673

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.

• of special interest•• of outstanding interest

Current Opinion in Immunology 2002, 14:673–681

Selected by Tim ElliottUniversity of Southampton, Southampton, UK

e-mail: tje@soton.ac.uk

•• T-cell engagement of dendritic cells rapidly rearrangesMHC class II transport. Boes M, Cerny J, Massol R,Op den Brouw M, Kirchhausen T, Chen J, Ploegh HL: Nature2002, 418:983-988.•• Dendritic cell maturation triggers retrograde MHC class IItransport from lysosomes to the plasma membrane. Chow A,Toomre D, Garrett W, Mellman I: Nature 2002, 418:988-994.Significance: The way in which immunostimulatory MHC:pep-tide complexes are delivered to the surface of dendritic cells(DCs), where they prime naïve T cells, is still unclear. A fullunderstanding of this process is central to our understanding ofhow immune responses are initiated. Using state of the art real-time microscopy techniques, these papers provide uniqueinsight into this process.Findings: Both studies follow the trafficking of green fluorescentprotein (GFP)-tagged MHC class II molecules in mouse DCsupon their maturation. Boes et al. constructed transgenic miceexpressing GFP–MHC class II and was able to visualiseLangerhans cells in situ in epidermal sheets where they foundthem to be dense and evenly distributed. Chow et al. followed thedistribution of GFP–MHC class II in murine bone marrow-derivedDCs transduced with the fluorescent molecule. Both groupsfound that, within 30 minutes of activation with LPS, MHC class II molecules redistributed from lysosome-like MHC class II-containing compartments (MIICs) along 5–10µM long tubules,which terminated at the plasma membrane. Chow et al. showedthat these tubules actually fuse with the plasma membrane using

evanescent wave microscopy. Significantly, Boes et al. show thatupon cognate T cell contact with activated DCs there is a rapidand pronounced tubulation of MIICs in which long (50µM)tubules terminate at the immunological synapse.

• Labeling antigen-specific CD4+ T cells with class II MHColigomers. Cameron TO, Norris PJ, Patel A, Moulon C,Rosenberg ES, Mellins ED, Wedderburn LR, Stern LJ:J Immunol Methods 2002, 268:51-69.Significance: Polyvalent MHC molecules are now key reagentsfor the detection of specific T cells ex vivo, even when they areat a very low frequency. The technology for producing tetramericMHC class II–peptide complexes has lagged behind the pro-duction of MHC class I–peptide complexes for various technicalreasons. This is the first systematic review of techniques for theproduction and use of MHC class II–peptide tetramers.Findings: Using H-DR1 as a model system, this review definesoptimum strategies for the production and use of MHC class II–peptide tetramers. It evaluates the relative merits of producing MHC class II in bacteria versus insect cells, evaluates the potential advantage of covalently linked peptideligands, and shows that different T cell clones have differentoptimal temperatures for staining amongst other useful pieces of practical information.

• Localization of the lectin, ERp57 binding, and polypeptidebinding sites of Calnexin and Calreticulin. Leach MR,Cohen-Doyle MF, Thomas DY, Williams DB: J Biol Chem 2002,277:29686-29697.Significance: Calnexin and its orthologue calreticulin areimportant cofactors in the assembly of MHC class I molecules.Together with other cofactors , such as ERp57, tapasin andTAP, they ensure that the majority of MHC class 1 moleculesleaving the endoplasmic reticulum (ER) are loaded withhigh-affinity, immunodominant peptide ligands. Calnexin has aglobular domain containing both its amino and carboxyl termini,from which extends a proline-rich arm domain. This manuscriptsheds light on the way in which calnexin and calreticulin interact with their glycoprotein substrates of which MHC class Iis but one.Findings: Using a large number of deletion constructs of calnexin and calreticulin the authors first map the oligo-saccharide binding site to the globular domain. A zinc-independent ERp57 binding site was localised to the armdomain of both molecules, at a site distal to the globulardomain. A zinc-dependant ERp57 binding site (which hasbeen described previously) was localised to the amino portion of the globular domain but was deemed to be non-specific by the authors. The polypeptide binding site wasassessed by the ability of deletion mutants to suppress temperature-induced aggregation of two model proteins (citrate synthase and malate dehydrogenase). This bindingsite was localised in the globular lectin domain, but bindingwas enhanced by presence of the arm domain.

•• Endoplasmic reticulum-mediated phagocystosis is amechanism of entry into macrophages. Gagnon E, Duclos S,Rondeau C, Chevet E, Cameron PH, Steele-Mortimer O,

ImmunologyPaper alert

Contents (chosen by)

673 Antigen processing and recognition (Elliott)674 Innate immunity (Bonneville)675 Lymphocyte development (Zúñiga-Pflücker)675 Tumour immunology (Walker)676 Lymphocyte activation and effector functions (Essayan)677 Immunity to infection (Glaichenhaus and Vyakarnam)678 Immunogenetics (Casanova)679 Immunotherapy (Liu)679 Transplantation (Auchincloss, Waneck and LeGuern)680 Allergy and hypersensitivity (Akdis)681 Autoimmunity (Green)

Antigen processing and recognition

Paiement J, Bergeron JJM, Desjardins M: Cell 2002,110:119-131.Significance: This study shows that MHC class II and, moreimportantly, MHC class I molecules, together with cofactorsessential for loading, could be delivered directly to phagosomesin phagocytic cells (such as dendritic cells [DCs]). The preciseintracellular route of antigen and MHC molecules (which mustultimately combine in the same compartment) in DCs may becritical for dictating the specificity of an immune response.Findings: During the phagocytosis of latex beads bymacrophages, the authors found calnexin, calreticulin and Sec61penriched in phagosomes by western blotting and confocalmicroscopy of purified phagosomes. Glycoproteins (some ofwhich were substrates for calnexin) could be found in phagosomeswithin five minutes of their synthesis. Phagosome formation wasfound to be mediated by the endoplasmic reticulum, which wasrecruited directly to phagocytic cups at the cell surface in order toform phagosomes. This process required phosphatidylinositol3-kinase and the proton pump ATPase. This pathway is widelyused for the phagocytosis of pathogens (such as Leishmania andSalmonella) in macrophages but not in neutrophils.

Selected by Marc BonnevilleInstitut de Biologie, Nantes, France

e-mail: bonnevil@nantes.inserm.fr

•• Release of chromatin protein HMGB1 by necrotic cellstriggers inflammation. Scaffidi P, Misteli T, Blanchi ME: Nature2002, 418:191-195.Significance: Unlike apoptotic cells, cells undergoing necrosis,for example, following a trauma or infection, elicit innatedefence mechanisms allowing their prompt elimination. Thisstudy identifies for the first time a cue specifically produced bynecrotic cells, which plays a critical role in the induction ofinflammatory responses. Findings: High mobility group 1 (HMGB1) protein is a chromatin-binding factor that is secreted by activated macrophages and ispassively released by necrotic cells. This study shows that Hmgb1-deficient necrotic cells, unlike their wild-type counterparts, have areduced ability to trigger inflammation. In particular in vivo recruit-ment of inflammatory cells is drastically decreased in Hmgb1–/–

mice following induction of massive hepatocyte necrosis.Apoptotic cells fail to promote inflammation and fail to releaseHMBG1 even after secondary necrosis, because of tight bindingof HMBG1 to chromatin. Blocking of chromatin hypoacetylationbefore induction of apoptosis suppresses HMGB1 binding tochromatin and promotes inflammation.

•• siRNA-directed inhibition of HIV-1 infection. Novina CD,Murray MF, Dykxhoorn DM, Beresford PJ, Riess J, Lee SK,Collman RG, Lieberman J, Shankar P, Sharp PA: Nat Med2002, 8:681-686.•• Short interfering RNA confers intracellular antiviralimmunity in human cells. Gitlin L, Karelsky S, Andino R:Nature 2002, 418:430-434.•• Modulation of HIV-1 replication by RNA interference.Jacque JM, Triques K, Stevenson M: Nature 2002, 418:435-438.Significance: In plants and insects, RNA interference (RNAi)protects cells from invasion by double-stranded RNA(dsRNA)-containing viruses by inducing rapid dsRNA degradation.

These three studies show for the first time that this innatedefence mechanism can be exploited in mammalian cells toinhibit viral entry and replication.Findings: Exogenous or endogenous dsRNA are rapidly cleavedinto 21–25 nucleotide small interfering RNA (siRNA). ThesesiRNA then promote rapid degradation of RNA with complementarysequences, which leads to post-transcriptional silencing of thecorresponding genes. Novina et al. show that siRNA targetingeither the HIV1-cellular receptor CD4 or the viral proteins Gag orNef inhibits HIV1 production by infected cells in vitro. Jacque et al.further demonstrate that siRNA targeting HIV1 inhibits both theearly and late steps of infection by inducing rapid degradation ofgenomic HIV1 RNA. Gitlin et al. show that siRNA specific to thepoliovirus genome markedly inhibits virus production in infectedhuman and mouse cells. In the latter study, the exquisitesequence specificity of the inhibition process, demonstrated bythe isolation of escape siRNA-resistant virus carrying a pointmutation within the targeted sequence, indicates that siRNA-mediated effects are attributed to RNAi rather than moredegenerate antisense or interferon-based mechanisms.

•• IRAK-M is a negative regulator of toll-like receptor signaling. Kobayashi K, Hernandez LD, Galán JE, Janeway CA,Medzhitov R, Flavell RA: Cell 2002, 110:191-202.Significance: Toll-like receptors (TLR) trigger inflammation following recognition of conserved molecular patterns shared byviral and bacterial pathogens. The TLR-induced signaling cascade that leads to inflammation includes several members ofthe highly conserved IL-1 receptor-associated kinase (IRAK)family. So far IRAK proteins, such as IRAK-1 and IRAK-4, havebeen shown to positively regulate the inflammatory cascade.This study identifies for the first time an intracellular negative regulator of inflammation called IRAK-M, which downmodulatesthe inflammatory signals induced by both TLR and IL-1 receptors.Findings: Macrophages from IRAK-M-deficient mice producehigher amounts of pro-inflammatory cytokines in response toTLR engagement, in comparison to their wild-type counterparts.These increased inflammatory responses are paralleled byincreased activation of the NF-κB transcription factor and stresskinases, which both contribute to inflammation. IRAK-M-deficientcells also show increased response to IL-1, a key amplifier ofinflammatory responses. In vivo, IRAK-M-deficient mice exhibitaltered lipopolysaccharide (LPS)-resistance, that is, primarychallenge of deficient mice to low doses of LPS (a ligand forseveral TLRs) does not protect them from toxic shock inducedby a secondary challenge with higher LPS doses.

• Hyporesponsiveness to vaccination with Borrelia burgdorferiOspA in humans and in TLR1- and TLR2-deficient mice.Alexopoulou L, Thomas V, Schnare M, Lobet Y, Anguita J,Schoen RT, Medzhitov R, Fikrig E, Flavell RA: Nat Med 2002,8:878-884.Significance: This study provides new insights into the role ofToll-like receptors (TLR) in lipoprotein recognition. It also estab-lishes for the first time a link between hyporesponsiveness tovaccination against some bacterial lipoproteins and TLRdefects in humans and rodents.Findings: Lyme disease is caused by the spirocheteBorrelia burgdoferi. Protective immunity against B. burgdofericorrelates with high titers of serum antibodies directed againstthe outer-surface lipoprotein (OspA), thus justifying the use ofrecombinant OspA as a vaccine against Lyme disease. Althoughthe OspA vaccine is effective in most individuals, about 5 % of

674 Paper alert

Innate immunity

vaccine recipients defined as low responders, develop very lowtiters of OspA-specific antibodies, which correlate with reducedinflammatory responses to OspA and decreased cell surfaceexpression of TLR1 in comparison to high responders. By con-trast, low responders show normal expression of TLR2, anothermember of the TLR family, which activates innate responses following recognition of lipoproteins. Consistent with a key roleplayed by TLR in efficient induction of humoral responsesagainst OspA, both TLR1- and TLR2-deficient mice showdecreased antibody responses against OspA in vivo, and theirmacrophages are unresponsive to OspA in vitro.

Selected by Juan Carlos Zúñiga-PflückerDepartment of Immunology, University of Toronto, Toronto, Canada

E-mail: jc.zuniga.pflucker@utoronto.ca

• A nonreduntant role for the adapter protein Shc in thymicT cell development. Zhang L, Camerini V, Bender TP,Ravichandran KS: Nat Immunol 2002, 3:749-755.Significance: This paper addresses the role of the adaptor protein Shc during T cell development. Although the role of Shcduring T cell activation had been previously investigated, its roleduring T cell development was unknown. This study providesclear evidence demonstrating that expression and phosphoryla-tion of Shc are essential for pre-TCR signaling and thus criticalfor further thymocyte differentiation.Findings: To address the role of Shc during T cell development,Ravichandran et al. employed a two-prong approach: they gener-ated Shc conditional knockout mice and transgenic mice thatconditionally express a dominant-negative form of Shc duringT cell development. Both approaches revealed that in the absenceof Shc function thymic cellularity was dramatically reduced andpre-TCR signaling was affected, as demonstrated by a block inthymocyte differentiation at the DN3 stage (CD44– CD25+). Thisblock in development is consistent with other pre-TCR signalingdefects. Of interest, IELs and T cells expressing the γδ TCR didnot appear to be affected by the loss of Shc function; however, themechanism responsible for this difference remains to beaddressed in addition to the precise nature of the signals down-stream of Shc phosphorylation during T cell development.

• Transcription from the RAG1 locus marks the earliestlymphocyte progenitors in bone marrow. Igarashi H,Gregory SC, Yokota T, Sakaguchi N, Kincade PW: Immunity2002, 17:117-130.Significance: This report identifies the earliest lymphocyteprogenitor population present in the bone marrow of adult mice.These cells are found within the c-kithi Sca-1hi Lin– subset ofbone marrow progenitors, and give rise almost exclusively to B,T and NK cells. In particular, commitment to the lymphocyte lineage appears to occur very soon after RAG-1 locus activationin c-kithi Sca-1hi Lin– cells.Findings: The earliest lymphocyte progenitors were identifiedby taking advantage of a RAG-1/GFP knock-in mouse model.Igarashi et al. identified GFP+ lymphoid-committed cells withinthe c-kithi Sca-1hi Lin– subset of the adult bone marrow. Thesecells did not appear to express the IL-7Rα chain, a marker thathas been previously used to identify common lymphocyte progenitors (CLPs). The authors also observed that GFP+ c-kithi

Sca-1hi progenitors can give rise to NK cells, suggesting that

RAG can be expressed prior to commitment to the NK cell lineage. A striking feature of the data is the observation thatwithin the c-kitlo Sca-1lo Lin- subset, where CLPs were firstdescribed, all of the B and T cell (and the majority of NK cell)differentiation potential was confined to GFP+ cells, which inkeeping with previous findings, also express the IL-7Rα chain.Thus, the ability to detect the activation of the RAG locus willallow further insights into the identity and composition of CLPswithin the bone marrow and other sites of lymphopoiesis.

Selected by Paul R WalkerUniversity Hospital Geneva, Geneva, Switzerland

e-mail: Paul.Walker@hcuge.ch

• Tumor-associated B7-H1 promotes T-cell apoptosis: a potential mechanism of immune evasion. Dong H,Strome SE, Salomao DR, Tamura H, Hirano F, Flies DB,Roche PC, Lu J, Zhu G, Tamada K et al.: Nat Med 2002, 8:793-800.Significance: Understanding the interaction of tumour cells withspontaneous and treatment-induced immune responses requiresan assessment of immunoregulatory molecule expression by thetumour. This paper adds tumour-expressed B7-H1 to an alreadysubstantial list of potentially immunosuppressive molecules. Findings: Costimulatory pathways for T cells involve positiveand negative regulation depending upon combinations of ligands and receptors. The recently described B7-H1 mole-cule can be immunostimulatory, particularly for Th2 immuneresponses, but it can also inhibit responses mediated by activated cytotoxic lymphocytes (CTLs). This study extendsprevious findings that B7-H1 mRNA can be expressed bytumours by immunohistochemical detection of the protein inseveral human cancer types. The functional significance of thisis suggested by apoptosis induction of human CTLs in vitro,and impaired antitumour CTL responses against B7-H1 trans-duced murine P815 tumour cells in vivo. Mechanisms wereinvestigated in some detail, with B7-H1-dependant CTL apop-tosis being partially reversed by neutralising antibodies to Fasligand and IL-10. Furthermore, the presence of a secondreceptor for B7-H1, distinct from the previously characterisedPD-1 receptor, was suggested by binding of B7-H1 to a PD-1negative clone and lack of inhibition of B7-H1 mediated effectsby B7-H1Ig.

• TCR-like human antibodies expressed on human CTLsmediate antibody affinity-dependent cytolytic activity.Chames P, Willemsen RA, Rojas G, Dieckmann D, Rem L,Schuler G, Bolhuis RL, Hoogenboom HR: J Immunol 2002,169:1110-1118.• Direct visualization of distinct T cell epitopes derived froma melanoma tumor-associated antigen by using humanrecombinant antibodies with MHC- restricted T cell receptor-like specificity. Denkberg G, Cohen CJ, Lev A, Chames P,Hoogenboom HR, Reiter Y: Proc Natl Acad Sci USA 2002,99:9421-9426.Significance: Antibodies recognising the ligands of tumourspecific CTLs (i.e. MHC bound peptide) have many potentialapplications in tumour immunology. These papers show thatsome of the hurdles for generating useful antibodies with speci-ficity for human cancer cells (low affinity, specificity for differentepitopes) can now be overcome.

Paper alert 675

Lymphocyte development

Tumour immunology

Findings: Both of these papers use antibodies derived fromphage libraries. The specificity of the Fab-G8 fragment used inthe study of Chames et al. was for an HLA-A1/MAGE-A1 epi-tope, a further antibody, Fab-Hyb3 was engineered from Fab-G8to have augmented affinity (without modification of fine speci-ficity) by in vitro affinity maturation. Human T cells transduced toexpress either of these antibodies at their surface recognisedtumour, but recognition was more efficient with Fab-Hyb-express-ing T cells (as assessed by cytotoxicity and TNF-α release). Thestudy by Denkberg et al. showed that it may also be possible todirectly select relatively high affinity antibodies from phage display. A panel of antibodies was produced that specificallyrecognised three different HLA-A2 complexed epitopes fromhuman melanoma differentiation antigen gp100. These antibodieswere used for the flow cytometric detection of HLA-2/gp100 epitopes on peptide-loaded antigen presenting cells as well ason melanoma cell lines constitutively expressing the antigen.

• Disease-associated bias in T helper type 1 (Th1)/Th2CD4+ T cell responses against MAGE-6 inHLA-DRB1*0401+ patients with renal cell carcinoma ormelanoma. Tatsumi T, Kierstead LS, Ranieri E, Gesualdo L,Schena FP, Finke JH, Bukowski RM, Mueller-Berghaus J,Kirkwood JM, Kwok WW et al.: J Exp Med 2002, 196:619-628.Significance: Th subset skewing of CD4+ T cell responses incancer patients has been previously reported, but unequivocaldemonstration of tumour antigen specificity was not alwaysachieved. This study compares Th profiles of CD4+ T cells specific for tumour-associated antigens and other antigens inrenal cell carcinoma and melanoma patients.Findings: Tatsumi et al. used IFN-γ and IL-5 ELISPOT assays,and TGF-β1 and IL-10 ELISAs to ascertain Th1, Th2 or Th3–/Trtype CD4+ peripheral blood T cell responses to MAGE-6derived epitopes, or Epstein-Barr- or influenza-derived epi-topes. Most patients with active disease had Th2 responses toMAGE-6 epitopes, but Th1 responses to the viral epitopes.Normal donors of the same DR type (DRB1*0401) and successfully treated patients showed either mixed Th1/Th2responses or Th1-biased immune responses to the Mage-6 epitopes. Significant TGF-β1 or IL-10 secretion was notdetected in any patients.

Selected by David EssayanUS Food and Drug Administration, Rockville, MD, USA

e-mail: essayan@cber.fda.gov

• Induction of NFATc2 expression by interleukin 6 promotesT helper type 2 differentiation. Diehl S, Chow C-W, Weiss L,Palmetshofer A, Twardzik T, Rounds L, Serfling E, Davis RJ,Anguita J, Rincón M: J Exp Med 2002, 196:39-49.Significance: Another important pathway for Th2 differentiation.Findings: T cells stimulated with anti-CD3 and anti-CD28 inthe presence of IL-6 underwent Th2 differentiation, producinglevels of IL-4 similar to T cells stimulated in the presence of IL-4.IL-6 enhanced NFAT transcriptional activity, but not the activityof AP-1 or NF-κB; anti-IL-6 abrogated the anti-CD3 andAPC-mediated increase in NFAT activity. Expression of a dominant-negative NFAT prevented IL-6-mediated IL-4 generationand differentiation of Th2 cells. Finally, these effects wereshown to be specific for NFATc2.

• T cell costimulation through CD28 depends on inductionof the Bcl-xγγ isoform: Analysis of Bcl-xγγ-deficient mice.Ye Q, Press B, Kissler S, Yang X-F, Lu L, Bassing CH,Sleckman BP, Jansson M, Panoutsakopoulou V, Trimble LAet al.: J Exp Med 2002, 196:87-95.Significance: A milestone in our understanding of the molecularbasis of CD28-dependent costimulation.Findings: Bcl-xγ expression is restricted to T cells and is upreg-ulated after T cell receptor and CD28 ligation. CD28 co-ligationof anti-CD3-stimulated T cells from Bcl-xγ-deficient mice failed toenhance T cell proliferation or IL-2 generation; conversely,enforced expression of Bcl-xγ replaced the costimulatory effectsof CD28 co-ligation. Deficient Bcl-xγ activity was associated withan IL-2-insensitive defect in cell cycle progression; enforcedexpression of Bcl-xγ replaced the effects of CD28 co-ligation oncell cycle progression. Unlike other Bcl-x family members, Bcl-xγdid not effect sensitivity to apoptosis. Finally, deficient Bcl-xγactivity was associated with reduced antigen-specific responsesin vivo and reduced generation of memory T cells.

• Changes in histone acetylation at the IL-4 and IFN-γγ lociaccompany Th1/Th2 differentiation. Fields PE, Kim ST,Flavell RA: J Immunol 2002, 169:647-650.• In Th2 cells the Il4 gene has a series of accessibilitystates associated with distinctive probabilities of IL-4 production. Guo L, Hu-Li J, Zhu J, Watson CJ, Difilippantonio MJ,Pannetier C, Paul WE: Proc Nat Acad Sci USA 2002,99:10623-10628.• Th cell differentiation is accompanied by dynamicchanges in histone acetylation of cytokine genes. Avni O,Lee D, Macian F, Szabo SJ, Glimcher LH, Rao A: Nat Immunol2002, 3:643-651.Significance: Elegant demonstrations of the hierarchical control of Th1/Th2 activation and effector functions at the levelof chromatin remodeling.Findings: Fields et al. demonstrated locus and lineage specificityof H3 and H4 acetylation (hyperacetylation of IL-4 under Th2 conditions and hyperacetylation of IFN-γ under Th1 conditions);differential, phenotype-specific acetylation patterns could bedetected as early as day six for IL-4 and day two for IFN-γ. Thisprocess was shown to be STAT-dependent with the use of STAT4and STAT6 knockout mice. Finally, transfection of GATA3 or Tbetinto STAT6- or STAT4-deficient T cells under Th2 or Th1 condi-tions, respectively, resulted in lineage-specific acetylation andcytokine secretion. Guo et al. demonstrated quantitative IL-4 pro-duction from stable Th2 clones to be a function of specific CpGmethylation and histone acetylation patterns, and not a function oftranscription factor levels. Moreover, patterns of CpG methylationand histone acetylation clearly distinguished Th2 clones from Th1clones. Low IL-4 producing clones, but not high IL-4 producingclones, increased IL-4 production when stimulated in the presenceof 5′-aza-2-deoxycytidine; Th1 clones did not acquire the capacityto produce IL-4. Finally, naïve T cells undergoing Th2 differentia-tion progressively developed the characteristic methylationpatterns of the model Th2 clones used in these experiments. Avniet al. demonstrated progressive changes in histone acetylationduring differentiation of naïve T cells to Th1 and Th2 cells.Changes in acetylation were more rapid at the Ifng locus than theIl4 locus. Hyperacetylation at the Il4 locus was STAT6 dependent,whereas hyperacetylation of the Ifng locus was T-bet dependent.

• Two distinct domains within the N-terminal region ofJanus kinase 1 interact with cytokine receptors. Usacheva A,

676 Paper alert

Lymphocyte activation and effector functions

Kotenko S, Witte MM, Colamonici OR: J Immunol 2002,169:1302-1308.Significance: Janus kinase 1 (Jak1) uses different domains tointeract with different cytokine receptors, suggesting the poten-tial for cytokine signaling specificity at the level of Jaks.Findings: Jak1 is comprised of 7 Jak homology domains, designated JH1–JH7 starting at the carboxyl terminus of themolecule. Deletion of the amino terminus of Jak1 (JH7–JH6)impaired binding to IL-2Rβ and IL-4Rα, but did not impair binding to IFNαRβL or IL-10Rα. However, deletion of JH7–JH6abrogated kinase activation.

• Two-step binding mechanism for T-cell receptor recognitionof peptide-MHC. Wu LC, Tuot DS, Lyons DS, Garcia KC, Davis MM: Nature 2002, 416:552-556.Significance: A tour-de-force demonstration of the physicalbasis for T cell scanning of peptide–MHC by TCR.Findings: Utilizing plasmon resonance measurements of theinteraction of the 2B4 TCR with an extensive panel of peptideand MHC mutants of the moth cytochrome c peptide(residues 88–103) presented in IEk, the authors showed thatMHC contacts dominated initial association with TCR butcontributed little to stabilization of this interaction, whereaspeptide contacts contributed to stabilization of TCR associa-tion through the effects on off-rates of binding, but had littleeffect on initial association. This suggests an initial short duration (low affinity) interaction of TCR with MHC that ismostly peptide independent (scanning), followed by a longerduration (higher affinity) interaction that is peptide dependentand imparts ‘antigen specificity’ to signaling interactions.Finally, peptide recognition was demonstrated to occurthrough the CDR3 loop.

Selected by Nicolas GlaichenhausInstitut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France

e-mail: glaichenhaus@ipmc.cnrs.fr

•• Multiple Chlamydia pneumoniae antigens prime CD8+

Tc1 responses that inhibit intracellular growth of this vacuolar pathogen. Wizel B, Starcher BC, Samten B,Chroneos Z, Barnes PF, Dzuris J, Higashimoto Y, Appella E,Sette A: J Immunol 2002, 169:2524-2535.Significance: Chlamydia pneumoniae (Cpn) is a common causeof pneumonia, bronchitis, pharingitis and sinusitis in humans.Although CD8+ T cells play a critical role in immunity to Cpn, thetarget antigens recognized by Cpn-specific CD8+ T cells havenot been identified and the mechanisms by which these T cellscontributes to protection remained unknown. This study providessome insights into these issues and lays the foundation for futurework to develop vaccines against Cpn infections.Findings: Wizel et al. found that Cpn-infected mice generatedpathogen-specific CD8+ T cells which exhibit both cytotoxicactivity and the ability to secrete interferon (IFN)-γ. They prepared cytotoxic CD8+ T cell lines from infected mice andshowed that these T cells could suppress chlamydial growthin vitro both by direct lyses of Cpn-infected macrophages andby secretion of IFN-γ. The authors also identified 18 peptideswhich were derived from 12 different Cpn proteins and whichcould sensitize target cells for MHC-class I-restricted killing byCD8+ T cells from infected mice.

•• K3-mediated evasion of CD8+ T cells aids amplificationof a latent gamma-herpesvirus. Stevenson PG, May JS,Smith XG, Marques S, Adler H, Koszinowski UH, Simas JP,Efstathiou S. Nat Immunol 2002, 3:733-740.Significance: The murine γ-herpesvirus-68 (MHV-68) is a natural γ2-herpesvirus of small rodents that has homology tothe Kaposi’s sarcoma-associated herpesvirus (KSHV) andEpstein-Barr virus (EBV). Following intranasal administration,MHV-68 is rapidly cleared from the lungs but spreads to lym-phoid tissues where it establishes latency in B lymphocytes,macrophages and dendritic cells (DCs). In this paper, theauthors describe a new mechanism by which MHV-68 evadesthe immune response. This work paves the road for the devel-opment of attenuated viruses which could be used as vaccinesagainst herpesvirus diseases in humans.Findings: K3 is a viral protein which is expressed in lymphoidtissues during latency, and which is conserved in differentγ2-herpesviruses. To determine whether K3 plays a role inimmune evasion, Stevenson et al. constructed a K3-deficientMHV-68 mutant and tested its ability to infect mice. Althoughboth wild type (wt) and K3-deficient viruses were rapidlycleared from the lungs of infected animals, mice infected withK3-deficient viruses exhibited much lower viral loads than thoseinfected with wt viruses several weeks after infection. Reducedviral loads in mice infected with K3-deficient viruses correlatedwith increased virus-specific cytotoxic T cell responses, furthersuggesting that CD8+ T cells were responsible for the eliminationof K3-deficient viruses. This hypothesis was later confirmed bydepleting CD8+ T cells in vivo. Thus, K3 allows MHV-68 toevade CTL eventually providing an increased window forlatency establishment.

• Cross-presentation of Listeria monocytogenes-derivedCD4 T cell epitopes. Skoberne M, Schenk S, Hof H,Geginat G. J Immunol 2002, 169:1410-1418.Significance: Listeria monocytogenes is an intracellular bacteriawhich is able to escape the endosomal compartment and toenter the cytosol of the host cell. Although the T cell immuneresponse against L. monocytogenes is dominated by CD8+

T cells, infected animals also mount a CD4+ T cell response.This study provides new information on L. monocytogenes-specific CD4+ T cells and on the mechanisms which lead to theprocessing and the presentation of MHC class II-restrictedbacterial epitopes in vivo.Findings: The authors first found that L. monocytogenes-specificCD4+ and CD8+ T cells expanded synchronously between daythree and day ten after infection. Using an in vitro presentationassay, they further showed that L. monocytogenes-derived CD4+

T cell epitopes were efficiently presented by dendritic cells (DCs)in vivo. Infected DCs or macrophages were poorly efficient atstimulating L. monocytogenes-specific CD4+ in vitro. However,non-infected DCs were very efficient at presenting bacterial antigens when incubated with L. monocytogenes-infected DCsor macrophages. This strongly suggested that cross-presentationrather than direct presentation was involved in the processing ofL. monocytogenes-derived MHC class II epitopes.

• Rapid expansion and IL-4 expression by Leishmania-specific naive helper T Cells in vivo. Stetson D, Mohrs M,Mallet-Designe V, Teyton L, Locksley R: Immunity 2002,17:191-200.Significance: Leishmania major is an intracellular parasitewhich infects macrophages. Although previous experiments

Paper alert 677

Immunity to infection

had shown that L. major induces a strong CD4+ T cellresponse, very little was known about the kinetics of T cell differentiation in vivo. In this paper, Stetson et al. shed new lighton this issue by studying the emergence of IL-4-expressingcells during the course of the infection.Findings: To enumerate IL-4-expressing cells, Stetson et al.used transgenic mice (4get) in which cells that express IL-4accumulate enhanced Green Fluorescent Protein (eGFP) intheir cytoplasm. Mice were infected with L. major and CD4+

T cells were analyzed by flow cytometry following staining withMHC class II-tetramers which were specific for CD4+ T cellsreacting to the parasite immunodominant LACK antigen.Results showed that LACK-specific CD4+ T cells differentiatedinto IL-4-secreting cells as early as three days after infection.Differentiation occurred in the draining lymph nodes of infectedanimals and was observed in both susceptible BALB/c (H2-d)and resistant B10.D2 (H2-d) mice.

•• Hyporesponsiveness to vaccination withBorrelia burgdorferi OspA in humans and in TLR1- andTLR2-deficient mice. Alexopoulou L, Thomas V, Schnare M,Lobet Y, Anguita J, Schoen RT, Medzhitov R, Fikrig E,Flavell RA: Nat Med 2002, 8:878-884.Significance: Lyme disease is caused by the spirocheteBorrelia burgdorferi. The outer-surface lipoprotein (OspA) ofB. burgdorferi is one of the most abundant antigens on spiro-chetes. Previous studies had shown that active immunizationwith recombinant OspA protects mice from Lyme borreliosis andthat protective immunity in humans correlates with the develop-ment of high titer antibodies against OspA. Despite theseresults, the molecular mechanisms which allowed infected orimmunized individuals to mount a vigorous immune responseagainst OspA remained to be elucidated. This paper providesnew and unexpected information on this important issue.Findings: Out of 492 individuals which had been vaccinated withan OspA-based vaccine, Alexopoulou et al. identified seven vaccine recipients who exhibited very low titers of anti-OspA antibodies one month after immunization. Further experimentsshowed that macrophages from these low responders expressedlow levels of the Toll-like receptor (TLR)-1. Furthermore, TLR-1-deficient mice produced low titers of anti-OspA antibodies followingimmunization with recombinant OspA. These results demonstratea critical role of TLR-1 in OspA recognition and show that defectsin TLR-1 can abrogate the response to OspA-based vaccines.

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

e-mail: anna.vyakarnam@kcl.ac.uk

• A balanced type 1/type 2 response is associated withlong-term nonprogressive human immunodeficiency virustype 1 infection. Imami N, Pires A, Hardy G, Wilson J,Gazzard B, Gotch F: J Virol 2002, 76:9011-9023.Significance: The nature of immune responses that correlate withnon-progression following HIV infection remain controversial. Thispaper shows that non-progression is associated with specificT cell type 1 (IL-2, IFN-γ) as well as type 2 (IL-4) responses.Findings: Non-progressors (NPs) had strong proliferative andIL-2 responses to recall antigens, HIV proteins and several epitopes in HIV-1 gag p24. NPs also had an IL-4 response tomany HIV proteins and to a limited number of Gag p24 epitopes.Unlike the IL-2 response, the strength and breadth of the proliferativeresponse did not correlate with IL-4 production. In treatment-naïveprogressors who had a falling CD4+ count with a low virus load,

a more focused specific response was detected that wasrestricted mainly to Gag p24. Proliferative and IL-2 responses toHIV-specific and recall antigens in such subjects was lower thanin NPs. These patients lacked a specific IL-4 response as mea-sured RT-PCR or by proliferation of a cell line that respondedspecifically to IL-4. However, a longitudinal study of one subjectbefore and after progression to symptomatic disease showed adecline in proliferation and IL-2 production and a rise in IL-4 secretionto all antigens tested. Although this by no means is evidence of atype 1–type 2 switch with disease progression in HIV infection,the paper does provide evidence that NPs have a balanced type1 and type 2 specific response. This differs from earlier studiesthat failed to detect specific IL-4 responses in NPs.

• CD4 T cell depletion is linked directly to immune activation in the pathogenesis of HIV-1 and HIV-2 but only indirectly to the viral load. Sousa AE, Carneiro J,Meier-Schellersheim M, Grossman Z, Victorino RM: J Immunol2002, 169:3400-3406.Significance: The extent to which CD4+ depletion in HIV infectionis a result of increasing virus load or other parameters, such as immune activation, continues to be debated. This study contributes to this debate by showing that CD4+ number correlates directly with immune activation but only indirectlywith virus replication rate.Findings: HIV-1 and HIV-2 patients with a similar degree of CD4+

depletion but with differing virus loads were compared. The virusload of the HIV-2 group was two orders of magnitude lower thanthe HIV-1 group. Several immune activation markers (HLA-DR,CD38, CD69 and Fas molecules) were expressed at similar levelsin both groups of subjects. In addition, the level of T cell anergy asassessed by proliferative responses to CD3 stimulation and to apanel of microbial antigens was similarly lower in the two patientgroups compared to HIV uninfected control subjects. A similarincrease in the number of Ki67+ cycling CD4+ T cells, which cor-related directly with immune activation markers, was also noted inboth groups of subjects compared to HIV negative controls. Thedata support the hypothesis that immune activation, rather thanvirus load, directly drives CD4+ cell depletion. The authors arguethat the underlying difference in virus load, but not CD4+ depletionor immune activation between HIV-1 and HIV-2 patients, may becaused by host factors that restrict HIV-2 replication rate. Whilstthis might significantly reduce HIV-2 transmission, it may notimpact on immune activation as immune activation is related toHIV-mediated enhancement of antigen presenting cell–lympho-cyte interactions rather than the amount of free virus produced.Such a scenario, if proven, would explain the slower rate of progression of HIV-2 compared to HIV-1 infection and why substantially lower virus load in HIV-2 infection is associated withlevels of immune activation and CD4+ depletion similar to thoseseen in HIV-1 infection.

Selected by Jean-Laurent CasanovaLaboratory of Human Genetics of Infectious Disease, Necker-Enfants

Malades Medical School, Paris, Francee-mail: casanova@necker.fr

• Mutations in the gene encoding the lamin B receptor produce an altered nuclear morphology in granulocytes(Pelger Huet anomaly). Hoffmann K, Dreger CK, Olins AL,

678 Paper alert

Immunogenetics

Olins DE, Shultz LD, Lucke B, Karl H, Kaps R, Muller D,Vaya A et al.: Nat Genet 2002, 31:410-414.Significance: This paper reports the identification of the molecular basis of inherited Pelger-Huët anomalyFindings: The Pelger-Huët anomaly (PHA) of granulocytes isinherited as a benign autosomal dominant trait that consists ofbi-lobulated neutrophil nuclei with coarse chromatin. Homozygousindividuals have a more severe phenotype with round neutrophilnuclei as well as lesions of the bones and central nervous system.Following a positional cloning approach in an ethnic group wherePHA prevalence reaches 1%, instead of the 0.1–0.01% preva-lence world-wide, the authors identified a locus on 1q41–43.Mutations were found in the gene encoding the lamin B receptor(LBR), a member of the sterol reductase family; there was only halfthe normal amount of LBR protein in heterozygotes and traceamounts in homozygotes. The LBR is an integral protein of theinner nuclear membrane. The elucidation of the molecular basis forPHA reveals that the LBR plays a dose-dependent role in nuclearshape and chromatin distribution in granulocytes. This study pavesthe way for a better understanding of the basic mechanisms ofnuclear envelope–chromatin interaction as well as of the patho-genesis of acquired forms of Pelger-like abnormalities.

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

e-mail: liu-3@medctr.osu.edu

•• Modulation of TCR-induced transcriptional profiles by ligation of CD28, ICOS, and CTLA-4 receptors. Riley JL, Mao M,Kobayashi S, Biery M, Burchard J, Cavet G, Gregson BP, June CH,Linsley PS: Proc Natl Acad Sci USA 2002, 99:11790-11795.•• Genomic expression programs and the integration of theCD28 costimulatory signal in T cell activation. Diehn M,Alizadeh AA, Rando OJ, Liu CL, Stankunas K, Botstein D,Crabtree GR, Brown PO: Proc Natl Acad Sci USA 2002,99:11796-117801.Significance: These studies represent the first systematic profiling of genes augmented by costimulatory molecules, theimportant targets of immunotherapy. The results provide a mostvaluable global picture on the biological significance and integration of costimulatory signals.Findings: Both studies found that instead of inducing de novogene transcription, anti-CD28 or B7-1/2 molecules primarilyaugment transcription of genes induced by anti-CD3 mAbs.Riley et al. reported that ICOS and CD28 enhanced expressionof similar genes. Surprisingly, anti-CTLA4 mAb does not shutdown the expression of genes induced by anti-CD3, althoughthe antibody reduces the function of anti-CD28. Diehn et al.found that, among the genes that are most enhanced are theknown targets of nuclear factor of activated T cells (NFAT) transcription factors. These findings support the notion thatCD28 signaling is integrated at the level of NFAT.

•• Tumor-associated B7-H1 promotes T-cell apoptosis: a potential mechanism of immune evasion. Dong H,Strome SE, Salomao DR, Tamura H, Hirano F, Flies DB, Roche PC,Lu J, Zhu G, Tamada K et al.: Nat Med 2002, 8:1039-800.Significance: The authors illustrate that the new member of B7family augment apoptosis of T cells and can be used by tumorcells to evade host immunity.

Findings: The authors found that B7-H1 is absent from normal,non-hematopoietic cells. However, it is widely expressed onmalignant cells, including clinical cancerous tissues.B7-H1-expressing cells avoid cytolysis by inducing apoptosisof cytolytic T cells. This can be achieved by PD-1-dependentand PD-1-independent mechanisms.

Selected by Hugh Auchincloss Jr, Gerry Waneck and Christian LeGuernMassachusetts General Hospital, Boston, MA, USA

e-mail: auchincl@helix.mgh.harvard.edu

•• Memory CD8(+) T cells undergo peripheral tolerance.Kreuwel HT, Aung S, Silao C, Sherman LA: Immunity 2002,17:73-81.Significance: CD8+ memory T cells have long been considered acell subset refractory to tolerance induction because of theirprompt reactivity to cognate antigens. The present study estab-lishes that memory cells, generated by two different tolerogenicregimens, are as susceptible to tolerance as naïve effector T cells.These important findings should lead to improved immunotherapyprotocols for tolerance induction in all T cell compartments.Findings: Adult transgenic mice selectively expressing thehemagglutinin (HA) of the influenza virus in the pancreas are tolerant to HA. Injection of soluble HA peptides or immunizationwith the virus (cross-presentation of HA peptides on host APC)recruited CD8+, CD25int, CD62Lhigh, CD69neg, Ly-6Chigh

memory T cells, which showed peripheral tolerance. Contrary tonaïve CD8+ T cells tolerant to HA, tolerant memory CD8+

T cells produced IFN-γ upon activation. Both memory and naïveT cell tolerance proceeded through the same mechanisms,including abortive cell activation and division.

• Characterization of a new subpopulation of mouseCD8alpha+ B220+ dendritic cells endowed with type 1 interferon production capacity and tolerogenic potential.Martin P, Del Hoyo GM, Anjuere F, Arias CF, Vargas HH,Fernandez LA, Parrillas V, Ardavin C: Blood 2002, 100:383-390.Significance: The characterization of tolerogenic dendritic cell(DC) populations is still controversial and the mechanism of tolerance induction by these cells is unknown. This studydescribes a new murine DC subtype exhibiting the features ofimmature DC with dual functions: in the immature stage theypromote the differentiation of regulatory T cells (Treg), whereasas mature DCs they stimulate Th1 responses. Although thedirect implication of Tregs in the tolerance mechanism remainsto be established, these data clearly define a cell subpopulationwith great potential for tolerance induction therapy.Findings: B220+, MHC class Illow, CD11cint cells represent aminute population of immature DCs, which were isolated in thisstudy from the thymus, bone marrow, spleen and lymph nodes.B220+ DCs can differentiate into class IIhigh, IFN-α+, IL-10 andIL-12-producing mature DCs upon antigen activation. Contraryto mature DCs, immature B220+ DCs promoted inhibition ofT cell clone proliferation in vitro, probably through Treg activation,as this could not be reverted by the addition of IL-2.

•• Infectious tolerance: human CD25(+) regulatory T cellsconvey suppressor activity to conventional CD4(+) T helpercells. Jonuleit H, Schmitt E, Kakirman H, Stassen M, Knop J,Enk AH: J Exp Med 2002, 196:255-260.

Paper alert 679

Immunotherapy

Transplantation

Significance: The mechanism of Treg-mediated suppressionremains unclear in particular on the requirement for cell contactand/or cytokines, such as TGF-β1, in suppression. The resultsfrom this study support the reconciling view that Tregs wouldanergize, via cell–cell contacts, a first set of conventional Th1CD4+ cells, which in turn inhibit the activation of freshly isolatedT helper cells via TGF-β1. the authors describe a convincingset of data which provides a molecular basis to the spreadingor infectious tolerance phenomenon.Findings: Using in vitro suppression coculture assays thatinvolved purified CD4+CD25+ Tregs, and CD25neg Th stimulatedeither by anti-CD3 mAb or allogeneic DCs, the authors demon-strated first that the initial suppressive activity of Tregs on freshlyactivated Th cells required cell contact, but not membrane boundTGF-β; second that Treg suppressive activity also required pro-tein synthesis; third that ‘suppressed’ Th cells, when depleted ofTregs, were still able to inactivate freshly stimulated Th cells; andfourth, This Treg independent suppression did not necessitatecell contact and was in part mediated by soluble TGF-β1.

•• Donor-type CD4+CD25+ regulatory T cells suppresslethal acute graft-versus-host disease after allogeneic bonemarrow transplantation. Hoffmann P, Ermann J, Edinger M,Fathman CG, Strober S: J Exp Med 2002, 196:389-399.Significance: This study demonstrates that freshly isolatedCD4+CD25+ cells (Tregs) from unprimed mice can preventlethal graft-versus-host-disease (GVHD) induced byCD4+CD25– T cells after allogeneic transplantation across acomplete MHC class I and II barrier, and that the outcomedepends on the balance between these two T cell populations.Findings: CD4+CD25+ Tregs isolated from naïve C57BL/6spleen or bone marrow suppressed the in vitro proliferativeresponse of syngeneic CD4+CD25– T cells to allogeneicBALB/c stimulators. When these two T cell populations weremixed at a ratio of 1:1, Tregs protected lethally irradiatedBALB/c recipients from acute GVHD, whereas a 1:10 ratio(similar to that found in the spleen of normal C57BL/6 mice) didnot protect. The ability to protect from GVHD, but not to sup-press the in vitro proliferative response, was abrogated whenTregs were derived from IL-10–/– mice. Suppression/protectionrequired Tregs that were derived from responder/donor origin.

•• Generation of histocompatible tissues using nucleartransplantation. Lanza RP, Chung HY, Yoo JJ, Wettstein PJ,Blackwell C, Borson N, Hofmeister E, Schuch G, Soker S,Moraes CT et al.: Nat Biotech 2002, 20:689-696.Significance: This study demonstrates that, despite concernsthat mitochondrial DNA might encode minor histocompatibilityantigens, nuclear transfer technology can be used to generatehistocompatible tissue from stem cell precursors.Findings: The investigators performed nuclear transfer frombovine fibroblasts to oocytes. Various tissues were subsequentlyobtained from 5–8 week old fetuses derived from the resultingblastocysts. Analysis of cell lines from these tissues indicatedthat their mitochondrial genes did have nucleotide substitutionsdetermined by the oocyte rather than the nuclear donor, and thatthese substitutions might generate minor histocompatibility anti-gens. Nonetheless, tissues engineered from these lines werenot rejected when they were transplanted into the nuclear donor.

• Modulation of tissue-specific immune response to cardiac myosin can prolong survival of allogeneic hearttransplants. Fedoseyeva EV, Kishimoto K, Rolls HK,

Illigens BM-W, Dong VM, Valujskikh A, Heeger PS,Sayegh MH, Benichou G: J Immunol 2002, 169:1168-1174.• Evidence for immune responses to a self-antigen in lungtransplantation: role of Type V collagen-specific T cells inthe pathogenesis of lung allograft rejection. Haque MA,Mizobuchi T, Yasufuku K, Fujisawa T, Brutkiewicz RR, Zheng Y,Woods K, Smith GN, Cummings OW, Heidler KM, Blum JS,Wilkes DS: J Immunol 2002, 169:1542-1549.Significance: These two papers provide further evidencethat autoimmune responses participate in the rejection ofallogeneic tissues.Findings: In the first study, the authors administered cardiacmyosin, a major contractile protein of the heart, in incompletefreund’s adjuvent (IFA) to mice before allogeneic cardiac trans-plantation. This treatment with an autoantigen often led toindefinite graft survival of MHC class I disparate allografts. Inthe second study, the authors generated T cell lines specific fortype V collagen from lymphocytes in lung allografts undergoingrejection. These lines did not respond to alloantigens. Lineswith this specificity could not be generated from lymphocytesfrom normal lungs. Adoptive transfer of these autoreactive linesdid not cause pathologic changes in normal syngeneic lungs,but did cause changes in lung isografts.

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

e-mail: akdisac@siaf.unizh.ch

• Association of the ADAM33 gene with asthma and bronchialhyperresponsiveness. Van Eerdewegh P, Little RD, Dupuis J,Del Mastro RG, Falls K, Simon J, Torrey D, Pandit S, McKenny J,Braunschweiger K et al.: Nature 2002, 418:426-430.Significance: Asthma is an increasingly common disease thatafflicts hundreds of millions of people world-wide. It is a genetically heritable, complex disorder that requires exposureto certain environmental factors before it is fully expressed. Theidentification and characterization of ADAM33, a putativeasthma susceptibility gene provides insights into the patho-genesis and natural history of this common disease.Findings: ADAM proteins are membrane-anchored metallo-proteinases with diverse functions, which include the sheddingof cell-surface proteins such as cytokines and cytokine recep-tors. The authors have performed genome-wide scan on 460Caucasian families and identified a locus on chromosome20p13, which occurred about 1 000 times more often in asth-matic siblings. This particular DNA signature showed a further10 times increased linkage to bronchial hyperresponsiveness.A survey of 135 polymorphisms in 23 genes identified that theADAM33 gene is significantly associated with asthma andbronchial hyperresponsiveness.

• Direct effects of interleukin-13 on epithelial cells causeairway hyperreactivity and mucus overproduction inasthma. Kuperman DA, Huang X, Koth LL, Chang GH,Dolganov GM, Zhu Z, Elias JA, Sheppard D, Erle DJ: Nat Med2002, 8:885-889.Significance: Asthma is mediated by T lymphocytes, whichproduce a T helper 2-like cytokine profile including IL-4, IL-5,IL-9 and IL-13. IL-13 is apparently the most critical of thesecytokines, because blockage of IL-13 markedly inhibits

680 Paper alert

Allergy and hypersensitivity

allergen-induced airway hyperreactivity, mucus production andeosinophilia in mice. In addition, IL-13 delivery to airwayscauses typical asthma-like inflammation demonstrating thatIL-13 is both necessary and sufficient for experimental modelsof asthma. This study demonstrates that IL-13 plays a major rolein asthma with direct effects on bronchial epithelial cells.Findings: Signal transducer and activator of transcription 6(STAT6) is a critical signaling molecule activated by IL-13 andis essential for the development of allergen-induced experimentalasthma. Mice lacking STAT6 were protected from all pulmonaryeffects of IL-13. Reconstitution of STAT6 only in bronchialepithelial cells was sufficient for IL-13-induced airway hyper-reactivity and mucus production. Interestingly, these mice didnot show any lung inflammation or other lung pathology,demonstrating the direct effect of IL-13 on bronchial epithelialcells in causing two essential features of asthma.

Selected by Allison GreenCambridge Institute for Medical Research, Addenbrooke’s Hospital,

Cambridge, UKe-mail: allison.green@cimr.cam.ac.uk

•• Antigen-specific regulatory T cells develop via theICOS–ICOS ligand pathway and inhibit allergen-inducedairway hyperreactivity. Akbari O, Freeman GJ, Meyer EH,Greenfield EA, Chang TT, Sharpe AH, Berry G, DeKruyff RH,Umetsu DT: Nat Med 2002, 8:1024-1032.Significance: Although this selection is not strictly autoimmunityrelated, the identification of molecular interactions that impacton the development of regulatory T cells (Tregs) is of impor-tance to transplantation, cancer and autoimmunity researchers.Here, the authors provide evidence that regulatory T cell devel-opment and function is dependent on the co-stimulatorypathway ICOS–ICOS ligand.Findings: Respiratory exposure to allergens causes initial expan-sion of allergen-specific CD4+ T cells followed by either deletionof these T cells or T cells that are resistant to re-stimulation.Intranasal (i.n.) administration of OVA resulted in IL-10-producingDCs in the bronchial lymph nodes. These DCs induced the devel-opment of IL-10-secreting, but not IL-4-secreting CD4+ Tregsfollowing repeated stimulation in vitro. Adoptive transfer of thesein vitro-generated Tregs into OVA-sensitized mice potently inhibited airway hyperreactivity (AHR). This suppression could beabrogated by the dual administration of anti-IL-10 neutralizing Abswith Tregs. Control transfers of IL-10-producing Th2 cells did notsuppress AHR. Through a series of transfer experiments, Tregswere shown to suppress AHR by decreasing IL-4 production andincreasing IL-10 production by endogenous OVA-specific CD4+

Th2 cells as well as inhibiting OVA-specific T cell proliferation.Blockade of ICOS–ICOS ligand interactions prevented the devel-opment of Tregs both in vitro and in vivo; in this latter case,OVA-sensitized mice developed AHR due to decreased IL-10 andincreased IL-4 production by OVA-specific CD4+ T cells. FACSanalysis demonstrated that DCs in tolerized mice expressed ICOSligand whereas OVA-specific CD4+T cells expressed ICOS andthis level of expression was maintained for several weeks. Micethat were not tolerized expressed significantly less ICOS on theirT cells. Finally, if DCs that had been induced by i.n. immunizationof OVA were pulsed with OVA in the presence of absence of anti-ICOS ligand Abs, only the latterly-treated DCs could inhibit AHR.

• Bacteria-triggered CD4+ T regulatory cells suppressHelicobacter hepaticus-induced colitis. Kullberg MC,Jankovic D, Gorelick PL, Caspar P, Letterio JJ, Cheever AW,Sher A: J Exp Med 2002, 196:505-515.Significance: Infection of IL-10 knockout (KO) mice withHelicobacter hepaticus results in colitis, whereas similar infection of wild-type (WT) mice does not. Here, the authorsdemonstrate that in a model of colitis, Treg elicitation and function is antigen specific. Furthermore, these cells reside predominantly in the CD45RBlowCD25–CD4+ T cell fraction ofthe mesenteric lymph nodes following bacterial infection.Findings: Transfer of CD4+ T cells from IL-10 KO mice intoH. hepaticus-infected RAG KO mice resulted in colitis. In contrast, similar transfers into non-infected RAG KO mice didnot induce intestinal inflammation suggesting H. hepaticusinfection was linked to the development of intestinal aggressiveCD4+ T cells. Dual transfer of CD4+ T cells from IL-10 KOmice with mesenteric lymph node (MLN)-derived CD4+ T cellsfrom H. hepaticus-infected WT mice, into RAG KO miceinfected with H. hepaticus prevented colitis, whereasMLN-derived CD4+ T cells from un-infected WT mice wereincapable of controlling colitis development. Interestingly, thesingle transfer of MLN-derived CD4+ T cells from non-infectedmice induced colitis in RAG KO recipients, whereas no intestinalinflammation resulted in mice receiving cells from infecteddonors. Taken together these findings suggested that Tregscapable of preventing colitis are elicited following H. hepaticusinfection, thereby implying that Tregs are antigen specific.Although these Tregs resided in both the CD45RBlowCD25–

and CD45RBlow CD25+ fractions of MLN-derived CD4+

T cells in infected mice, the CD45RBlowCD25– cells was morepotent. Both types of Tregs required IL-10 but not TGF-β topromote their inhibitory functions.

• Memory CD8+ T cells undergo peripheral tolerance.Kreuwel HTC, Aung S, Silao C, Sherman LA: Immunity 2002,17:73-81.Significance: Memory T cells respond more rapidly to antigenthan naïve T cells. It is unclear therefore whether memoryCD8+ T cells are capable of being tolerized. Here the authorsdemonstrate that memory CD8+ T cells are as susceptible to tolerance induction as naïve CD8+ T cells. This could haveimportant implications in designing new therapeutics tocounter autoimmunity.Findings: Infection of 14-day old transgenic mice expressinginfluenza virus haemaglutinin (HA) on the β-cells with influenzavirus results in rapid diabetes development in 50% of infectants. Mice that remained diabetes free showeddecreased cytotoxic T lymphocyte (CTL) responses to HA asthey aged suggesting HA-specific memory CD8+ T cellsbecome tolerized. Such tolerance induction could be inducedby a combination of infection and administration of soluble HA-peptide. Using an adoptive transfer model and CFSE-labeled naïve or memory HA-specific CD8+ TCR T cells, bothnaïve and memory HA-specific CD8+ T cells proliferated withequal magnitude in the pancreatic lymph nodes (PLNs).Following this initial proliferation, HA-specific CD8+ T cell numbers decreased and failed to infiltrate islets, irrespective ofthe CD8+ T cell’s activation status suggesting memory cellsbehave like naïve cells upon tolerization. This hypothesis wasfurther substantiated by demonstrating that the rate of tolerance induction for both naïve and memory CD8+ T cells isdependant on the concentration of their cognate antigen.

Paper alert 681

Autoimmunity