625

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 2001, 13:625–633

Selected by Tim ElliottUniversity of Southampton, Southampton, UK

e-mail: tje@soton.ac.uk

• An endoplasmic reticulum protein implicated in chaper-oning peptides to major histocompatibility of class I is anaminopeptidase. Menoret A, Li Z, Niswonger ML, Altmeyer A,Srivastava PK: J Biol Chem 2001, 276:33313-33318.Significance: There is a growing list of enzymes that are capableof trimming precursors of T-cell epitopes in the endoplasmic retic-ulum (ER). For some epitopes, this trimming may be obligatory.Gp96 is the most abundant ER-resident protein and has beenshown to bind to peptides delivered there by TAP. It is thereforea candidate cofactor for the assembly of class I molecules withantigenic peptides. The fact that peptides bound to gp96 can betaken up by antigen-presenting cells using the CD91 receptor isinteresting and may mean that precursor epitopes could betrimmed in compartments other than the ER, following receptor-mediated uptake of gp96 into mildly acidic endosomes.Findings: This group has followed up a chance observation,that apparently pure preparations of the heat-shock proteingp96 underwent autolysis upon storage. They have gone on totrace this phenomenon to an aminopeptidase actvity in thegp96 protein itself which is inhibited by classic aminopeptidaseinhibitors like bestatin and amastatin as well as the serine-protease inhibitor PMSF. This latter observation led them toshow that the aminopeptidase activity resided at least in part ina serine-protease-like motif GWSG at positions 653−656. Thecalcium-dependent activity (which is maximal with the syntheticsubstrate gly-phe p-nitroanilide at pH 6.5) is not shared by thehomologous heat-shock protein hsp90 or the unrelated hsp70.

Although the activity is very low compared with otheraminopeptidases (eg it is around 5 x 106 times less active thanmicrosomal alanyl aminopeptidase), it was shown to effectivelytrim 11 amino acids from the amino terminus of a precursorT-cell epitope when added in equimolar concentration to aT-cell readout assay.

• Differences in the expression of human class I MHC alle-les and their associated peptides in the presence ofproteasome inhibitors. Luckey CJ, Marto JA, Partridge M,Hall E, White FM, Lippolis JD, Shabanowitz J, Hunt DF,Engelhard VH: J Immunol 2001, 167:1212-1221.Significance: The relative contributions of different proteolyticpathways to the generation of MHC class I restricted T cell epi-topes are poorly understood. The finding that different class I allelescan draw on a non-proteasomal pathway to different extents allowsus to entertain the possibility of inhibiting the generation of certainepitopes (which may be associated with harmful pathogenesis)without inhibiting global intracellular protein turnover.Findings: Stripping cell-surface class I molecules of peptidesusing low-pH buffers destabilises them, causes them to denatureand induces their catabolism. Re-expression of new class I molecules at the cell surface is dependent on the intracellulargeneration of peptide epitopes. Using this observation, Luckey etal. have evaluated the degree to which proteasomes are respon-sible for generating these peptides by measuring re-expression of13 class I alleles in the presence of general (LLnL) and specific(lactacystin and z-LLL vinyl sulphone) proteasome inhibitors. Theyfound that although the inhibitors were able to block proteasomeactivity by up to 99%, they affected class I re-expression in anallele-dependent way, with re-expression of some (e.g. HLA-A1)inhibited by 80% and others (e.g. HLA-B2705) inhibited by as lit-tle as 10%. This trend correlated loosely with the chemical natureof the peptide-ligand carboxy-terminal amino acid preference,with class I alleles that bind basic residues in this position beingleast affected. By analysing the spectrum of peptides bound byHLA-B2705 in the presence or absence of inhibitors, they foundthat proteasome inhibition resulted in a decrease in only a smallsubset of peptides bound to HLA-B27 — and consequently thatthe majority of peptides (with basic carboxyl termini) that normallybound to this allele could be generated by proteasome-inhibitor-resistant activities. The source of protein substrates for thisactivity was as varied as that for the proteasome and includedcytosolic, nuclear, membrane and mitochondrial proteins.

Selected by Marc BonnevilleInstitut de Biologie, Nantes, France

e-mail: bonnevil@nantes.inserm.fr

•• Epithelial secretion of C3 promotes colonization of theupper urinary tract by Escherichia coli. Springall T,Sheerin NS, Abe K, Holers VM, Wan H, Sacks S: Nat Med2001, 7:801-806.Significance: Although complement has been shown previ-ously to be involved in exacerbation of the inflammatory response

ImmunologyPaper alert

Contents (chosen by)

625 Antigen processing and recognition (Elliott)625 Innate immunity (Bonneville)626 Lymphocyte development (Kruisbeek)627 Tumour immunology (Walker)628 Lymphocyte activation and effector functions (Essayan)629 Immunity to infection (Glaichenhaus and Vyakarnam)631 Immunogenetics (Casanova)631 Immunotherapy (Liu)632 Transplantation (Auchincloss, Waneck and LeGuern)633 Allergy and hypersensitivity (Akdis)

Antigen processing and recognition

Innate immunity

associated with pyelonephritis, this is the first study documentinga direct role for complement components in renal infection.Findings: The role of complement in renal infection wasinvestigated in a model of E.-coli-induced pyelonephritis inC3- or C4-deficient mice. In vitro, renal epithelial cells internalized up to 10-fold less bacteria in the absence of C3.Complement receptor (CR)1-related protein y (Crry) was thelikely receptor for bacterial internalization since it is the only C3-binding protein present on renal epithelial cells.Accordingly, binding of opsonized bacteria was inhibited bythe soluble fusion protein Crry−Ig, which blocks the interaction between C3 bound to bacteria and C3-receptors.Moreover, upregulation of C3 production by renal epithelialcells after lipopolysaccharide stimulation enhanced bacterialinternalization. This indicates that E. coli might use locally produced C3 to invade the renal epithelium.

• Contribution of the innate immune system to autoimmunemyocarditis: a role for complement. Kaya Z, Afanasyeva M,Wang Y, Dohmen KM, Schlichting J, Tretter T, Fairweather DL,Holers VM, Rose NR: Nat Immunol 2001, 2:739-745.Significance: Complement has been shown to participate inthe effector phase of several autoimmune diseases but its con-tribution to initiation of autoimmunity has not been establishedyet. This study provides the first strong evidence for a key rolefor the complement system in the induction of an autoimmunedisease, possibly through direct activation of complement-receptor-expressing T cells.Findings: The role of complement in autoimmunity was studiedin a murine model of autoimmune myocarditis induced afterimmunization with cardiac myosin. Depletion of the C3 compo-nent during the inductive phase of disease abrogated thedevelopment of myocarditis. The prevalence and severity of thedisease were drastically reduced in CR1- and CR2-deficientmice, indicating that complement acted through these recep-tors. Moreover both CR1 and CR2 were identified on a subsetof memory T cells and shown to be involved in the induction ofB- and T-cell activation markers, T-cell proliferation and T-cellcytokine production.

• CD47 (integrin-associated protein) engagement of den-dritic cell and macrophage counterreceptors is required toprevent the clearance of donor lymphohematopoietic cells.Blazar BR, Lindberg FP, Ingulli E, Panoskaltsis-Mortari A,Oldenborg PA, Iizuka K, Yokoyama W, Taylor PA: J Exp Med2001, 194:541-549.Significance: this study describes a novel and important role ofmacrophages and DCs in the elimination of lymphohematopoi-etic cells. It also suggests that CD47, a glycoprotein broadlyexpressed on blood cells, is a key indicator of lymphohe-matopoietic cell clearance.Findings: Although CD47 has been shown to control red bloodcell clearance by macrophages through engagement of theinhibitory receptor SIRPα on the macrophages, the role ofCD47 on the clearance of other cell types has not been investigated. It is shown here that donor CD47− T and bonemarrow cells fail to engraft in immunodeficient allogeneic orcongenic CD47+ recipients, suggesting their clearance by theinnate immune system. Accordingly, dye-labelled CD47− cellswere engulfed by splenic DCs and macrophages, resulting intheir complete clearance within one day after infusion.Moreover, engraftment of CD47− cells was partly restored inhost-phagocyte-depleted recipients.

• Role of Janus kinase 3 in mast cell-mediated innateimmunity against Gram-negative bacteria. Malaviya R,Navara C, Uckun FM: Immunity 2001, 18:313-321.Significance: Mast cells play a critical role in host defenseagainst Gram− bacteria, primarily through the release of TNF-α.However, the downstream events controlling this activity remainlargely unknown. This study shows that JAK3, a protein tyrosinekinase involved in the initiation of cytokine-triggered signallingevents, is a key regulator of mast-cell-mediated immunityagainst Gram− bacteria.Findings: JAK3-deficient mice show an impaired clearance ofpathogenic E. coli, and a neutrophil influx when compared withwild-type mice. These alterations are associated with a loss ofability of JAK3-deficient mast cells to release TNF-α and areduced ability to kill phagocytozed bacteria. Consistent with akey role played by JAK3 in mast-cell responses, the neutrophilinflux, bacterial clearance and survival outcome ofmast-cell-deficient W/Wv mice were restored after reconstitu-tion with JAK3+ but not JAK3− mast cells.

Selected by Ada KruisbeekThe Netherlands Cancer Institute, Amsterdam, The Netherlands

e-mail: akru@nki.nl

•• Somatic activation of ββ-catenin bypasses pre-TCR signaling and TCR selection in thymocyte development.Gounari F, Aifantis I, Khazaie K, Hoeflinger S, Harada N,Taketo MM, Von Boehmer H: Nat Immunol 2001, 2:863-869.Significance: The Wnt/frizzled signaling cascade stimulatesT cell factor 1 (TCF-1) and lymphoid enhancer factor 1 (Lef-1)transcription factors, which have been implicated in promotingthe CD4−CD8− (DN) to CD4+CD8+ (DP) transition in thymocytedevelopment. TCF-1 and Lef-1 act as transcriptional activatorsonly when bound to the co-activator β-catenin, which is the principle effector of the Wnt pathway. The present study identifies β-catenin as a key mediator at the DN to DP transition.More importantly, it shows that β-catenin can exert its differentia-tive effects at this checkpoint in the absence of pre-TCR (or TCR) signaling. Yet, the data also suggest that Wnt signaling alonecannot provide the full range of proliferative and survival triggers.Pre-TCRs thus work in concert with Wnt/frizzled signaling at thepre-TCR-driven checkpoint.Findings: Mutant mice were created in which β-catenin wasconditionally stabilized in all thymocytes, from the CD44−

CD25+ DN3 stage onwards, This promoted development ofDP thymocytes without an αβTCR. Furthermore, activation ofβ-catenin rescued the developmental arrest in RAG-2 deficientmice. Pre-TCR signaling is therefore not required for activationof the Wnt/frizzled pathway, but differentiation induced byβ-catenin did not induce the same extent of proliferation andsurvival as that induced by the pre-TCR.

• Subversion of the T/B lineage decision in the thymus byLunatic Fringe-mediated inhibition of Notch-1. Koch U,Lacombe TA, Holland D, Bowman JL, Cohen BL, Egan SE,Guidos CJ: Immunity 2001, 15:225-236.Significance: Notch membrane-receptors regulate cell-fatedecisions in many species, and numerous studies have implicated Notch-1 signaling at various stages of T-cell development. Notch-1 also is essential for T-cell commitment in

626 Paper alert

Lymphocyte development

lymphoid progenitors (LPs), but the mechanisms involved areunknown. Increased numbers of B cells appear in the thymus ofconditional Notch-1 knockout mice, but whether this reflects achange in direction from a T-cell fate to a B-cell fate, orenhanced B-cell migration to the thymus and/or enhanced proliferation of intrathymic B-cell precursors, remains to bedefined. Using inhibition of Notch-1 function through transgenicexpression of the Notch-1 modifier Lunatic Fringe in corticalthymocytes, the present study suggests that Notch-1 activationin the thymus is required to inhibit B-cell commitment in LPsand allow these cells to choose the T-cell fate.Findings: Lunatic Fringe was ectopically expressed in corticalthymocytes through the Lck-proximal promotor. Although cortical thymocytes also express Notch-1, there was no effectof Lunatic Fringe on the thymocytes themselves. Instead,Lunatic-Fringe-transgenic thymocytes act non-autonomously toinhibit Notch-1 activation in LPs and this results in inhibition ofT-cell commitment and promotion of B-cell development in thethymus. Genetic experiments support the view that this switchin T/B-cell fate is a result of effects on Notch-1: a reduction inNotch-1 gene expression greatly enhances the ability of ectopicLunatic Fringe to induce B-cell fate; and LPs expressing constitutively active Notch-1 are refractory to the effect ofLunatic Fringe. Together, the data implicate Lunatic Fringe as acrucial regulator of Notch-1 during the T/B-lineage decision,and show that Notch-1 acts in T-cell lineage commitment byinhibiting B-cell fate.

• The earliest stages of B cell development require a chemokine stromal cell-derived factor/pre-B cellgrowth-stimulating factor. Egawa T, Kawabata K,Kawamoto H, Amada K, Okamoto R, Fujii N, Kishimoto T,Katsura Y, Nagasawa T: Immunity 2001, 15:323-334.Significance: The environmental factors essential for the earli-est stages of B-cell lymphopoiesis are poorly understood.Cytokines produced by stromal cells in the micro-environmentare important regulators of B- and T-lymphopoiesis, and one ofthese, SDF-1 (stromal cell-derived factor 1), is a chemotacticcytokine implicated in growth of B-cell precursors. Despite manystudies in mutant mice with targeted disruptions in SDF-1 andits receptor, CXCR4, it remains to be determined at which stagein their development B-cell precursors become dependent onSDF-1 and CXCR4. Egawa et al. now show that generation ofthe earliest identifiable B-cell precursor requires CXCR4.Findings: Using adult chimeric mice reconstituted with fetalliver cells from CXCR4−/− mice, it is first shown that all the veryprimitive B-cell precursor subsets are lacking in bone marrowfrom chimeras made with CXCR4−/− fetal liver. Furthermore, theauthors identify the earliest B-cell precursor in the fetal liver and show that it is dependent on SDF-1 and CXCR4 for its development, and not on IL-7. Finally, SDF-1 is shown to havemarked migratory effects on the earliest B-cell precursors, sug-gesting that it acts by regulating cell migration and cell contact.

• Stat3 in thymic epithelial cells is essential for postnatalmaintenance of thymic architecture and thymocyte survival.Sano S, Takahama Y, Sugawara T, Kosaka H, Itami S,Yoshikawa K, Miyazaki J-i, Van Ewijk W, Takeda J: Immunity2001, 15:261-273.Significance: Thymus epithelial cells (TECs) and differentiatingthymocytes mutually influence each other in a step-wise fashion, to build up the micro-environment required for cell differentiation. Although thymic architecture has been studied

for many years, little is known about the molecular signals thatorchestrate its maintenance early in life and its involution lateron. In this paper, Sano et al. identify the Stat3 protein as specifically required for maintenance of thymic architecture andthymocyte survival. Findings: Mice in which the Stat3 gene was ablated by usingthe Cre-loxP technology and the K5 promotor (directing expres-sion to stratified epithelia) have multiple abnormalities in the skinand lack Stat3 also in TECs. Thymocytes, on the other hand,exhibit normal Stat3 expression. Although primary developmentof the thymus is not affected (newborns have a normal thymus,and fetal development is normal as well), a dramatic drop in thethymus size is noted as the epithelium-specific Stat3-disruptedmice age. This is accompanied by a complete disruption of thethymic architecture (as determined by immunohistochemicalanalysis) and by a major increase in the number of apoptotic thymocytes that can be detected in situ. This is not directly dueto increased susceptibility of thymocytes to apoptotic stimuli,but to a failure of Stat−/− TECs to protect thymocytes.

•• Plasma cell differentiation requires the transcription factorXBP-1. Reimold AM, Iwakoshi NN, Manis J, Vallabhajosyula P,Szomolanyi-Tsuda E, Gravallese EM, Friend D, Grusby MJ, Alt F,Glimcher LH: Nature 2001, 412:300-307.Significance: After B lymphocytes have encountered antigens,a complex series of activation and differentiation events resultsin the generation of memory B cells and of antibody-secretingplasma cells. Multiple transcription factors that regulate theearly signaling events in activated B cells have been described,but little is known about the factors that control terminal differentiation of B cells to plasma cells. Having noticed that the expression of the ubiquitous transcription factor XBP-1 isupregulated in B lymphocytes upon activation in vitro, and isextremely high in plasma cell infiltrates in vivo, Reimold et al. investigate the role of XBP-1 in plasma cell differentiation.Findings: Using the RAG-2 complementation system,XBP-1-deficient lymphocytes could be analyzed. The numbersof T and B cells of such mice are normal, as is the spectrum ofactivation markers and proliferative potential induced in vitro inXBP-1-deficient B cells. Baseline serum immunoglobulin levelsare severely reduced in chimeric XBP-1/RAG-2-deficient mice,however, and B cells from such mice are unable to produceantibodies upon in vitro stimulation. These defects result fromlack of XBP-1, since re-expression of XBP-1 (through retroviraltransduction) restores the ability to secrete antibodies. Finally,the authors looked at the in vivo ability of B cells in chimericmice to secrete antibodies after exposure to polyoma virus orvarious model antigens. Activation of B cells and germinal cen-ter formation are normal, but antibody production of any isotypefailed to occur and plasma cells were markedly absent. Thus, byregulating terminal differentiation of B lymphocytes to plasmacells, XBP-1 controls the final step in B-cell differentiation.

Selected by Paul R WalkerUniversity Hospital Geneva, Geneva, Switzerland

e-mail: Paul.Walker@hcuge.ch

• Elucidating the autoimmune and antitumor effectormechanisms of a treatment based on cytotoxic T lympho-cyte antigen-4 blockade in combination with a B16

Paper alert 627

Tumour immunology

melanoma vaccine. Comparison of prophylaxis and therapy. van Elsas A, Sutmuller RP, Hurwitz AA, Ziskin J,Villasenor J, Medema JP, Overwijk WW, Restifo NP, Melief CJ,Offringa R et al.: J Exp Med 2001, 194:481-490.Significance: The cellular requirements and effector mechanisms for antitumour immune responses are known todiffer according to the vaccine used and the tumour modelemployed. Mechanisms of particular relevance for human cancer are those that operate in a therapeutic setting. Thisstudy shows that such mechanisms may be strikingly differentfrom those operating in a prophylactic setting and may includean autoimmune component.Findings: van Elsas et al. explored combination treatment ofB16 melanoma; treatment consisted of vaccination withgranulocyte/macrophage-colony-stimulating factor (GM-CSF)-transduced B16 tumour cells together with CTLA-4 blockade. Ina prophylactic setting, there was no absolute requirement forany individual lymphocyte subset. Indeed, complete protection inthe absence of autoimmunity could be achieved after depletionof CD8+ T cells. In contrast, the requirements for therapy of anestablished tumour were more stringent: CD8+ T cells wereessential and tumour eradication was associated with vitiligo.

• Spontaneous cytotoxic T-cell responses against survivin-derived MHC class I-restricted T-cell epitopes in situ as wellas ex vivo in cancer patients. Andersen MH, Pedersen LO,Capeller B, Brocker EB, Becker JC, thor Straten P: Cancer Res2001, 61:5964-5968.Significance: An ideal tumour antigen for immunotherapy will beexpressed in a stable manner and at a high level in a wide rangeof tumours, but not in normal cells, and it will not have tolerisedpatients’ T cells. Andersen et al. suggest that the human inhibitorof apoptosis, survivin, may fulfil these conditions.Findings: Fluorescent, multimerised HLA-A2 complexes wereconstructed using previously defined peptide epitopes derivedfrom survivin. These multimers were used to identify naturallysensitised survivin-reactive cytotoxic T lymphocytes (CTLs) in the tumour and sentinel lymph node of a melanoma patientand in a breast cancer lesion. Furthermore, these cells were cytotoxic after in vitro re-stimulation: cells that bound HLA-A2–peptide multimers were isolated from a melanoma-infiltratedlymph node and killed survivin+ melanoma and breast-cancercell lines in an HLA-A2-restricted manner. Analysis of IFN-γ-secreting, survivin-specific T cells in the blood of HLA-A2+

cancer patients showed that 6 out of 10 breast cancer patients,7 out of 14 melanoma patients and 7 out of 7 leukemia patientshad detectactable responses, whereas no responses weredetected in 20 normal HLA-A2+ donors.

• Discrepancy between ELISPOT IFN-γγ secretion and binding of A2/peptide multimers to TCR reveals interclonaldissociation of CTL effector function from TCR-peptide/MHC complexes half-life. Rubio-Godoy V, Dutoit V,Rimoldi D, Lienard D, Lejeune F, Speiser D, Guillaume P,Cerottini JC, Romero P, Valmori D: Proc Natl Acad Sci USA2001, 98:10302-10307.Significance: It is generally considered that functional tests(e.g. cytokine secretion and cytotoxicity) detect fewer peptide-specific CD8+ T cells than flow-cytometric analysis withfluorescent MHC−peptide multimers. This study demonstratesthat the reverse is sometimes the case and thus highlights thefact that a single readout of specific antitumour responses canbe misleading. On a more theoretical note, the tools used here

allow a refinement of models addressing the consequences ofTCR ligation.Findings: A T-cell line derived from lymphocytes infiltrating ahuman melanoma was composed of clones specific for various tumour antigens, as detected by IFN-γ release andMHC–peptide-multimer binding. However, one clone (LAU156/34) was apparently specific for tyrosinase368−376 on thebasis of IFN-γ release and cytotoxicity, but was unreactive withMHC–tyrosinase368−376 multimers. Nevertheless, reactivitycould be detected to MHC–tyrosinase368−376 multimers undercertain staining conditions, or with multimers synthesised withan alternative tyrosinase368−376 peptide modified at position370 (a peptide detected in melanoma cell eluates). These dataand kinetic analyses of MHC–peptide-multimer dissociation ledthe authors to conclude that there could be significant variations in the stability of TCR interaction with MHC–peptidethat could still lead to full biological function.

• Immune and clinical responses in patients with metastaticmelanoma to CD34+ progenitor-derived dendritic cell vaccine. Banchereau J, Palucka AK, Dhodapkar M,Burkeholder S, Taquet N, Rolland A, Taquet S, Coquery S,Wittkowski KM, Bhardwaj N et al.: Cancer Res 2001,61:6451-6458.Significance: The many different protocols that are used for thepreparation of DCs as immunological adjuvants make compar-isons of their in vivo efficacy difficult, particularly if the studies arenot comprehensively analysed and well controlled. Here, for thefirst time in advanced cancer patients, antigen-pulsed DCs containing a subpopulation similar to epidermal Langerhans cellsare thoroughly tested for their immunological and clinical effects.Findings: CD34+ progenitors were isolated from advanced-melanoma patients and cultured with GM-CSF,TNF-α and Flt3 ligand to produce DC-enriched cell popula-tions. These were pulsed with four melanoma-antigen-derived peptides as well as with control peptides from KLH andinfluenza antigens and used for patient immunisation (fourtimes, subcutaneously). Immune responses were assessed byIFN-γ ELISPOT and proliferation tests on peripheral-bloodT cells and by DTH tests. The immunocompetence of thepatients and the efficacy of the DC vaccine were establishedby positive responses to the control antigens in 16 out of 18patients. Furthermore, immune responses to at least onemelanoma antigen were seen in a similar proportion ofpatients. Clinical results indicated 10 out of 17 patients without disease progression (assessed 10 weeks after trialentry), with a correlation of immune response and clinical outcome. These results should encourage further controlledtrials to determine whether this DC protocol and pulsing withseveral antigens are critical for optimal clinical efficacy.

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

e-mail: essayan@cber.fda.gov

• Enforced expression of GATA-3 during T cell developmentinhibits maturation of CD8 single-positive cells andinduced thymic lymphoma in transgenic mice. Nawijn MC,Ferreira R, Dingjan GM, Kahre O, Drabek D, Karis A,Grosveld F, Hendriks RW: J Immunol 2001, 167:715-723.

628 Paper alert

Lymphocyte activation and effector functions

• Enforced expression of GATA-3 in transgenic mice inhibitsTh1 differentiation and induces the formation of aT1/ST2-expressing Th2-committed T cell compartmentin vivo. Nawijn MC, Dingjan GM, Ferreira R, Lambrecht BN,Karis A, Grosveld F, Savelkoul H, Hendriks RW: J Immunol2001, 167:724-732.Significance: A role for GATA-3 beyond Th2 regulation.Findings: Native GATA-3 expression correlated with CD69expression (maturation of dual-positive cells) on thymocytesand remained high in cells committed to CD4+ lineage, butdropped markedly in cells committed to the CD8+ lineage.Overexpression of GATA-3 under the control of the CD2 LCRwas associated with enhanced expression of TCRαβ duringpositive selection, reduced numbers of peripheral CD8+ cells,impaired thymic maturation of CD8+ cells and the developmentof thymic lymphomas (CD4+CD8+/low) with Th2 characteristics.Overexpression of GATA-3 was also associated with increasedproportions of antigen-experienced CD4+ and CD8+ T cells inthe periphery, increased proportions of peripheral T1/ST2+ Th2cells, defective Th1 differentiation, increased IgE:IgG2a ratiosand defective KLH-induced DTH response.

• Failure to induce neonatal tolerance in mice that lack bothIL-4 and IL-13 but not in those that lack IL-4 alone. Inoue Y,Konieczny BT, Wagener ME, McKenzie ANJ, Lakkis FG:J Immunol 2001, 167:1125-1128.Significance: Induction of neonatal tolerance is co-dependenton IL-4 and IL-13.Findings: Neonatal tolerance to the H-Y male antigen could beinduced in both wild-type and IL-4−/− female mice as demon-strated by acceptance of serial syngeneic skin grafts and lackof anti-H-Y cytotoxic T lymphocyte (CTL) response, but preser-vation of both analogous third-party responses. Induction ofneonatal tolerance by these criteria could not be induced inIL-4−/−IL-13−/− mice. The IL-4−/−IL-13−/− mice also demon-strated a failure to suppress antigen-driven IFN-γ production.

• Homeostatic regulation of the immune system by receptor tyrosine kinases of the Tyro 3 family. Lu Q,Lemke G: Science 2001, 293:306-311.Significance: A new family of receptor tyrosine kinases thatregulate lymphocyte survival.Findings: Mice deficient in all three Tyro 3 family receptors(Tyro 3, Axl and Mer) displayed progressive lymphadenopathyand splenomegaly associated with constitutive T- and B-cellactivation and hyperproliferation. Lymphocytic infiltration intomultiple peripheral organs was evident. All triple-mutant mice ultimately developed autoimmunity. Interestingly, Tyro 3 receptors were localized to the antigen-presenting cell (APC)compartment; adoptive transfer studies demonstrated strictAPC dependence for lymphocyte dysregulation.

• Control of CD8+ T cell activation by CD4+CD25+

immunoregulatory cells. Piccirillo CA, Shevach EM:J Immunol 2001, 167:1137-1140.Significance: The first demonstration of regulation of CD8+

T cells by these newly described immunoregulatory cells.Findings: CD4+CD25+ cells suppressed both proliferationand IFN-γ production from antigen- or mitogen-stimulatedCD8+ T cells. CD4+CD25+ cells suppressed both target-cellIL-2 production and IL-2Rα expression; using tetramers, adependence on contact among T cells was demonstrated inthe absence of APCs.

• Signaling through OX40 (CD134) breaks peripheral T-celltolerance. Bansal-Pakala P, Gebre-Hiwot Jember A, Croft M:Nat Med 2001, 7:907-912.Significance: A new and potent mechanism for reversingestablished T-cell tolerance.Findings: A single dose of an agonist antibody targetingCD134 (a member of the TNF-receptor family) was able to promote expansion and restore normal functionality in the tolerized CD4+-T-cell compartment.

• Lysophosphatidylcholine as a ligand for the immuno-regulatory receptor G2A. Kabarowski JHS, Zhu K, Le LQ,Witte ON, Xu Y: Science 2001, 293:702-705.Significance: The first report of a specific, functional receptorfor lysophosphatidylcholine (LPC) and elucidation of a potentialcross-talk pathway.Findings: LPC binds G2A (a lymphocyte-specific G-protein-coupled receptor) with high affinity, inducing dose-dependentcalcium mobilization, ERK kinase activation, and chemoattrac-tion of G2A-expressing Jurkat T cells; calcium mobilization wasinhibited both by pertussis toxin and by PMA.

• Modulation of T-cell activation by the glucocorticoid-induced leucine zipper factor via inhibition of nuclear factorκκB. Ayroldi E, Migliorati G, Bruscoli S, Marchetti C, Zollo O,Cannarile L, D’Adamio F, Riccardi C: Blood 2001, 98:743-753.Significance: A novel molecular mechanism in corticosteroid-mediated regulation of T cells.Findings: Glucocorticoid-induced leucine zipper (GILZ) isupregulated by dexamethasone and downregulated by TCRtriggering. GILZ inhibits TCR-mediated upregulation ofIL-2/IL-2R expression and NF-κB nuclear translocation, the latter through a direct protein−protein interaction.

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

e-mail: glaichenhaus@ipmc.cnrs.fr

•• Toward a defined anti-Leishmania vaccine targeting vector antigens: characterization of a protective salivaryprotein. Valenzuela JG, Belkaid Y, Garfield MK, Mendez S,Kamhawi S, Rowton ED, Sacks DL, Ribeiro JMC: J Exp Med2001, 194:331-342.Significance: Many pathogens such as Leishmania parasitesare transmitted to their vertebrate hosts by the bite of flyingarthropods. In the case of Leishmania, it was previously shownthat the saliva from the infected invertebrate vector containsproteins that enhance infection. In this study, the authors identified one of these proteins and demonstrated that it couldbe used as an efficient vaccine against Leishmania infection inmice. This is the first time that a protein from an invertebratevector has been used to protect against a pathogen transmitted by this vector. A similar strategy could possibly be used in many other diseases.Findings: The authors characterized nine salivary proteins ofPhlebotomus papatasi, the vector of L. major. As comparedwith control mice, mice vaccinated with one of these proteins,SP15, or with naked DNA coding for SP15, developed smallerlesions and exhibited lower parasite burdens upon injection ofmixtures of L. major promastigotes and salivary gland

Paper alert 629

Immunity to infection

homogenates (SGHs). Further studies demonstrated that vaccination with SP15 induced a long-lasting protective T-cellresponse and that B cells were not necessary for protection.

•• Analysis of type 2 immunity in vivo with a bicistronic IL-4reporter. Mohrs M, Shinkai K, Mohrs K, Locksley RM: Immunity2001,15:303-311.Significance: Although IL-4-secreting cells play a critical role inthe development of protective immunity to several pathogens,methods for tracking these cells in vivo have been limited. In thisstudy, the authors generated knockin mice in which IL-4-secret-ing cells also expressed the enhanced green fluorescent protein(EGFP). These mice will provide valuable reagents for assessingpathogen-specific T-cell responses in vivo.Findings: The authors have generated knockin mice in which theIL-4 gene was mutated by the introduction of an internal riboso-mal entry site (IRES) element followed by the EGFP gene and apolyadenylation signal. Upon in vitro priming under Th2 condi-tions, CD4+ T cells from these mice expressed both IL-4 andEGFP, as demonstrated by flow cytometry analysis. Infection ofthese mice with the helminth, Nippostrongylus brasiliensis,induced the appearance of EGFP+CD4+ T cells in the lymphnode and their subsequent migration to the infected tissues.Furthermore, EGFP+CD4+ T cells from infected animals conferred protection against N. brasiliensis when adoptivelytransferred to immunodeficient mice.

• Interferon-γγ-mediated site-specific clearance ofalphavirus from CNS neurons. Binder GK, Griffin DE:Science 2001, 293:303-306.Significance: Some viruses that infect neurons can be clearedfrom the central nervous system by noncytolytic mechanisms,thus avoiding permanent neurologic damage. This study wasaimed at understanding this phenomenon in the case of murineencephalomyelitis induced by infection with Sindbis virus (SV),a mosquito-borne α-virus related to equine encephalitis viruses. Findings: Although clearance of infectious SV from neurons is mainly dependent on antibodies, T cells also play a role in this process, as demonstrated by the reduced ability of antibody-knockout (µMT) mice to clear the virus. Further experiments showed that T-cell-mediated clearance of the virusdiffered between brain regions and that secretion of IFN-γ wascritical in this process.

• Concurrent naive and memory CD8+ T cell responses toan influenza A virus. Tuner SJ, Cross R, Xie W, Doherty PC:J Immunol 2001, 167:2753-2758.Significance: Earlier studies have suggested that an establishedCD8+ T cell response could suppress the clonal expansion ofnaive CD8+ T cells specific for the same or a different epitope.This study demonstrates that it is not always the case and thatmemory-T-cell responses directed to one viral epitope can actually enhance the naïve-T-cell responses directed to anotherdeterminant. Understanding the reasons for this phenomenonmay have important implications for vaccine development.Findings: Thy-1.1+CD8+ memory T cells specific for theinfluenza NP366−374 epitope were labeled with CFSE and adop-tively transferred into Thy-1.2+ B6 mice. The recipient animalswere further infected with influenza virus and T-cell responsesdirected to the influenza NP366−374 and PA224−233 determinantswere monitored by flow cytometry following staining with peptide−MHC tetramers and anti-Thy-1.1 or anti-Thy-1.2 mAbs.Although the presence of memory Thy-1.1+CD8+ T cells

specific for the NP366−374 determinant did not have any effecton the clonal expansion of naïve Thy-1.2+ NP366−374-specificT cells, Thy-1.1+CD8+ NP366−374-specific memory T cells promoted the expansion of Thy-1.2+CD8+ T cells specific forthe PA224−233 determinant.

•• Inactivation of LRG-47 and IRG-47 reveals a family ofinterferon-γγ-inducible genes with essential, pathogen-specific roles in resistance to infection. Collazo C, Yap GS,Sempowski GD, Lusby KC, Tessarollo L, Van de Woude GF,Sher A, Taylor GA: J Exp Med 2001, 194:181-187.Significance: Although the clearance of many parasites, bacteria and viruses is dependent on IFN-γ production, themechanisms by which this cytokine acts are poorly understood.Previous studies have shown that more than 200 cellular genesare induced by IFN-γ, including a family of related GTP-bindingproteins localized to the endoplasmic reticulum of the cells. Inthis study, the authors show that two of these proteins play vital,but distinct, roles in immune defense against protozoan andbacterial infection.Findings: LRG-47 and IRG-47 are two GTP-binding proteinsthat are induced by IFN-γ. The authors of this study generatedLRG-47- and IRG-47-deficient mice and tested their ability toresist infection with Listeria monocytogenes, Toxoplasma gondiiand murine cytomegalovirus (MCMV). Whereas LRG-47-deficient mice were highly susceptible to T. gondii and toL. monocytogenes, IRG-47-deficient mice were partially suscep-tible to T. gondii and completely resistant to L. monocytogenes.Furthermore, although the clearance of MCMV was previouslydemonstrated to be dependent on IFN-γ, both LRG-47- andIRG-47-deficient mice were able to clear MCMV.

• Swift development of protective effector functions innaive CD8+ T cells against malaria liver stages. Sano G,Hafalla JCR, Morrot A, Abe R, Lafaille JJ, Zavala F: J Exp Med2001, 194:173-179.Significance: Although effector CD8+ T cells play a critical rolein the elimination of several viruses and parasites, it was notclear how much time naïve CD8+ T cells require to becomeeffector cells. This study demonstrates that this differentiationprocess is more rapid than previously anticipated.Findings: The authors of this study generated TCR-transgenicmice in which most CD8+ T cells reacted to thePlasmodium yoelii circumsporozoite protein. Transgenic T cellswere labeled with CFSE, adoptively transferred into syngenicanimals and these animals were immunized or not with a recom-binant vaccinia virus expressing the circumsporozoite-proteinepitope. Mice were challenged with P. yoelii sporozoites at various time-points after immunization and the parasite loadswere measured 40 hours later. The results showed that naïveT cells require antigen priming and a differentiation period of24 hours before being able to exert in vivo antiparasitic activity.Furthermore, the development of effector functions in naïveCD8+ T cells began in the absence of detectable proliferation.

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

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

• Selective transcription and modulation of resting T cellactivity by pre-integrated HIV DNA. Wu Y, Marsh JW:Science 2001, 293:1503-1506Significance: HIV replicates efficiently in activated rather thanquiescent cells. This paper shows that the HIV gene nef can be

630 Paper alert

transcribed in quiescent CD4+ T cells prior to HIV integrationand that this pre-integration transcription of HIV nef leads to T-cell activation and virus replication. This is yet another mechanism by which HIV promotes its spread. The data haveimportant implications for HIV pathogenesis and also immunity.Findings: Resting CD4+ T cells infected with HIV producedmore IL-2 than uninfected cells following stimulation with anti-CD3/28 beads. This stimulation was not blocked by AZT (aninhibitor of HIV reverse-transcription [RT]). The addition of AZTdid not block IL-2 production by anti-CD3/28 bead stimulation.But the HIV-enhanced IL-2 response was lost in the presenceof AZT. This implies that reverse transcription, and notvirion–cellular interactions, were responsible for HIV-enhanced IL-2 secretion. Full-length HIV DNA was easilydetected in resting cells by PCR for late products of HIV RT.However, no evidence for HIV integration was noted afteramplifying the junction between the nearest Alu sequence (aubiquitous repeat element in the human genome) and the HIVLTR with a primer that detected integrated proviral DNA. Underconditions where integration was not detected, HIV-1 nef tran-scripts were amplified, as detected by RT-PCR using primersthat were based on variable regions in splicing donor andacceptor sites in the common precursor that serves as themRNA for gag/pol genes and viral genomic RNA. Infectionwith a non-integrating, non-replicating HIV strain containing amutation in viral integrase resulted in similar levels of HIV neftranscripts as the wild-type (wt) virus, confirming that HIV integration was not essential for nef transcription. By westernblot, Nef protein was also detected in resting cells. IL-2 secretion by cells infected with equivalent virion levels of wt orintegrase-mutant HIV were similar. Mutations in Nef, however,impaired HIV-enhanced IL-2 production following anti-CD3/CD28 stimulation. The ability of Nef to promote an activestate in resting cells resulted in enhanced viral replication com-pared with the Nef− virus. The capacity of preintegrationtranscription by HIV might be important in regulating the function of cells where binding and entry but not integrationcan occur. Moreover, unintegrated HIV might induce cytotoxicT lymphocytes that can potentially recognise and destroy a cellthat is not replicating virus.

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

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

• A mutation in Bruton’s tyrosine kinase as a cause of selective anti-polysacharide antibody deficiency.Wood PMD, Mayne A, Joyce H, Smith CIE, Granoff DM,Kumararatne DS: J Pediatr 2001, 139:148-151.Significance: This is the first identification of a molecular basisin a patient with selective anti-polysacharide antibody deficiency.Findings: A 25-year-old patient with a history of recurrent pneu-mococcal meningitis was investigated. No abnormalities of T cells,phagocytes or complement were found. The number of bloodB cells was low, and most B cells were CD5−CD27+. Serumimmunoglobulins, IgG subclasses, and antibody responses to arange of protein antigens were normal. Remarkably, no antibodyresponse was detected in response to Hemophilus influenzaeand Streptococcus pneumoniae polysaccharide antigens, even

after repeated vaccination with conjugated antigens. A mis-sensemutation was found in BTK (encoding Bruton’s tyrosine kinase, anessential component of the BCR signalling pathway), the disease-causing gene of Bruton’s X-linked agammaglobulinemia. Thesame mutation was previously identified in a patient with the complete form of Bruton’s agammaglobulinemia. This report notonly expands the clinical spectrum of diseases associated withBTK mutations, but also provides the first genetic aetiology forselective anti-polysaccharide-antibody deficiency.

• A family with complement factor D deficiency. Biesma DH,Hannena AJ, van Velzen-Blad H, Mulder L, van Zwieten R,Kluijt I, Roos D: J Clin Invest 2001, 108:233-240.Significance: This is the first report on a family with inheritedfactor D deficiency.Findings: A 23-year-old patient with a history of meningococcalmeningitis was investigated. There was a normal hemolytic activity of the classical complement pathway, but a barelydetectable activity of the alternative complement pathway. Thedefective alternative-pathway-dependent hemolytic activity wascomplemented in vitro by addition of purified factor D. A non-sense homozygous mutation in the gene encoding factor Dwas identified in the proband, a relative with a history of meningi-tis and three healthy relatives. Within the extended kindred, thefive homozygotes only had a defective alternative-complementpathway. All heterozygotes had detectable levels of factor D andwere healthy. Thus, factor D deficiency is a novel autosomalrecessive disorder of the alternative-complement pathway, whichshould be sought in patients with meningococcal meningitis.

• Impairment of mycobacterial but not viral immunity by agermline human STAT1 mutation. Dupuis S, Dargemont C,Fieschi C, Thomassin N, Rosenzweig S, Harris J, Holland SM,Schreiber RD, Casanova JL: Science 2001, 293:300-303.Significance: This is the first identification of a germline STATmutation in humans.Findings: Two patients with severe mycobacterial disease wereinvestigated. One is 33 years old and had disseminated infectionfollowing bacille Calmette−Guérin vaccination in infancy; anotheris a 10-year-old child with a history of Mycobacterium aviuminfection at six years of age. Common viral illnesses of childhoodhad a normal clinical course and no opportunitic viral infectionsoccurred. The same heterozygous STAT1 mutation was found inthe two patients. The mutation is null as it impairs phosphory-lation of STAT-1, resulting in impaired activation of the two tran-scriptional complexes induced by type I and type II interferons,GAF (which consists of STAT-1 dimers) and ISGF-3 (which consists of STAT-1−STAT-2−p48 trimers). However, the mutationis dominant for one cellular phenotype and recessive for another,as it impairs GAF but not ISGF-3 activation in heterozygous cellsstimulated by interferons. This ‘experiment’ of nature demon-strates that the anti-mycobacterial, but not the anti-viral, effects ofinterferons are STAT-1-dependent and mediated by GAF.

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

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

•• The natural killer T cell ligand αα-galactosylceramide prevents autoimmune diabetes in non-obese diabetic mice.

Paper alert 631

Immunogenetics

Immunotherapy

Hong S, Wilson MT, Serizawa I, Wu L, Singh N, Naidenko OV,Miura T, Haba T, Scherer DC, Wei J et al.: Nat Med 2001,7:1052-1056.Significance: This is an elegant study that reveals NKT cells asa therapeutic target for autoimmune diseases and α-galactosyl-ceramide (α-GalCer) as a therapeutic agent.Findings: Firstly, non-obese diabetic (NOD) mice havereduced number of NKT cells and correspondingly poorcytokine response to α-GalCer; however, both production ofTh2 type cytokines (IL-4 and IL-10) and the number of NKTcells can be modulated by treatment with α-GalCer in vivo.Secondly, repeated injection of α-GalCer prevents develop-ment of spontaneous diabetes in NOD mice withoutsignificantly affecting the incidence of insulitis.

• Posttraumatic therapeutic vaccination with modifiedmyelin self-antigen prevents complete paralysis whileavoiding autoimmune disease. Hauben E, Agranov E,Gothilf A, Nevo U, Cohen A, Smirnov I, Steinman L,Schwartz M: J Clin Invest 2001, 108:591-599.Significance: Building on their previous observation that adoptivetransfer of T cells promotes recovery from trauma in the spinalcord, the authors showed a remarkable strategy to use vaccina-tion with self antigen to prevent post-traumatic spinal cord injury,thus expanding the horizon of vaccination as part of therapeutics.Findings: Firstly, immunization with spinal-cord homogenate orpurified myelin basic protein accelerated recovery from traumain the spinal cord in rats. Secondly, this effect can be achievedusing non-pathogenic antigenic epitopes. Thirdly, rats that aremore resistant to the induction of experimental autoimmuneencephalomyelitis displayed better functional recovery afterspinal-cord injury.

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

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

• Role of CD4+ and CD8+ cells in allorecognition: lessonsfrom corneal transplantation. Boisgérault F, Liu Y, Anosova N,Ehrlich E, Dana MR, Benichou G: J Immunol 2001,167:1891-1899.Significance: Corneal allografts enjoy high rates of spontaneousacceptance compared with other types of transplantation. Only60% of fully allogeneic murine corneal allografts, which are naturally devoid of MHC class II+ antigen-presenting cells(APCs), are rejected, apparently through an indirect mechanism.Although CD8+ cells are activated via the direct pathway, theycannot contribute to rejection unless they receive an additionalsignal provided by professional APCs in the periphery.Findings: Using ELISPOT assays to characterize the T-cellresponse, this study showed that rejection of C57BL/6 cornealallografts by BALB/c mice is associated mainly with productionof IL-2 by CD4+ cells, and IFN-γ by CD8+ cells. Under thesame conditions, no IL-5-producing and only a few IL-4-producing cells were detected. The indirect alloresponse is notdirected toward MHC-derived peptides, but mainly againstminor H antigens. Mice that had accepted corneal allograftscould be induced to reject them by subsequent grafting of allogeneic skin, showing that the ability to recognize cornealallografts was not deficient in acceptor mice.

• Antigen-specific blockade of T cells in vivo using dimeric MHC peptide. O’Herrin SM, Slansky JE, Tang Q,Markiewicz MA, Gajewski TF, Pardoll DM, Schneck JP,Bluestone JA: J Immunol 2001, 167:2555-2560.Significance: Antigen-specific inhibition of an alloreactiveTCR-transgenic T-cell population in vivo, using dimeric MHC–Igfusion proteins, blocked the rejection of allogeneic tumor cells.The effect appears to be mediated by modulation of TCRexpression and signal transduction, rather than simple blockade.Soluble MHC dimers may therefore be a potential means ofinducing sustained antigen-specific T-cell unresponsiveness inclinical organ transplantation.Findings: Using 2C TCR-transgenic mice specific for ananomer peptide (QL9) in the context of Ld, as well as a strongagonist peptide (SIY) in the context of Kb, the addition ofnanomolar levels of dimeric MHC–peptide complexes to 2CT cells in vitro induced TCR downmodulation and inhibition ofcytolytic activity. These concentrations are well below that necessary to visualize MHC–peptide dimer binding by flowcytometry, suggesting a mechanism besides steric hinderance.CD69 expression was upregulated and phosphorylation ofCD3ζ and ZAP-70 was induced, even in the absence of cross-linking, indicative of early activation events. Simultaneousadministration of Ld-bearing tumor cells and the QL9-loaded Ld

dimer significantly inhibited rejection in an adoptive transfermodel. Surprisingly, ‘irrelevant’ MCMV-peptide-loaded Ld dimersimilarly inhibited rejection, despite lack of in vitro activity, by amechanism that is not yet understood.

• Enhancement of CD8+ T cell responses by ICOS/B7hcostimulation. Wallin JJ, Liang L, Bakardjiev A, Sha WC:J Immunol 2001, 167:132-139.Significance: The results of this study suggest that ICOS maybe an especially important co-stimulatory molecule for secondary responses by CD8+ T cells and, in this case, maypreferentially support type-one cytokine production.Findings: The authors studied the role of ICOS as a co-stimu-latory molecule for CD8+ T cells in the absence of CD4+

cells. They found three important results: firstly, B7h provided excellent co-stimulation via ICOS for CD8+ cells in the absenceof CD4+ cells; secondly, the effect was especially pronouncedfor previously sensitized cells; and, thirdly, sensitized CD8+

cells co-stimulated through ICOS produced IL-2 and IFN-γ.

• Oral exposure to alloantigen generates intragraft CD8+

regulatory cells. Zhou J, Carr RI, Liwski RS, Stadnyk AW,Lee TDG: J Immunol 2001, 167:107-113.Significance: These studies demonstrate a mechanism thatappears to regulate graft rejection at the effector stage ratherthan during sensitization. The mechanism in this case is CD8+-cell-dependent rather than CD4+-cell-dependent.Findings: The authors studied the mechanisms by which oralexposure to alloantigens prolongs allograft survival. They foundthat an active infiltrate was present in the grafts after oral antigenexposure but that CD8+ T cells purified from the graft-infiltratingcells could adoptively transfer prolonged survival.

• Major histocompatibility complex class II-positive corticalepithelium mediates the selection of CD4+25+ immuno-regulatory T cells. Bensinger SJ, Bandeira A, Jordan MS,Caton AJ, Laufer TM: J Exp Med 2001, 194:427-438.Signficance: This paper provides further information about thesite of regulatory CD4+CD25+ T cell development and the

632 Paper alert

Transplantation

mechanism involved. These cells appear to play an importantrole in peripheral tolerance induction.Findings: These studies demonstrated that regulatoryCD4+CD25+ T cells did not develop in mice lacking MHCclass II molecules but did develop when mice expressed classII molecules exclusively on cortical thymic epithelium.Furthermore, the authors found that a subset of the regulatorypopulation underwent negative selection when class II expression was present on hematopoietic cells of the thymus.

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

e-mail: akdisac@siaf.unizh.ch

• Essential role for Gab2 in the allergic response. Gu H,Saito K, Klaman LD, Shen J, Fleming T, Wang YP, Pratt JC,Lin G, Lim B, Kinet J-P, Neel BG: Nature 2001, 412:186-190.Significance: Allergic responses are initiated by degranulationof mast cells after antigen stimulation of the high-affinity IgEreceptor, FcεRI, on their surface. Signal transduction eventsthrough the IgE FcεRI are intensely investigated to find a targetfor control of mast-cell degranulation. Gu et al. have identifiedGab2 as the principal activator of phosphatidylinositol 3-kinase(PI3-K) in response to FcεRI activation. Selective inhibition ofimmediate- and delayed-type-hypersensitivity responses inGab2-deficient mice suggests that suppression of Gab2 mightbe beneficial in the treatment of allergy.Findings: Gab2-deficient mice showed significantly reducedpassive cutaneous anaphylaxis. Bone marrow mast cells fromGab2−/− mice showed decreased FcεRI-induced serotoninrelease, and TNF-α and IL-6 expression compared with wild-type mice. The level of PI3-K lipid product was reduced by 80%and inositol 3-phosphate and calcium flux were impaired inGab2−/− cells.

• Brain mast cells act as an immune gate to the hypothala-mic-pituitary-adrenal axis in dogs. Matsumoto I, Inoue Y,Shimada T, Aikawa T: J Exp Med 2001, 194:71-78.Significance: Mast cells are major effector cells in IgE-dependent immediate-hypersensitivity reactions. Interestingly,numerous mast cells are found close to corticotropin-releasing-factor+ nerves in the median eminence. The study byMatsumoto and co-workers demonstrates that intracranial mastcells may act as an allergen sensor and evoke hypothalamic-pituitary-adrenal responses.Findings: A large number of mast cells are found in ventralregion of hypothalamus. When these mast cells were passivelysensitized by IgE in dogs, a marked increase in adrenal cortisolsecretion was elicited by a subsequent antigenic challenge.Degranulation of brain mast cells evoked hypothalamic-pituitary-adrenal responses via centrally released histamine andcorticotropin-releasing factor.

• Pulmonary dendritic cells producing IL-10 mediate toler-ance induced by respiratory exposure to antigen. Akbari O,DeKruyff R, Umetsu DT: Nat Immunol 2001, 2:725-731.Significance: IL-10-producing regulatory T cells are inducedby exposure to non-replicating, otherwise harmless, antigens.

This was previously demonstrated in natural exposure to bee-stings and in continuous allergen exposure during allergenimmunotherapy. New evidence suggests that pulmonary dendritic cells (DCs) orchestrate a mucosal tolerogenicimmune response via IL-10.Findings: Pulmonary DCs from mice exposed to ovalbumin(OVA) transiently produced IL-10. These DCs were phenotypi-cally mature, expressed increased amounts of B7-1, B7-2 andCD40, and expressed intermediate amounts of MHC class II.They stimulated the development of CD4+ T regulatory 1(Tr1)-like cells, which also produced high amounts of IL-10.Adoptive transfer of pulmonary DCs from IL-10+/+, but notIL-10−/−, mice induced antigen-specific unresponsiveness inthe recipient mice. Although DCs from pulmonary lymph nodesdid not induce increased amounts of TGF-β production inT cells, DCs from mesenteric lymph nodes, which expressedelevated amounts of TGF-β, enhanced TGF-β production inCD4+ T cells. These results suggest that bronchial lymphatictissue and mesenteric lymphatic tissue have distinct DCs withregard to the capacity to induce IL-10 or TGF-β production,leading to distinct suppressive CD4+ T cell responses.

• Deletion of a coordinate regulator of type 2 cytokineexpression in mice. Mohrs M, Blankespoor CM, Wang Z-E,Loots GG, Afzal V, Hadeiba H, Shinkai K, Rubin EM,Locksley RM: Nat Immunol 2001, 2:842-847.Significance: Genes that regulate the patterning of cytokineexpression in T helper (Th)-cell subsets remain incompletelydefined. Lineage-determining transcription factors, such asGATA3 for Th2 cells and T-bet for Th1 cells, have been identified. An evolutionarily conserved, approximately 400-bp,noncoding sequence in the intergenic region between the Th2cytokine genes IL4 and IL13 was designated ‘conserved noncoding sequence 1’ (CNS-1). Mohrs et al. demonstratethat CNS-1 represents an important locus in the control of Th2 responses.Findings: CNS-1-deficient mice showed significantlydecreased T-cell IL-4, IL-5 and IL-13 expression, whereas mast-cell IL-4 expression did not change. CNS-1−/− miceshowed significantly lower baseline serum IgE levels andimpaired Th2 development in Aspergillus-fumigatus-inducedallergic airway disease and Leishmania major infection.

• Regulation of Th2 cell differentiation by mel-18, a mam-malian Polycomb group gene. Kimura M, Koseki Y, Yamashita M,Watanabe N, Shimizu C, Katsumoto T, Kitamura T, Taniguchu M,Koseki H, Nakayama T: Immunity 2001, 15:275-287.Significance: Several transacting nuclear factors that controlTh1- and Th2-cell differentiation, such as c-maf, GATA3 andT-bet, have been reported. Here Kimura et al. demonstratethat mel-18, a mammalian Polycomb group gene, controlsTh2 cell differentiation.Findings: The production of Th2 cytokines (IL-4, IL-5 andIL-13) was significantly reduced, whereas IFN-γ was modestlyenhanced, in peripheral T cells of mel-18-deficient mice.GATA3 induction was significantly reduced and Th2 cell differ-entiation was impaired in mel-18−/− mice. The defect in Th2differentiation was associated with decreased demethylation ofthe IL-4 gene. Decreased antigen-specific IgG1 and parasite-induced lung eosinophilia were observed in the mel-18-deletedmice in vivo.

Paper alert 633

Allergy and hypersensitivity