialantigen-presenting cells. Latouche JB, Sadelain M: NatBiotechnol 2000, 18:405-409.• Significance: Passive immunotherapy using specific anti-bodies or T cells requires the induction and expansion ofspecific B or T cells. In the latter case a therapeutic regimenmight require the infusion of between 1 × 109 and 1 × 1010

cells in humans. Here, artificial antigen-presenting cells com-prising mouse cells expressing costimulatory molecules wereused to prime and expand specific human cytotoxic T lym-phocytes (CTLs). This approach overcomes the technicaldifficulty in using autologous dendritic cells for this purposeand should minimise the risk of generating potentially harmfulautoreactive responses.Findings: The human class I MHC molecule HLA-A2.1 wasintroduced into murine NIH/3T3 fibroblasts along with humanβ2 microglobulin, B7.1 (CD80), ICAM-1 (CD54) and LFA-3(CD58) using a replication-incompetent retroviral vector. Inaddition, the fibroblasts were stably transfected with minigenesexpressing one of three immunogenic peptides expressedbehind a leader sequence: influenza A matrix protein peptideGILGFVFTL (single-letter code is used for amino acids),MART-1 peptide AAGIGILTV and gp-100 peptideIMDQVPFSV. This strategy not only allowed for continuousexpression of the antigenic epitope but also overcame incom-patibilities in function between mouse antigen-processingmolecules (TAP and tapasin) and human class I MHC mole-cules. Naive T cells isolated from human peripheral blood wereco-cultured with these target cells for 8–10 days, after whichgood CTL responses were detected. These responses were upto four-times better than those obtained after stimulation withpeptide-pulsed autologous dendritic cells. Some priming wasalso seen with stimulators lacking CD54 and CD58. Re-stimu-lation of the cultures led to an improvement in the specific CTLresponse and an expansion in the number of cells per culture.

Increased efficiency of folding and peptide loading ofmutant class I molecules. Beisbarth T, Sun J, Kavathas PB,Ortmann B: Eur J Immunol 2000, 30:1203-1213.• Significance: The intracellular loading of class I MHC mole-cules with antigenic peptide epitopes in the endoplasmicreticulum (ER) requires their interaction with cofactors such asTAP, tapasin, calreticulin and ERp57. It is not clear how impor-tant these interactions are for the formation of a functionalantigen-presenting complex. On the one hand, mutant class Imolecules have been made that do not interact with thesecofactors and do not assemble correctly or present peptidesbut on the other hand some naturally occurring class I MHCalleles that function well as antigen-presenting moleculesappear to interact poorly with these cofactors in co-immuno-precipitation experiments. This study resolves this paradox byshowing that an apparently poor interaction could reflect a low

ImmunologyPaper alert

level of steady-state binding resulting from rapid assembly andpeptide loading.Findings: Seven single-site mutants of the human class I MHCmolecule HLA-A2.1 (Q115A, D122A, D129A, S132A, T134A,D137A and A245V) and one double mutant (D102A plusR111A) were screened for their ability to bind to TAP, tapasinand calreticulin. Two of these (Q115A and D122A) bound verypoorly. Interestingly the mutant T134A bound well: in studiesfrom other groups the mutation T134K (that is to say substitu-tion of the threonine at position 134 for lysine rather thanalanine) abrogated binding to all ER cofactors including TAPand prevented peptide-loading and antigen presentation. Theauthors showed that Q115A and D122A assemble with β2microglobulin (β2-m) and peptides more rapidly than wild-typemolecules and so are transported to the cell surface morerapidly. They assemble with a normal repertoire of peptides. It isunlikely that these mutations directly affected the binding siteon the class I molecule for TAP–tapasin–calreticulin because —when peptide supply was restricted by treating cells with theprotease inhibitor, LLnL — a stable, prolonged interaction wasvisible between the mutants and the TAP complex. ResiduesQ155 and D122 point towards the β2-m binding site in thewild-type molecule and so mutations at these positions couldconceivably assist assembly of the heavy chain with β-2m,thereby promoting more rapid formation of a stable complex ofclass I MHC and peptide.

Innate immunitySelected by Marc BonnevilleInstitut de Biologie, Nantes, France

HSP70 stimulates cytokine production through a CD14-dependent pathway, demonstrating its dual role as achaperone and cytokine. Asea A, Kraeft SK, Kurt-Jones EA,Stevenson MA, Chen LB, Finberg RW, Koo GC,Calderwood SK: Nat Med 2000, 6:435-442.• Significance: This study provides the first convincing evi-dence that the 70 kDa heat shock protein (HSP70), a wellknown intracellular molecular chaperone, can also act as anextracellular protein to trigger production of proinflammatorycytokines by monocytes. This observation could explain the pre-viously reported adjuvant effect of HSP70 in various immuneresponses and more particularly in tumor immunity.Findings: It is shown that recombinant HSP70 binds with highaffinity to monocytes, elicits intracellular calcium flux, activatesnuclear factor κB (NF-κB) and upregulates the production ofthe proinflammatory cytokines IL-1β, IL-6 and TNF-α by mono-cytes. These effects are mediated by at least two signaltransduction pathways: one depends on CD14 receptors andresults in increased IL-1β, IL-6 and TNF-α expression; the otheris independent of CD14 receptors and results in increasedTNF-α expression only.

Lymphocyte developmentSelected by Ada KruisbeekThe Netherlands Cancer Institute, Amsterdam, The Netherlands

The duration of antigen receptor signalling determinesCD4+ versus CD8+ T cell lineage. Yasutomo K, Doyle C,Miele L, Germain RN: Nature 2000, 404:506-510.• Significance: How does a developing thymocyte decide tobecome a CD4+ or a CD8+ T cell? The precursors that gener-ate these cells express both the CD4 and the CD8co-receptors, and one of the most fascinating puzzles in devel-opmental immunology is how most CD4+ cells end up with

MHC class II restricted TCRs whereas CD8+ cells generallyexpress MHC class I restricted TCRs. This study investigateshow this match is achieved.Findings: In a two-stage culture system, naive CD4+CD8+ thy-mocytes are first subjected (while in suspension culture) todendritic cells (DCs) that do or do not express wild-type ormutant MHC molecules (initiating cultures) and then subjectedto thymic stroma and DCs in a reaggregate culture system (dif-ferentiating cultures), again under varying MHC-expressionconditions. In the initiating culture, no lineage choice is made —the CD4+CD8+ thymocytes merely mature to the CD69+

stage. It was found that the CD4+/CD8+ lineage decision iscontrolled by the duration of the initial TCR-dependent interac-tion in differentiating cultures and that this duration isinfluenced by interactions between co-receptor and MHC. Inaddition it is shown that Notch-1 activity is not required forCD4+ lineage commitment or progression but is involved inallowing CD8+ T cell maturation to occur, after lineage com-mitment has been made.

Notch1 deficiency dissociates the intrathymic developmentof dendritic cells and B cells. Radtke F, Ferrero I, Wilson A,Lees R, Aguet M, MacDonald HR: J Exp Med 2000,191:1085-1093.• Significance: Do thymic dendritic cells (DCs) represent alymphoid lineage derived from a common T-cell/DC precursoror is thymic DC-lineage specification established in an inde-pendent thymic precursor population? This study providesevidence that thymic DC development can be dissociated fromT cell development.Findings: Mice in which the Notch1 gene had been condition-ally inactivated were used as bone marrow (BM) donors forlethally irradiated recipients. As expected, such mice exhibit avery early block in T cell development (see also F Radtke et al.,Immunity 1999, 10:547-548.). Development of other lymphoidor myeloid lineages is not affected by Notch1 deficiency: BMchimeras reconstituted with induced Notch1-deficient BM dis-play normal macrophage, granulocyte, NK and B celldevelopment. In addition, they have entirely normal thymic DCdevelopment. This latter result is inconsistent with the generallyheld belief that thymic DCs are derived from a commonT-cell/DC precursor downstream of the T-cell/B-cell lineagechoice. Rather, the data are compatible with the hypothesis thatthymic DCs and T cells are derived from distinct precursors.

Role of CD8ββ domains in CD8 coreceptor function: impor-tance for MHC I binding, signaling, and positive selection ofCD8+ T cells in the thymus. Bosselut R, Kubo S, Guinter T,Kopacz JL, Altman JD, Feigenbaum L, Singer A: Immunity2000, 12:409-418. • Significance: Does the CD8β chain have a role duringselection of the T cell repertoire? The answer to this questionappears to be yes, since both positive and negative selectionare perturbed in mice lacking CD8β. This is puzzling, sincethe CD8αα homodimers that are still expressed on thymo-cytes from such CD8β-deficient mice should be able toperform the functions which the CD8 coreceptor is thought toperform in selection.Findings: The study design is very straightforward: CD8β-defi-cient mice are reconstituted through expression of eithercomplete or partial CD8β transgenes. By comparing T celldevelopment in mice reconstituted with complete CD8β, withonly the extracellular or with only the intracellular domain of

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CD8β, an assessment can be made of the contribution of boththe MHC-binding and the Lck-binding positions of CD8β.Surprisingly, the extracellular and the intracellular domains ofCD8β can independently reconstitute positive selectionalthough the full-length CD8β chain is more efficient. This invivo effect of CD8β transgenes is correlated with greater bind-ing of MHC class I to CD8αβ heterodimers than to CD8ααhomodimers. LAT and Lck also bind more effectively to CD8αin the presence of the CD8β intracellular domain. Together,these observations may explain the greater efficacy of CD8coreceptor function in presence of CD8β.

Entry of B cell receptor into signaling domains is inhibitedin tolerant B cells. Weintraub BC, Jun JE, Bishop AC,Shokat KM, Thomas ML, Goodnow CC: J Exp Med191:1443-1448.• Significance: Tolerance for self antigens in the B lineage canmanifest itself (among other mechanisms) by an inability of theBCR to trigger a proliferative response whereas other BCR-triggered functions remain intact. Indeed, antigen receptors onboth T and B cells can couple to multiple signaling pathways;this represents the basis for the large diversity of functions theycan trigger. How then is the signal specification that dictatesB cell tolerance induced?Findings: In T and B cells, antigen binding results in accumu-lation of a portion of the antigen receptors into membrane rafts.These dynamic membrane structures are enriched for src-fam-ily protein tyrosine kinases (PTKs) and certain scaffold proteins;association of these components with the receptors in rafts isthought to be necessary for initiation of signaling. NormalB cells are shown here to form rafts within seconds and theserafts are enriched for the kinase, Lyn, and depleted of the phos-phatase, CD45. Amazingly, tolerant B cells do not efficientlymobilize their BCRs into rafts. Non-responsiveness may there-fore already be dictated at this very early step of BCR signaling.

Immunological techniquesSelected by Yang LiuOhio State University, Columbus, OH, USA

Differentiating between memory and effector CD8 T cellsby altered expression of cell surface O-glycans.Harrington LE, Galvan M, Baum L, Altman JD, Ahmed R: J ExpMed 2000, 191:1241-1246.• Significance: A monoclonal antibody, 1B11, that recognizesO-glycans on mucin-type glycoproteins can be used to distin-guish memory T cells from effector T cells. This antibody maybecome a much needed tool in understanding T cell differenti-ation after antigen stimulation.Findings: The 1B11 epitope is dramatically upregulated onvirus-specific T cells during the effector, but not the memory,phase of both primary and secondary cytotoxic T lymphocyteresponse in vivo. This upregulation correlates with the effectorfunction of the CD8+ T cells.

Enzymatic amplification staining for flow cytometric analy-sis of cell surface molecules. Kaplan D, Smith D: Cytometry2000, 40:81-85.• Significance: The authors characterized and improved apreviously described enzymatic amplification of staining forflow cytometry. This method allows 10–100-fold increase insensitivity in analysis of cell surface molecules and shouldbe valuable for analysis of molecules that are expressed atlow levels.

Findings: The authors applied this procedure to analysis of alarge panel of cell surface molecules, such as MHC class I andII, CD3, CD4, CD5, CD6, CD7, CD34, CD45 and phosphatidylserine. The significant improvement in sensitivity permits cleardelineation of human peripheral-blood leukocytes expressing ornot expressing Fas ligand and permits efficient sorting of thetwo populations.

Overcoming adeno-associated virus vector size limitationthrough viral DNA heterodimerization. Sun L, Li J, Xiao X: NatMed 2000, 6:599-602.• Significance: A novel strategy that allowed adeno-associatedvirus (AAV) vector to deliver genes of up to 10 kilobases, thusdoubling the size limit of genes that can potentially be deliveredby an AAV vector.Findings: A large gene can be split into two fragments andpacked into two separate viral particles. Heterodimerization ofthe two fragments allowed rejoining of the gene when trans-duced into the same cells.

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

Th2 responses induced by epicutaneous or inhalationalprotein exposure are differentially dependent on IL-4.Herrick CA, MacLeod H, Glusac E, Tigelaar RE, Bottomly K:J Clin Invest 2000, 105:765-775.•• Significance: Recent literature provides overtly conflictingdata on the role of IL-4 in the generation of Th2 responses.Although IL-4-independent Th2 responses can be elicited inparasite-infected mice, studies involving immunization with pro-tein antigen indicate a strong reliance on IL-4 for theseresponses. In this study, Herrick et al. test the hypothesis that —besides and irrespective of the nature of the antigen — it is theinitial route of exposure that determines the pathway of Th2 cellgeneration and activation.Findings: Prolonged exposure of C57BL/6J mice to soluble pro-tein antigen (ovalbumin [OVA]) via either the epicutaneous orinhalational routes induced systemic Th2 activation, as evidencedby selectively increased levels of OVA-specific IgG1 and IgE andthe induction of airway eosinophilia following subsequent airwaychallenge with the same antigen. Th2 responses elicited byinhalational sensitization were impaired in IL-4-deficient mice. Incontrast, these responses were preserved in IL-4-deficient micesensitized via the epicutaneous route. Epicutaneous Th2 sensiti-zation was instead impaired following depletion of IL-13 and inmice deficient for the IL-4/IL-13-dependent factor STAT6. Thesefindings identify the skin as a highly effective site for activation ofIL-13-dependent Th2 responses to protein antigens.

Single cell analysis reveals that IL-4 receptor/Stat6 signal-ing is not required for the in vivo or in vitro development ofCD4+ lymphocytes with a Th2 cytokine profile. Jankovic D,Kullberg MC, Noben-Trauth N, Caspar P, Paul WE, Sher A:J Immunol 2000, 164:3047-3055.• Significance: The once-established notion that IL-4 pro-vides a critical signal for Th2 cell differentiation has beenquestioned in several recent studies. In particular, Th2responses induced by Schistosoma mansoni were at leastpartially preserved in mice made unable to either express orrespond to IL-4. In this study the occurrence of Th2 popula-tions has been analyzed at the single-cell level inS. mansoni-infected, IL-4-unresponsive mice.

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Findings: Using either antibodies interfering with in vitro class-II-restricted antigen presentation or purified T cellsubpopulations, residual IL-4 expression from IL-4-receptor α(IL-4Rα)-deficient mice infected with S. mansoni was localizedto CD4+ T cells. However, the frequency of T cells producingIL-4 was much lower in the mutant than in the correspondingwild-type strain; this was paralleled by an increased frequencyof IFN-γ-producing cells. A similar change was seen in micedeficient for the IL-4-dependent factor Stat6. The relative per-centage of IL-4-producing cells from IL-4Rα-deficient orStat6-deficient, but not wild-type, mice was temporarilyreduced following in vitro exposure to the Th1-promotingcytokine IL-12. Although these data suggest that IL-4-elicitedsignals can influence the frequency and phenotypic stability ofTh2 clones from helminth-infected mice, integrity of these sig-nals was not necessary for in vitro development of Th2 clonesfrom uninfected animals.

T1/ST2-deficient mice demonstrate the importance ofT1/ST2 in developing primary T helper cell type 2responses. Townsend MJ, Fallon PG, Matthews DJ, Jolin HE,McKenzie ANJ: J Exp Med 2000, 191:1069-1075.• Significance: The IL-1-receptor-related molecule, T1/ST2,has been reported to be selectively expressed on the surfaceof Th2 cells. Although the biological function of T1/ST2 hasnot been identified, its in vivo blockade can partially inhibit Th2cell differentiation and the development of Th2-dependentallergic responses. However, these responses are preservedin a recently developed T1/ST2-deficient murine model. Thisstudy represents a timely effort to reconcile these apparentlycontradictory findings.Findings: The T1/ST2 gene was disrupted by homologousrecombination in murine embryonic stem cells. Basal immuno-logic parameters — including T cell and B cell surfacephenotype, immunoglobulin isotype distribution and ex vivo Thcell development and cytokine expression — did not appear tobe affected in the resulting T1/ST2-deficient strains. However,the pulmonary primary granulomatous response following intra-venous injection of schistosome eggs — characterized bymassive eosinophil infiltration — was decreased by greater than90% in T1/ST2-deficient mice. In contrast, formation of sec-ondary granulomas and the development of specificimmunoglobulin isotype responses in presensitized animalswere not affected by the absence of this receptor, in spite ofdramatically reduced antigen- and mitogen-induced ex vivo Th2cytokine expression. Thus, although T1/ST2 appears to play afundamental role in the generation of Th2 responses, disruptionof this pathway does not prevent the development of down-stream effector responses — presumably due to the involvementof alternative mechanisms.

A novel transcription factor, T-bet, directs Th1 lineage com-mitment. Szabo SJ, Kim ST, Costa GL, Zhang X, Fathman CG,Glimcher LH: Cell 2000, 100:655-669.•• Significance: Early findings by Glimcher and colleaguessuggested that T helper cell polarization depends on devel-opmentally regulated expression of lineage-restrictedtranscriptional activators. Although several Th2-restrictedfactors — including c-Maf, GATA-3, and STAT6 — have beencharacterized since then, their Th1-restricted counterpart(s)have not been identified to date. This article reports on thecloning and characterization of a novel Th1-restricted IFN-γ activator.

Findings: Using a yeast one-hybrid assay of a previously identi-fied Th1-specific region of the IL-2 promoter, the authorsidentified a novel clone sharing homology with the T box familyof transcription factors. Expression of this protein, named T-bet(i.e. T box expressed in T cells), is restricted to Th1 cells (i.e.among T cells) and appears to be augmented in response toTCR ligation. T-bet expression is induced relatively early underTh1-polarizing conditions in both T and non-T (i.e. B and NK)immune cells and is highly correlated with expression of the Th1cytokine IFN-γ. Indeed, this factor is a potent, direct transactiva-tor of the IFN-γ gene — perhaps via binding to an intronic regionpreviously found to be responsible for Th1-restricted expressionof this cytokine. IFN-γ expression is dramatically increased as aresult of T-bet overexpression and can be induced in transientlytransfected EL4 cells and in retrovirally transduced primaryCD4+ T cells. While inducing IFN-γ, ectopically expressed T-betcan repress IL-4 and IL-5 production in developing Th2 clonesas well as established Th2 clones. The inhibitory effect of T-beton IL-4 expression is not mediated by upregulated IFN-γ anddoes not involve direct binding of this factor to the IL-4 proximalpromoter. In conclusion, T-bet — the first lineage-restricted Th1activator identified to date — appears to play a major role in theregulation of T cell effector responses.

Differential production of prostaglandin D2 by humanhelper T cell subsets. Tanaka K, Ogawa K, Sugamura K,Nakamura M, Takano S, Nagata K: J Immunol 2000,164:2277-2280.• Significance: The pivotal role of prostaglandin (PG)D2 in thedevelopment of asthma has been confirmed in a recently devel-oped PGD2-receptor-deficient murine model. Although mastcells are deemed to be the primary source of PGD2 in allergicresponses, several reports indicate that effector T cells can syn-thesize variable levels of this mediator. In this study theexpression of PGD2 and PG-synthetic enzymes in distincthuman T helper clones has been correlated with their cytokine-expressing phenotype and, inherently, their ability to elicitallergic responses.Findings: The authors demonstrate that an enzyme, hematopoi-etic PGD synthase (hPGDS), is selectively and constitutivelyexpressed, at both the protein and mRNA level, in IL-4-produc-ing Th2 clones. Upon stimulation mediated by anti-CD3 plusanti-CD28, Th2 lines produced substantial amounts of PGD2.This was paralleled by selective induction of cyclo-oxygenase(COX)-2 expression in these lines. Within human peripheral-blood leukocytes, hPGDS expression appeared to be limited toa small subset (<1%) of CD4+ T cells, to most FcεRI+ cells(basophils) and to an unidentified CD3– lineage. hPGDS-expressing T cells appeared to be CD25+CD45RA–CD45RO+

(i.e. recently activated effector/memory cells). These cells werestrongly positive for CRTH2, a Th2-related surface molecule,and appeared to preferentially express IL-4. These findingspoint to Th2 cells as an important source of PGD2 and suggesta more direct participation of these cells in the effector arm ofallergic responses than initially thought.

Control of TH2 polarization by the chemokine monocytechemoattractant protein-1. Gu L, Tseng S, Horner RM,Tam C, Loda M, Rollins BJ: Nature 2000, 404:407-411.• Significance: The chemokine monocyte chemoattractant pro-tein (MCP)-1 can stimulate IL-4 expression in T helper cells.MCP-1 overexpression in mutant mice has been associatedwith defective Th1-driven cellular immunity. This study makes

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use of a MCP-1-deficient murine model to formally demonstratethe contribution of this chemokine to the development of Th2responses.Findings: T cells from MCP-1-deficient mutant mice and thecorresponding wild-type strain immunized with trinitrophenol-derivatized ovalbumin (TNP-OVA) secreted the same amountsof IFN-γ and IL-2 in response to in vitro challenge with the sameantigen. In contrast, expression of IL-4, IL-5 and IL-10 wasremarkably lower in cells from MCP-1-deficient mice.Consistent with this apparent Th1 bias, sera from the same ani-mals contained selectively reduced total and TNP-specific IgG1titers and increased IgG2a and IgG2b. In addition, MCP-1-defi-cient mice could not mount a Th2 response to Leishmaniainfection and, for this reason, developed a less progressive dis-ease than their wild-type counterparts. Taken together, thesefindings indicate that MCP-1, perhaps via binding to Th2-restricted CCR2 or CCR4, is a critical activator of Th2responses that are elicited by protein antigen or parasites.

CD28, Ox-40, LFA-1, and CD4 modulation of Th1/Th2 dif-ferentiation is directly dependent on the dose of antigen.Rogers PR, Croft M: J Immunol 2000,164:2955-2963.• Significance: The relative strength of TCR-delivered signalsappears to be a major determinant in T helper cell commitmenttoward distinct cytokine-expressing phenotypes. However, thisresponse is compounded by the interaction with a diverse arrayof costimulatory ligands expressed in antigen-presenting cells(APCs). This study was aimed at understanding how individualcostimulatory signals integrate with each other and with TCRsignals in a previously defined in vitro model of antigen-depen-dent T helper cell differentiation.Findings: Naive CD4+ cells from mice transgenic for a TCR spe-cific for a peptide of moth cytochrome c (MCC) were stimulatedwith varying doses of the MCC analogue T102S presented bysyngeneic splenic APCs. Whereas low doses of antigen weresufficient to induce preferential IL-2 expression, intermediatedoses induced the appearance of IL-4-, IL-5- and IL-13-produc-ing Th2-like clones and very high doses were necessary formaximal expression of the Th1 cytokine IFN-γ. Using stimulatingor blocking antibodies toward a panel of T cell costimulatoryreceptors, the authors confirm previous findings that engagementof some of these molecules can preferentially promote expres-sion of either a Th1 or Th2 cytokine profile (e.g. LFA-1 or CD4,respectively). However, the developmental potential of theseinteractions appeared to vary as a complex function of both thepriming dose of peptide antigen and the relative strength andcomposition of the costimulatory signal provided.

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

CD8+ T cells can block herpes simplex virus type 1 (HSV-1)reactivation from latency in sensory neurons. Liu T, KhannaKM, Chen XP, Fink DJ, Hendricks RL: J Exp Med 2000,191:1459-1466.•• Significance: Primary HSV-1 infection in humans usuallyoccurs early in life often without overt clinical manifestations.Recurrent disease results from re-activation of latent virus insensory neurons and axonal transmission to peripheral sites.Using a mouse ocular model of HSV-1 infection, the authorsshow that the CD8+ T cells — which infiltrate the trigeminalganglions after the acute infection — prevent re-activation oflatent viruses by inhibiting HSV-1 replication without killing

the infected neurons. Identifying the viral antigens recognizedby these CD8+ T cells may lead to the development of aneffective vaccine.Findings: Cells from the trigeminal ganglions of HSV-1-infected mice were incubated with or without anti-CD8αantibodies. In the absence of antibodies, HSV-1 was main-tained in a latent state. In contrast, expression of HSV-1 lateproteins and production of virions were observed in cultures inwhich anti-CD8α antibodies were added.

CD1c-mediated T cell recognition of isoprenoid glycolipidsin Mycobacterium tuberculosis infection. Moody DB,Ulrichs T, Mühlecker W, Young DC, Gurcha SS, Grant E,Rosat J-P, Brenner MB, Costello CE, Besra GS, Porcelli SA:Nature 2000, 404:884-888.• Significance: CD1 MHC-class-I-like glycoproteins havebeen shown to present bacterial lipid antigens to T cells.However, both the nature of these antigens and the functionsof CD1-restricted T cells remain poorly understood. In thisstudy, the authors have identified a new class of broadly dis-tributed lipid antigens that are major components of bacterialcell walls and that are presented by CD1c molecules. Resultssuggest that T cells reacting to these antigens may play a rolein bacterial infections.Findings: Cell walls from M. avium and M. tuberculosis were frac-tionated using silica-gel chromatography techniques and thefractions were tested for their ability to stimulate a CD1c-restricted mycobacteria-specific T-cell line. Furthercharacterization of the positive fractions led to the identification oftwo natural hexosyl-1-phosphoisoprenoids and two structurallyrelated mannosyl-β1-phosphodolichols. Most importantly, theauthors show that T lymphocytes reacting to mannosyl-β1-phos-phodolichols are present in the blood of human subjects who hadrecently been infected with M. tuberculosis.

The neutrophil-activating protein (HP-NAP) of Helicobacterpylori is a protective antigen and a major virulence factor.Satina B, Giudice GD, Della Bianca V, Dusi S, Laudanna C,Tonello F, Kelleher D, Rappuoli R, Montecucco C, Rossi F:J Exp Med 2000, 191:1467-1476.• Significance: This study demonstrates for the first time thatthe neutrophil activating protein of Helicobacter pylori (HP-NAP) is indeed a virulence factor. This work provides insightsinto the mechanisms by which H. pylori induces the inflamma-tion of the human gastric mucosa. It may also have importantimplications for vaccine design.Findings: The authors found that purified HP-NAP attracts neu-trophils and promotes their adhesion by upregulating theexpression of β2-integrin-family receptors. HP-NAP alsoinduces neutrophils to produce reactive oxygen intermediateswhose pathogenic effect is further amplified by the inflamma-tory cytokines TNF-α and IFN-γ induced by H. pylori. Mostimportantly, the authors show that vaccination with HP-NAPprotects mice against H. pylori challenge.

HIVSelected by Sarah Rowland-JonesJohn Radcliffe Hospital, Oxford, UK

Rapid progression to AIDS in HIV+ individuals with a struc-tural variant of the chemokine receptor CX3CR1. Faure S,Meyer L, Costagliola D, Vaneensberghe C, Genin E, Autran B,Delfraissy JF, McDermott DH, Murphy PM, Debre P et al.:Science 2000, 287:2274-2277.

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• Significance: This report describes novel polymorphisms inthe Fracktalkine receptor that have a major impact on HIV disease progressionFindings: A number of polymorphisms in the chemokinereceptors used by HIV for entry into CD4+ cells, and in the lig-ands which bind them, have a demonstrable effect on HIVdisease progression. It has been hard to explain how some ofthese mutations would exert their effects; an example is theinfluential point mutation in CCR2 (CCR2-64I), which has lit-tle impact on receptor function and occurs in a receptor onlyrarely used by the virus. The story is further complicated by thisreport, which shows that a combination of two mutations(V249I and T280M) in CX3CR1 — the receptor for thechemokine Fracktalkine — is associated with rapid HIV diseaseprogression. This receptor has only recently been identified asan HIV co-receptor and is expressed at high levels on acti-vated lymphocytes and in the brain. Homozygotes for theM280 mutation showed significantly more rapid disease pro-gression to a low CD4+ T cell count and clinical AIDS.Although the CX3CR1 gene lies on chromosome 3 in theregion of the CCR2 and CCR5 genes, there was no apparentlinkage of the CX3CR1 polymorphisms with previouslydescribed disease-modifying mutations in these co-receptorgenes. Functional analysis of the receptor from M280 homozy-gotes showed reduced Fracktalkine binding. It remains to beestablished why these new mutations in a little-used HIV co-receptor should lead to accelerated HIV disease progression.

Initiation of antiretroviral therapy during primary HIV-1infection induces rapid stabilization of the T-cell receptorbeta chain repertoire and reduces the level of T-cell oligo-clonality. Soudeyns H, Campi G, Rizzardi GP, Lenge C,Demarest JF, Tambussi G, Lazzarin A, Kaufmann D, Casorati G,Corey L, Pantaleo G: Blood 2000, 95:1743-1751.

ANDEarly highly active antiretroviral therapy for acute HIV-1infection preserves immune function of CD8+ and CD4+T lymphocytes. Oxenius A, Price DA, Easterbrook PJ,O’Callaghan CA, Kelleher AD, Whelan JA, Sontag G,Sewell AK, Phillips RE: Proc Natl Acad Sci USA 2000,97:3382-3387.• Significance: These two papers examine the impact of highlyactive antiretroviral therapy (HAART) on different aspects of thecellular immune response to acute HIV infection.Findings: An important question in HIV management iswhether potent antiretroviral therapy initiated early after infec-tion can alleviate some of the immune impairment associatedwith HIV infection. Alternatively, others have suggested thatearly suppression of viral load may actually prevent the devel-opment of an effective anti-HIV cellular response and couldtherefore be detrimental. In the first of these papers, the TCRrepertoire was studied in a cohort of 23 subjects with primaryHIV infection with or without antiretroviral therapy. Ten out ofeleven treated patients showed progressive stabilisation oftheir TCR repertoire. Stabilisation was also seen in seven out ofeleven untreated seroconverters but the changes were smallerin magnitude. In detailed serial studies of four treated patientswho had mounted an oligoclonal response to the virus (previ-ously associated with poor prognosis), there was a gradualreversal in T cell oligoclonality over time on therapy. In the sec-ond study, HIV-specific CD4+ and CD8+ T cell responses werestudied in a small group of eight patients (treated or untreated).Far from suppressing HIV-specific responses, it appeared that

therapy initiated very early in infection was able to maintain theCD8+ T cell response to HIV antigens. Even more significantly,HIV-specific CD4+ T cell responses were preserved in patientstreated early; this would be expected to improve substantiallytheir long-term immunity to the virus.

Genetic effects on immunitySelected by Jean-Laurent CasanovaLaboratory of Human Genetics of Infectious Diseases, Necker-EnfantsMalades Medical School, Paris, France

Mutations in the tyrosine phosphatase CD45 gene in achild with severe combined immunodeficiency disease.Kung C, Pingel JT, Heikinheimo M, Klemola T, Varkila K, Yoo LI,Vuopala K, Poyhonen M, Uhari M, Rogers M: Nat Med 2000,6:343-345.• Significance: This is the first identification of severe com-bined immunodeficiency (SCID) associated with CD45mutations and the first identification of a human tyrosine-phos-phatase-specific inherited defect.Findings: A child with no detectable αβ T cells but with normalor elevated numbers of γδ T cells, B cells and NK cells in theblood (T–B+NK+ SCID) was investigated. Serum immunoglob-ulin isotypes levels decreased to very low or undetectablelevels with time. A maternally inherited large deletion was foundin one CD45 gene. A splice mutation was identified in thepatient’s second CD45 gene, probably resuting from a de novomutation in the paternal germline. In a B cell line derived fromthe child, there was no detectable CD45 mRNA by northernblotting but aberrant splicing was shown by RT-PCR. No CD45molecules were detected at the cell surface by flow cytometry.

CancerSelected by Paul R WalkerUniversity Hospital Geneva, Geneva, Switzerland

T cell activity after dendritic cell vaccination is dependenton both the type of antigen and the mode of delivery.Serody JS, Collins EJ, Tisch RM, Kuhns JJ, Frelinger JA:J Immunol 2000, 164:4961-4967.

ANDImmune deviation and Fas-mediated deletion limit antitu-mor activity after multiple dendritic cell vaccinations inmice. Ribas A, Butterfield LH, Hu B, Dissette VB, Meng WS,Koh A, Andrews KJ, Lee M, Amar SJ, Glaspy JA et al.: CancerRes 2000, 60:2218-2224.

ANDMature dendritic cells boost functionally superior CD8+

T-cells in humans without foreign helper epitopes.Dhodapkar MV, Krasovsky J, Steinman RM, Bhardwaj N: J ClinInvest 2000, 105:R9-R14.• Significance: Dendritic cells (DCs) may be the tumourimmunotherapist’s favourite adjuvant, but do we really knowhow to use them? In the mouse, Serody et al. and Ribas et al.induced robust immune responses by DC vaccination but theresponses diminished after frequent multiple vaccinations.These results should alert us to potential problems in protocolsfor clinical cancer therapy. The study of Dhodapkar et al. inhumans is important, since it thoroughly monitors immuneresponses after DC vaccination (in normal individuals) and pro-vides valuable data on the kinetics of T cell immunity. Findings: Serody et al. studied cytotoxic T lymphocyte (CTL)responses to a peptide (in some cases modified to giveenhanced MHC binding) derived from the human proto-onco-gene HER-2/neu. The site of DC injection affected the

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distribution of CTLs and the kinetics (but not the magnitude) ofthe response. The immunisation regime that diminished CTLresponses consisted of multiple injections of peptide-pulsedDCs at weekly intervals. Ribas et al. studied specific T cellimmune responses and tumour protection induced by DCstransduced with the MART-1 gene. An adverse effect of multipleDC immunisations was noted but this was strain specific. Thiseffect also correlated with a switch from Th1 to Th2 cytokineresponse and appeared to be influenced by Fas since the reduc-tion in immune responses were not observed in lpr mice.Dhodapkar et al. studied responses to keyhole limpet haemo-cyanin, tetanus toxoid and influenza matrix peptide in normalindividuals immunised twice with antigen-pulsed DCs, with a7–9 month interval. Under these conditions the booster injectionelicited a more rapid and higher magnitude of response, withT cells exhibiting enhanced sensitivity to peptide.

Gene therapy of experimental brain tumors using neuralprogenitor cells. Benedetti S, Pirola B, Pollo B, Magrassi L,Bruzzone MG, Rigamonti D, Galli R, Selleri S, Di Meco F,De Fraja C et al.: Nat Med 2000, 6:447-450. • Significance: The resistance of glioblastomas to currenttreatments (chemotherapy, radiotherapy and surgery) meansthat novel therapeutic approaches are urgently required. Localdelivery of immunostimulatory (or other) factors is attractive butgenerally inefficient because of the disseminated nature ofglioblastoma growth. In the novel approach described here byBenedetti et al., local delivery of IL-4 is achieved by CNSengraftment of transduced primary or immortalised neural prog-enitor cells that migrate into the brain parenchyma; this resultsin significant antitumour effects.Findings: Induction of antitumour immunity with retroviral trans-fer of IL-4 has previously been demonstrated by this group in ratbrain tumour models but here improved efficacy was achievedby use of IL-4-transduced neural progenitor cells. This may benot only due to some additional antitumour effect of the neuralstem cell (without IL-4) but also because the engrafted stemcells migrated through the parenchyma and could be found inthe vicinity of the tumour. Furthermore, the syngeneic GL261mouse glioma could also be treated by this procedure. Whilstthe results with IL-4 are encouraging, the particular interest ofthe approach is that it may also be compatible with delivery ofother therapeutic molecules for tackling the ultimate challengeof human glioblastoma.

Monitoring CD8 T cell responses to NY-ESO-1: correlationof humoral and cellular immune responses. Jäger E,Nagata Y, Gnjatic S, Wada H, Stockert E, Karbach J,Dunbar PR, Lee SY, Jungbluth A, Jäger D et al.: Proc Natl AcadSci USA 2000, 97:4760-4765.• Significance: Reliable monitoring of specific immuneresponses to human tumour antigens continues to be techni-cally challenging, particularly for CD8+ T cell responses.Serological screening of cDNA expression libraries (SEREX)has allowed the identification of several tumour antigens suchas the NY-ESO-1. Patients mounting an immune response tothis antigen tend to show both specific antibodies and CD8+

T cell responses, confirming the utility and relevance of sero-logical tests in overall immune response screening forNY-ESO-1 and perhaps for other SEREX-defined antigens.Findings: A group of 36 advanced cancer patients wereassessed for immune reactivity to NY-ESO-1 by serology,ELISPOT assays, cytotoxicity tests and NY-ESO-1–HLA-A2

tetramer binding. Out of the 27 patients positive for NY-ESO-1mRNA, 11 were antibody positive and 10 of these patientsshowed specific CD8+ T cell immunity after a period of in vitropresensitisation with peptide. T cell responses were notdetected in patients without NY-ESO-1 antibody.

Multiple genetic alterations cause frequent and heteroge-neous human leukocyte antigen class I loss in cervicalcancer. Koopman LA, Corver WE, van der Slik AR, Giphart MJ,Fleuren GJ: J Exp Med 2000, 191:961-975.• Significance: The phenomenon of loss of HLA expression inhuman cancer is well described, particularly for tumour celllines, but how frequently this occurs in primary tumours is lessclear. In this study of cervical cancer, a combination of flowcytometry and molecular analyses showed that the majority offreshly isolated cervical tumour cell preparations had defectiveHLA expression. This may explain one factor leading to tumourescape from spontaneous immunity and has profound implica-tions for the design of T cell based immunotherapies.Findings: Of the 30 cervical cancers analysed, 90% had alter-ations in expression of at least one HLA class I allele.Multiparameter flow cytometry was the preferred detectionmethod for HLA expression due to its superior sensitivity andthe possibility of using a wider array of antibodies than wereappropriate for immunohistochemistry. Molecular analysesrevealed that multiple genetic defects were responsible forHLA loss; most were irreversible genetic changes at chromo-some 6p.

TransplantationSelected by Kathryn Wood and Andrew BushellJohn Radcliffe Hospital, Oxford, UK

Stable mixed chimerism and tolerance using a nonmye-loablative preparative regimen in a large-animal model.Huang CA, Fuchimoto Y, Scheier-Dolberg R, Murphy MC,Neville DM, Sachs DH: J Clin Invest 2000, 105:173-181.• Significance: Bone-marrow transplantation has been usedfor many years to treat life-threatening lymphoproliferative dis-eases but it also has great potential for the treatment of othermalignancies and of haemoglobinopathies and for the inductionof tolerance in organ transplantation. Many studies, mostly inrodent models, have demonstrated that stable chimerismallows indefinite allograft survival without chronic immunosup-pression. However, most of these protocols involve severemyeloablative treatment of the recipient which significantly lim-its their clinical applicability. Recently, nonmyeloablativeprotocols have been developed in the mouse (see T Wekerleet al., J Exp Med 1998, 187:2037-2044.). The paper of Huanget al. presents the first description of a nonmyeloablative mixedchimerism protocol in a clinically relevant large-animal model.Findings: Mini-pig recipients were given two 150 cGy doses ofwhole body irradiation on consecutive days plus 700 cGy ofthymic irradiation. Mature T cells were depleted using an anti-CD3-antibody–diphtheria-toxin conjugate (pCD3-CRM9).Administration of this antibody–immunotoxin resulted in greaterthan 99% depletion of peripheral T cells two days after treat-ment. Conditioned recipients were then given donor stem cellsharvested either from donor bone marrow or donor peripheralblood. Stem cell donors were matched with the recipient for theMHC but mismatched for minor antigens. Multilineage (lym-phoid and myeloid) chimerism was readily detected in therecipients irrespective of whether they received bone marrow orperipheral-blood lymphocyte (PBL) stem cells. Although

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absolute numbers varied between different recipients, donorcells could be detected as early as 5 days post-infusion andwere relatively stable up to at least 400 days. Function and tol-erance of the developing PBLs were demonstrated by therejection of third party and the acceptance of donor skin graftsrespectively. Although these grafts were mismatched only forminor transplantation antigens the results suggest that such aprotocol could provide long-term survival of HLA matched (butminor antigen mismatched) grafts without chronic immunosup-pression and offer the possibility that, with subtle modifications,such protocols could be successful in HLA incompatible grafts.

Reversal of insulin-dependent diabetes using islets gener-ated in vitro from pancreatic stem cells. Ramiya VK,Maraist M, Arfors KE, Schatz DA, Peck AB, Cornelius JG: NatMed 2000, 6:278-282.• Significance: Insulin dependent diabetes mellitus (IDDM) isan autoimmune disease with an incidence of up to 0.5% insome populations. For almost all patients, insulin therapy is theonly available treatment and, although very successful in theshort term, many individuals develop secondary complicationssuch as nephropathy, vasculopathy, retinopathy and cataracts.Most of these complications are thought to arise because of thefailure of insulin therapy to provide a precise and regulated con-trol of glucose levels. Transplantation may offer an alternativeand more effective long-term treatment for IDDM and manybelieve that transplantation of islets rather than whole pancreasis the preferred option. However, the results of clinical islettransplantation have so far been somewhat disappointing. Onemajor problem is the retrieval of sufficient numbers of purifiedislets from a single cadaveric donor. Findings: The authors of the current paper have previouslyreported that it possible to establish cultures of islet-produc-ing stem cells (IPSC) from digested pancreatic tissueharvested from pre-diabetic NOD mice (JG Cornelius et al.,Horm Metab Res 1997, 29:271-277.). These IPSC can begrown for extended periods in culture and give rise to mono-layers from which islet-progenitor cells (IPC) develop. Moststriking is the fact that islets can be harvested repeatedly fromthese cultures and can provide a 10,000-fold increase over thenumber of islets available from a single pancreas. These isletsexpress transcripts characteristic of ‘normal’ islets such asinsulin, glucagon and glucose-transporter-2-receptor but,more importantly, secrete insulin in response to a glucose chal-lenge. When transplanted into diabetic NOD mice either underthe kidney capsule or in a subcutaneous pocket, these islets(combined with a 2–5 day course of insulin) were able to main-tain normoglycemia for up to 100 days. The data demonstratethat it is possible to derive significant numbers of IPSC fromthe adult mouse pancreas which could provide a potentialsource of islets for xenotransplantation. More importantly, ifthese observations can be extended to the adult human pan-creas, the generation of almost unlimited numbers ofwell-matched functional islets for allotransplantation couldbecome a real possibility.

Atopic allergy and other hypersensitivitiesSelected by James GorhamDartmouth Medical School, Lebanon, NH, USA

Prostaglandin D2 as a mediator of allergic asthma.Matsuoka T, Hirata M, Tanaka H, Takahashi Y, Murata T,Kabashima K, Sugimoto Y, Kobayashi T, Ushikubi F, Aze Y et al.:Science 2000, 287:2013-2017.

• Significance: Mast cells release numerous bioactive sub-stances upon allergen-induced cross-linking of surface IgE.Prostaglandin D2 (PGD2) is the predominant cyclo-oxygenasemetabolite of arachidonic acid in mast cells. This study showsthat the PGD2 is required for airway hyper-reactivity, inflamma-tion and Th2 responses in a mouse model of antigen-elicitedairway sensitization.Findings: The PGD2 receptor (DP) was deleted in mice byhomologous recombination. DP+/– mice were back-crossedfive generations to the C57Bl/6 inbred strain of mouse and theninter-crossed to generate DP–/– mice. DP–/– mice were resis-tant to experimentally induced airway hyper-responsiveness inan ovalbumin challenge model. Pulmonary inflammation andTh2 cytokine levels were greatly reduced in challenged DP–/–

mice, compared with control mice. The requirement for PGD2appeared to be local, as antigen-specific systemic IgEresponses were not diminished in DP–/– mice.

Identification of a coordinate regulator of interleukins 4, 13,and 5 by cross-species sequence comparisons. Loots GG,Locksley RM, Blankespoor CM, Wang ZE, Miller W, Rubin EM,Frazer KA: Science 2000, 288:136-140.•• Significance: The genes that encode the Th2 cytokines IL-4,IL-5 and IL-13 are clustered within a 200-kilobasepair segmenton the long arm of human chromosome 5. Whether there isfunctional significance to this clustering, or if it is merely agenetic relic of some ancient gene duplication event, has beena matter of some speculation. In this study, the authors use afascinating genomics approach to identify a conserved geneticelement within this cluster that co-regulates the expression ofthese three cytokines.Findings: Using database searches, the authors identified 90noncoding long sequences (>100 basepairs) that are con-served between the human 5q31 chromosomal region and itsmurine counterpart (>70% identity). A 401-basepair sequence(CNS-1) that is conserved across several vertebrate speciesand located in the intergenic region between IL-4 and IL-13was selected for further study. A 450-kilobasepair YAC encod-ing this portion of human 5q31 was modified to insert loxP sitesflanking CNS-1 and then used to create 5q31 transgenic mice.Mating of 5q31-YAC transgenic mice with Cre recombinasetransgenic mice allowed for the generation of lines of trans-genic mice containing the 5q31-YAC transgene with a deletionin CNS-1. The authors found that the production of the humanTh2 cytokines IL-4, IL-5 and IL-13 was significantly lower in Th2cells from CNS-1-deleted 5q31-YAC transgenic mice than inTh2 cells from CNS-1-intact 5q31-YAC transgenic mice. Th2cell production of murine IL-4 and IL-13, as well as of humanRAD50 (a 5q31 gene that is not specific to Th2 cells), was notdifferent between the two types of transgenic mice, indicatingthat CNS-1 acts in a cis fashion and is able to discriminatebetween Th2 genes and non-Th2 genes. Interestingly, intracel-lular cytokine analysis by flow cytometry showed that CNS-1affected the number of Th2 cells producing human Th2cytokines but not the amounts of cytokine per expressing cell.This shows that the CNS-1 element primarily functions to reg-ulate commitment of the T cell to Th2 cytokine expression butdoes not influence the level of gene expression once that com-mitment has been made.

A novel transcription factor, T-bet, directs Th1 lineage com-mitment. Szabo SJ, Kim ST, Costa GL, Zhang X, Fathman CG,Glimcher LH: Cell 2000, 100:655-669.

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•• Significance: Several transcription factors — including c-Maf, GATA-3 and NF-ATc — promote Th2 development inantigen-stimulated naïve CD4+ T cells. By contrast, very little isknown about the transcriptional machinery that promotes Th1development. This study identifies T-bet, a member of the T-boxfamily of transcription factors, as a potent inducer of the Th1developmental pathway.Findings: T-bet was isolated using a yeast one-hybrid selectionapproach that incorporated the Th1-specific region of the IL-2gene and was identified as a new member of the T-box family oftranscription factors, defined by a 200-amino-acid conservedDNA-binding domain. T-bet expression was detected in Th1 butnot in Th2 clones and in naïve CD4+ T cells activated underTh1-inducing, but not Th2-inducing, conditions. Expression ofT-bet in murine T cell lines trans-activated IFN-γ promoter con-structs; retroviral expression of T-bet in TCR-stimulated primaryCD4+ T cells greatly augmented IFN-γ production. In addition,T-bet expression in differentiated Th2 cells induced IFN-γexpression and suppressed IL-4 and IL-5 expression.

AutoimmunitySelected by Allison GreenYale University School of Medicine, and The Howard Hughes MedicalInstitute, New Haven, CT, USA

B7/CD28 costimulation is essential for homeostasis of theCD4+CD25+ immunoregulatory T cells that control autoim-mune diabetes. Salomon B, Lenschow LR, Ashourian N,Singh B, Sharpe A, Bluestone JA: Immunity 2000,12:431-440.• Significance: CD28/B7 costimulation has been implicated inthe progression or prevention of autoimmunity. In insulin-depen-dent diabetes mellitus (IDDM), deficiency of CD28 or B7exacerbates disease. Here the authors establish that, in part,disease exacerbation in these two models is linked to theabsence of regulatory CD4+CD25+ T cells.Findings: By backcrossing mice deficient in either B7 costim-ulatory molecules (B7–/– mice) or CD28 (CD28–/– mice) to thenonobese diabetic (NOD) mouse, diabetes exacerbation wasapparent as early as the N4 generation backcross, with respectto wild-type (wt) littermates. Rapid progression to diabetes wascharacterized by earlier recruitment of inflammatory cells to theislets, when mice were 7–9 weeks of age. Interestingly, Th1and Th2 cytokine responses to diabetogenic antigens werereduced compared with wt mice, suggesting that a selectivedecrease in protective Th2 cytokines alone in B7–/– mice doesnot account for rapid disease progression. Detailed analysis ofthe CD4+ T cell populations in the spleen and lymph nodes ofB7–/– compared with B7+/+ mice suggested that B7–/– micehad fewer CD4+CD25+ T cells that wt mice. This decreasednumber of CD4+CD25+ T cells was also apparent in CD28–/–

mice. Such cells have previously been documented to containa population of regulatory cells that delay tissue destruction inseveral autoimmune and inflammation-based diseases. Further,the authors demonstrated that transfer of CD4+CD25+ T cellsfrom wt mice to CD28–/– mice delayed diabetes progression.These data suggested that the deficit of CD4+CD25+ T cells inB7/CD28–/– NOD mice contributes to disease exacerbation.

Tumour necrosis factor-related apoptosis-inducing ligand(TRAIL) is an inhibitor of autoimmune inflammation and cellcycle progression. Song K, Chen Y, Göke R, Wilmen A,Seidel C, Göke A, Hilliard B, Chen Y: J Exp Med 2000191:1095-1103.

•• Significance: This article describes a new role for TRAIL as aprototype inhibitor protein that inhibits the development of arthritis.Findings: The authors created a secretory death receptor 5(sDR5) molecule that can bind specifically to TRAIL and pre-vent apoptosis of tumour cells in vivo. In a model ofexperimentally induced arthritis they established that injectionof sDR5 resulted in both accelerated and more severe synovi-tis, hyperplasia of synovial membrane and cartilage and/or bonedestruction in most synovial foot joints compared with miceinjected with a control protein. In addition, sDR5-treated micehad increased anti-collagen B and T cell responses.Bromodeoxyuridine labeling determined that blocking TRAILsignals with sDR5 resulted in a higher proportion of cyclingcells compared with control mice whereas treatment withTRAIL resulted in arrest of cell cycle progression. Thus the dataindicate that TRAIL is involved in preventing arthritis develop-ment by inhibition of cell cycle progression of lymphocytes,including autoreactive B and T cells.

A soluble form of CTLA-4 in patients with autoimmune thy-roid disease. Oaks MK, Hallet KM: J Immunol 2000,164:5015-5018.• Significance: Cytotoxic T lymphocyte associated gene 4(CTLA-4) is a member of the immunoglobulin gene superfamilyand can bind to B7 molecules. Signaling through CTLA-4 onT cells results in anergy and is thought to be important in main-taining tolerance to host tissue. Genomics have demonstratedthat the CTLA-4 gene is polymorphic and it has been sug-gested that certain polymorphic forms of CTLA-4 are linked tothe development of autoimmune diseases like Graves diseaseand diabetes. This article suggests that a native soluble form ofCTLA-4 is derived from one of these alternative transcripts forCTLA-4 and this contributes to the development of autoimmunethyroid disease (ATD).Findings: Analysis of serum samples from ATD and normalpatients revealed that 11 out of 20 ATD patients had detectableserum CTLA-4 levels compared with 1 out of 30 normal indi-viduals. Of these 11 patients, 8 had Graves disease and theremainder suffered from Hashimoto’s thyroiditis. This solubleCTLA-4 was shown to be functional and could be neutralizedby B7-1–Ig fusion proteins. Further, by western blotting analy-sis, the serum CTLA-4 in ATD patients was shown to bepredominantly derived from polymorphic transcripts lacking atransmembrane domain and not generated from proteolyticdigestion or shedding of the CTLA-4 integral membrane pro-tein. These data may offer a link between the geneticsusceptibility to ATD and differences in the expression of vari-ous forms of the CTLA-4 molecule.

Retargeting T cell-mediated inflammation: a new perspec-tive on antibody action. Lou Y-H, Park K-K, Agersborg S,Alard P, Tung KSK: J Immunol 2000, 164: 5251-5257.•• Significance: This study shows that, in murine autoimmuneovarian disease, autoantibody can influence both T-cell-medi-ated inflammation and organ dysfunction. Findings: Ovarian zona pellucida (ZP) is an autoantigen towhich both B and T cells respond in autoimmune ovarian dis-ease (AOD). Transfer of ZP-specific CD4+ T cells into normalnon-autoimmune recipients resulted in inflammation in theatretic follicles located in the ovarian interstitium and not thegrowing mature follicles. Thus, there was no loss of ovarianatrophy or loss of fertility. In contrast, in the presence ofautoantibodies to ZP, transfer of ZP-specific CD4+ T cells

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redirected the inflammatory response both to the ovarian inter-stitium (interstitial oophoritis) and to the mature ovarianfollicles (follicular oophoritis). This resulted in disruption of theovarian histology and, as a consequence, a loss of ovarian fol-licles and ovarian atrophy. Such inflammation required both

autoantibodies and ZP-specific CD4+ T cells. Thus, the datasuggest that autoantibodies may have a role to play in autoim-munity by dictating the distribution of autoimmuneinflammation and, as a result, determine the clinical outcome ofan autoimmune disease.

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