IFN-{gamma} expression in CD8+ T cells regulated by IL-6 signal is involved in superantigen-mediated CD4+ T cell death

Infection with pathogens containing superantigens (Sags) canresult in massive excessive CD4⁺ T cell activation and deathin such conditions as toxic shock, food poisoning and autoimmunediseases. We here showed how enhancement of IL-6 signaling suppressesSag-mediated activated CD4⁺ T cell death. Sag-induced CD4⁺ Tcell death increased in IL-6 knockout (KO) mice, whereas itdecreased in mice characterized by enhanced IL-6–gp130–STAT3signaling. The serum concentration of IFN- was inversely correlatedwith the magnitude of IL-6 signaling, and IFN- deficiency inhibitedSag-induced activated CD4⁺ T cell death, suggesting that IL-6suppresses CD4⁺ T cell death via IFN- expression. Interestingly,depletion of activated CD8⁺ T cells inhibited Sag-mediated increasesin IFN- expression in IL-6 KO mice as well as the augmentedCD4⁺ T cell death. The results demonstrate that IL-6–gp130–STAT3signaling in activated CD8⁺ T cells contributes to Sag-inducedCD4⁺ T cell death via IFN- expression, highlighting this signalingaxis in CD8⁺ T cells as a potential therapeutic target for Sag-relatedsyndromes.     

T cell receptor-triggered activation of intraepithelial lymphocytes in vitro

Intraepithelial lymphocytes (IEL) of the mouse small intestinewere examined for their potential to respond to TCR signallingin vitro. Purified IEL subsets were activated using mAbs specificfor CD3, TCRßor TCR&. Thy-1⁺IEL, regardless ofTCR type, proliferated equally well in response to anti-TCRmAb with or without exogenous IL-2. In contrast, Thy-1^–TCR, CD8^– IEL required exogenous IL-2 for proliferation.No such requirement was observed for Thy-1^– TCR& IELproliferation. IEL proliferation in the absence of added IL-2was due to an IL-2 secretion/IL-2 receptor (IL-2R) autocrinepathway, since mAbs specific for IL-2 and IL-2R inhibited IELproliferation. Thy-1⁺ CD8ß^– CD4⁺CD8⁺ IEL wereunresponsive to TCR-induced proliferation but exhibited highlevels of cytolytic activity upon TCR-triggerlng. Thy-1^–non-cytolytic IEL were induced to express Thy-1 and cytolytlcactivity following activation in vitro. In addition, the involvementof the co-stimulatory molecule CD28 in IEL activation was tested.CD28 was weakly expressed by fresh IEL and anti-CD28 mAb hadno effect on TCR-triggered proliferation. However, anti-TCRstimulation increased CD28 expression on a subset of TCRßIEL and the addition of anti-CD28 mAb resulted in increasedIL-2 production, but not in increased proliferation. Our resultsindicate that IEL, including the purported extrathymlc CD8ß^–subset, can respond to TCR-driven signals via proliferationand/or cytolytlc activity.     

Herpesvirus saimiri immortalization of {alpha}{beta} and {gamma}{delta} human T-lineage cells derived from CD34+ intrathymic precursors in vitro

Herpesvirus saimiri (HVS), an agent that can infect many humancell types, has been shown to immortalize selectively TCR ß⁺CD3⁺T lymphocytes. Human T cell precursors defined as CD34⁺CD3^–CD4^–CD8^–were isolated from thymic samples and exposed to HVS in thepresence of either IL-2 or IL-7. Cultures lacking the viruswere non-viable by day 15. Test cultures, in contrast, showeda sustained proliferative activity lasting >5 months, allowingthe phenotypical and molecular analysis of the cellular progeny.In the presence of IL-7, TCR ß⁺ cells with three differentphenotypes (mainly CD4⁺CD8^–, but also CD4⁺CD8⁺ and CD4^–CD8⁺)were immortalized, whereas no TCR ⁺ cells were recovered. Kineticstudies showed that the expansion of immortalized TCR ß⁺cells was preceded by a gradual loss of CD34⁺ cells followedby a transient accumulation of two distinct cell subsets: firstCD1⁺CD4⁺CD3^– cells and then CD4⁺CD8⁺ thymocytes. Thisresembles early phenotypic changes occurring during normal intrathymicT cell development. In the presence of IL-2, in contrast, onlyTCR ⁺ cells were immortalized (mainly CD4^–CD8⁺, but alsoCD4^–CD8^–). The results show that HVS can be usedto read the CD3⁺ cellular outcome of T cell differentiationassays, including ⁺ CD4^–CD8⁺, ⁺CD4^–CD8^–, ß⁺CD4⁺CD8^–,ß⁺CD4^–CD8⁺ and ß⁺CD4⁺CD8⁺ T cells.A clear role for different cytokines (IL-2 for ⁺ cells, IL-7for ß⁺ cells) in early T cell commitment was alsoapparent.     

Resistance of BALB/c mice to Leishmania major infection is associated with a decrease in the precursor frequency of antigen-specific CD4+ cells secreting interleukin-4

BALB/c mice are highly susceptible to infection with the protozoanparasite Leishmania major and develop a chronic fatal disease.They can, however, be manipulated to resist disease and thishas been shown to correlate with increased expression of IFN_–mRNA and the absence of IL-4 mRNA in the draining lymph nodesand spleens of these animals. Here we show that anti-IL-4 oranti-CD4 treatment of BALB/c mice resulted in a reduction inthe size of the lesion and in the number of parasites in thedraining lymph nodes compared with untreated mice. The precursorfrequency of CD4⁺ T cells proliferating in response to Leishmaniaantigens in vitro in the treated animals was not significantlydifferent from untreated animals. Analysis of the lymphokinessecreted by the clonal progeny of these cells showed that theprecursor frequency of IL-4 secreting clones was at least 10-foldlower in animals treated with either mAb. However, there wasno reciprocal increase in the precursor frequencies of IFN_–secreting clones. Comparisons of the total number of precursorsof specific CD4⁺ cells secreting IFN_– showed that anti-CD4-treatedanimals, which are resistant to disease, had considerably fewerfor the first 6 weeks than untreated mice with chronic disease.Protection of BALB/c mice was therefore associated with a reductionin the numbers of precursors of cells secreting IL-4 withouta concomitant increase in the number of precursors of IFN_–secreting cells.     

Characterization of virus-primed CD8+ T cells with a type 1 cytokine profile

Infection with lymphocytic chorlomeningitis virus is associatedwith marked polyclonal activation of the CD8⁺ T cell subpopulation.In this report the cytokine production of virus-activated Tcells is analyzed and the producing cells subset is characterizedphenotypically. CoinciB. A. Askonasding with other parametersof cell-mediated immunity, splenic T cells appear which areable to release high amounts of IFN-, but not IL-5, IL-10 ortumor necrosis factor- upon short-term stimulation with anti-CD3in vitro. A similar profile is observed analyzing T cells takenfrom an inflammatory site. Phenotypically, the main cytokine-producingcell subset is found to be CD8⁺ cells targeted for homing toinflammatory sites (VLA-4^hiL-selectin^lo) of which 30–40%were positive by intracellular staining for IFN-. This subsetalso contains all T cells with a cytotoxic potential as measuredby redirected killing. An enhanced cytotoxic potential as wellas an increased capacity to produce IFN- is observed for atleast 2 months after infection and cell sorting analysis revealedthat this could be ascribed to a long-standing increase in thefrequency of CD8⁺Pgp-1^hi cells. Therefore, these results demonstratethat systemic virus infection may exert marked perturbationof the CD8⁺ T cell population resulting in generation of a long-livedsubset of primed cells with important effector potential.     

CD2 expression on murine intestinal intraepithelial lymphocytes is bimodal and defines proliferative capacity

The CD2 molecule is normally expressed on nearly all murinelymphocytes, and is co-stimulatory in T cell activation viathe antigen receptor (TCR). A naturally occurring T lymphocytepopulation that is bimodal for CD2 expression was found in theintestinal intraepithelial lymphocytes (IEL). TCRß⁺IEL contain CD2^– and CD2⁺ cells of approximately equalproportion, while TCR⁺ IEL are predominantly CD2^–. Theproliferative response of IEL to stimulation with an anti-CD3mAb or with PMA plus ionomycin co-segregated with CD2 expression;the CD2⁺ subset proliferated vigorously under these conditionswhile the CD2^– subset was much less responsive. The respondingCD2⁺ IEL contained both TCRß⁺ and TCR⁺ cells. However,activation of the CD2^– IEL with anti-CD3 mAb resultedin only the expansion of TCR⁺ IEL, while activation with PMAplus ionomycin did not promote expansion of either the TCRß⁺or the TCR⁺ IEL. These findings parallel observations in theautoimmune lpr mouse, where massive numbers of peripheral TCRß⁺CD4^–CD8^–T cells that lack CD2 expression are also hyporesponsive tomltogenic stimulation. The apparent energy of CD2^–TCRß⁺IEL, as well as CD2^– T cells from lpr mice, demonstratesthat the absence of CD2 on TCRß⁺ T lymphocytes co-segregateswith nonresponsiveness.     

Systemic administration of rIL-12 induces complete tumor regression and protective immunity: response is correlated with a striking reversal of suppressed IFN-{gamma} production by anti-tumor T cells

Unfractionated spleen cells taken from tumor-bearing mice 2weeks after tumor implantation contained tumor-primed T cellswhich produced cytokines including IL-2 and IFN- when culturedin vitro. With progressive tumor growth this initial lymphokine-producingcapacity decreased. Here, we investigated the ability of IL-12to (I) restore suppressed IFN- production, (II) cause tumorregression and (II) induce anti-tumor protective immunity. Additionof rIL-12 to spleen cell cultures from 4- to 10-week-old tumor-bearingmice resulted in a striking enhancement in the production ofIFN- compared with cultures of these cells in the absence ofrIL-12 or of normal spleen cells in the presence of rIL-12.Five I.p. injections of rIL-12 into mice bearing s.c. tumorsinduced complete tumor regression. This was found when rIL-12was given at early (1–2 weeks), intermediate (4–5weeks) or even late (7 weeks) stages of tumor growth. Furthermore,IL-12-treated mice which rejected the primary tumor exhibitedcomplete resistance to a rechallenge with the same tumor butdid not reject a second syngenetic tumor. Immunohistochemicalanalyses following IL-12 treatment revealed that CD4⁺ and CD8⁺T cells infiltrate the tumor. More importantly, IFN- mRNA expressionwas observed in fresh tumor masses from tumor-bearing mice receivingIL-12 treatment The importance of IFN- was further demonstratedby the observation that the systemic administration of anti-IFN-mAb prior to IL-12 treatment completely abrogated the anti-tumoreffect of IL-12. Thus, these results indicate that administrationof modest levels of rIL-12 to tumor-bearing mice results intumor regression through mechanisms involving reversal of suppressedIFN- production by anti-tumor T cells and the establishmentof a tumor-specific protective immune response.     

Differential regulation of antigen-specific IgG4 and IgE antibodies in response to recombinant filarial proteins

Having identified two recombinant filarial proteins (Ov27 andOvD5B) that induced patient peripheral blood mononuclear cellsto produce antigen-specific lgG4/lgE antibodies in vitro, weassessed the role these filarial antigens play in inducing antigen-specificisotype switching (4 and iv) in the absence of T cells. PurifiedCD19⁺ s^–/s^– B cells were cultured with either ofthese antigens in the presence of anti-CD40 mAb and human IL-4.Both antigen and polyclonal signals delivered by IL-4 (or IL-13)were necessary for the induction of specific lgG4/lgE antibodies.To assess the role played by cytokines produced by B lymphocytesin antigen-driven selection of the 4 or isotype, neutralizinganti-cytokine antibodies were used in vitro. While anti-IL-12antibodies did not alter the antigen-specific lgG4/lgE production,anti-IL-6, anti-IL-13 and anti-tumor necrosis factor- antibodiessignificantly inhibited the production of lgG4/lgE. Anti-IL-2and anti-IL-10 antibodies appeared to down-regulate antigen-specificlgG4 antibodies without affecting antigen-specific IgE antibodies.Although anti-CD21 antibodies had no effect on specific IgEantibodies, they up-regulated specific lgG4 antibodies, a findingparalleled by anti-CD23 antibodies. These data suggest thatcertain filarial antigen-specific lgG4/lgE responses can bedifferentially regulated and that certain endogenously producedmolecules from B cells—such as IL-2, IL-10, CD23 and CD21–playa significant role in the induction of specific isotypes ofantigen-specific antibodies.     

Thymic stroma is required for the development of human T cell lineages in vitro

Development of the T cell lineage is characterized by the homingof hematopoietic precursors to thymus, followed by their acquisitionof receptors for antigen. T cell receptors are ß or heterodimers associated with CD3 (TCR-CD3). Very early T cellprecursors in humans have been characterized as CD7+45+ cellswhich lack the T cell differentiation antigens CD1, CD2, CD3,CD4, and CD8. A phenotypically equivalent early thymocyte populationalso occurs in postnatal life, and we have previously shownthat interleukin 2 (IL2) promotes the development in vitro ofboth the ß and the T cells from these early thymocytes.Here we have analyzed the requirements of the induction of theIL2 pathway in early thymocytes, and their developmental potential.We show that: (I) thymic stromal cells, which are present inthymocyte suspensions, are necessary to induce the IL2 pathwayand the development of ß or T cell lineages fromearly thymocytes in vitro; and (II) when removed from the invivo environment, early thymocytes can develop in vitro intoTCR-CD3^– cells of the natural killer (NK) lineage. Weconclude that CD7+45+, CD1–2–3–4–8–early thymocytes are multipotential progenitors that, at least,have the capacity to develop into ß or T cell andNK lineages. The analysis of the mechanisms of generation andselection of human T and NK cell diversity, not feasible inbone marrow cultures, is now possible.     

Expression of the IL-2 receptor {gamma} chain on various populations in human peripheral blood

We have established two rat mAbs, TUGH4 and TUGh5, specificfor the human chain of the IL-2 receptor (IL-2R), which isknown to be shared among receptors for IL-2, IL-4 and IL-7.The antibodies bound to cell lines transfected with the human chain gene but not to their parental cell lines, and precipitated65–70 and 80–90 kDa cell surface molecules fromlysates of human T cells surface-labeled with Na¹²⁵I and chemicallycross-linked with ^[125]IL-2 respectively. Flow cytometry withTUGh4 and TUGh5 detected the chain in a wide variety of peripheralblood cell populations including CD4⁺ T cells, CD20⁺ T cells,CD20⁺ B cells, CD56⁺ natural killer cells, CD4⁺ monocytes andgranulocytes, contrasting with expression of the and ßchains of IL-2R.     

CD3{varepsilon}-mediated signals rescue the development of CD4+CD8+ thymocytes in RAG-2 / mice in the absence of TCR {beta} chain expression

Recent studies have shown that TCR ß chain expressioncan effect the differentiation of CD4^–CD8^– double-negative(DN) thymocytes to CD4⁺CD8⁺ double-positive (DP) thymocytes.The TCR ß chain is expressed on the surface of DPthymocytes in association with CD3, and chains, suggestinga potential role for CD3 components in this signaling process.We now report detection of a very tow level of surface expressionof CD3 on adult DN RAG-2^–/–; thymocytes. This surfaceCD3 was associated with CD3 and chains, as detected by anti-CD3immunoprecipitation analyses. Significantly, injection of anti-CD3mAb into RAG-2^–/– mice led to the accumulation ofan IL-2R^– CD2⁺ DP cell population and a nearly 100-foldincrease in thymic cellularity to essentially normal levels.Together, these data strongly indicate that TCR ßchain-mediated developmental signals are transduced by CD3 componentsand provide potential insights into mechanisms by which TCRß chain expression may effect this process.     

IL-4 producing CD4+ TCR{alpha} {beta}int liver lymphocytes: influence of thymus, {beta}2-microglobulin and NK1.1 expression

The present report describes developmental, phenotypic and functionalfeatures of unconventional CD4⁺ TCRß lymphocytes.In C57BL/6 mice, the majority of liver lymphocytes expressingintermediate intensity of TCRß (TCRß^int)are CD4⁺NK1.1⁺ and express a highly restricted TCR V_ßrepertoire, dominated by V_ß8 with some contributionby V^ß7 and V^ß2. Although these cells expressthe CD4 co-receptor, they are present in H2-l Aß (Aß)^+/–gene disruption mutants but are markedly reduced in ß₂-microglobulin(ß₂m)^–/– mutant mice and hence are ß₂mdependent. Thymocytes expressing the CD4⁺NK1.1⁺ TCR ßphenotype are also (ß₂m) contingent, suggesting thatthese two T lymphocyte populations are related. The CD4⁺NK1.1⁺TCRßlymphocytes in liver and thymus share several markers such asLFA-1⁺, CD44⁺, CD5⁺, LECAM-1^– and IL-2Rßa. TheCD4⁺NK1.1 ⁺ TCRß^int liver lymphocytes were not detectedin athymic nuinu mice. We conclude that ß₂m expressionis crucial for development of the CD4⁺NK1.1⁺ TCRß^intliver lymphocytes and that thymus plays a major role. CD4⁺ TCRß^intliver lymphocytes were also identified in NK1.1⁺ mouse strains,there lacking the NK1.1 marker. We assume that the NK1.1 moleculeis a characteristic marker of the CD4⁺TCR"^int liver lymphocytesin NK1.1⁺ mouse strains, although its expression is not obligatoryfor their development. The liver lymphocytes from +₂m^+/–,but not from +₂m^–/–mice are potent IL-4 producersin response to CD3 or TCRß engagement and the IL-4production by liver lymphocytes was markedly reduced by treatmentwith anti-NK1.1 mAb. We conclude that the CD4+NK1.1⁺ TCRß^intliver lymphocytes are capable of producing IL-4 in responseto TCR stimulation.     

Resident CD4+ {alpha}{beta} T cells of the murine female genital tract: a phenotypically distinct T cell lineage that rapidly proliferates in response to systemic T cell activation stimuli

A population of CD4⁺ cells has been identified in the murinefemale genital tract (FGT). Phenotypic studies of FGT CD4⁺ cellsdemonstrate that they express CD3 and that the majority of thesecells are ßTCR⁺Thy-1⁺. Most of the Thy-1⁺CD4⁺ßTCR⁺ cells resemble memory T cells based on their expressionof CD44, L-selectin and CD45RB antigens. The vast majority ofThy-1⁺CD4⁺ßTCR⁺ FGT cells are CD5⁺ and all of themare B220^–. Systemic stimuli including infection with Trypanosomabrucel brucel, injection with anti-CD3, or bacterial superantigensstaphylococcal enterotoxin A or B cause a rapid accumulationof CD4+cells in the FGT exceeding that observed for CD4⁺ cellsin spleen and lymph nodes (LN). Expansion of the FGT CD4⁺ cells,which are phenotypically distinct from the splenic and LN CD4⁺T cells, is due to local proliferation rather than an influxof cells from the circulation. The CD4⁺ population in the FGTof adult nu/nu mice is dramatically reduced, indicating itsthymic dependency. In lpr/lpr mice, FGT CD4 cells do not displaychanges characteristic of splenic or LN CD4 cells in the sameanimals. These findings demonstrate that the CD4⁺ cells of themurine FGT are thymic dependent, but that they constitute aT cell lineage that phenotypically and, probably functionally,is distinct from other peripheral CD4⁺ T cell populations.     

IL-12 administered in vivo to young and aged mice. Discrepancy between the effects on tumor growth in vivo and cytotoxic T lymphocyte generation ex vivo: dependence on IFN-{gamma}

Because IL-12 restores allogeneic cytotoxic T lymphocyte (CTL)activity by T cells of aged mice in vitro, we initially assessedwhether IL-12 could overcome age-related deficits when givento aged mice in vivo. Growth of P815 (H-2^d) was enhanced inaged compared with young BALB/c (H-2^d) mice and tumor growthwas curtailed by IL-12 in both age groups. Unexpectedly, secondaryCTL stimulated ex vivo with P815 were reduced in IL-12-treatedmice compared with controls. Primary CTL generated ex vivo acrossMHC differences in IL-12-treated BALB/c and C57BL/6 young micewere reduced by 90–99%, were dose- and time-dependent,and were associated with reduced allo-stimulated NK-like activityand [³H]thymidine incorporation. IFN- was elevated in sera andin supernatants from allo-stimulated cultures from IL-12-treatedmice, while IL-4 was reduced in such supernatants, suggestingthat, despite reduced CTL, IL-12 was associated with increasedT_h1- and reduced T_h2-type cytokine production. IL-12 also inducedsplenomegaly, primarily due to increased numbers of cells lackingmarkers of mature T, B and NK cells, or macrophages, or polymorphonuclearleukocyte morphology. IFN- mutant mice exhibited reduced splenicenlargement in response to IL-12, suggesting that the splenomegalywas due, in part, to IFN- production. However, reduced CTL generationwas not due entirely to dilution of CTL precursor cells becausespleen cellularity and size increased 3-fold while CTL activitydecreased 10- to 100-fold, and CTL generation normalized toCD8⁺ T effector cells was still significantly reduced in IL-12-treatedmice. Interestingly, purified CD4⁺ and CD8⁺ T cells from IL-12-treatednormal mice exhibited greater proliferative and cytolytic activitiesrespectively compared with controls. Thus, effector T cellsin IL-12-treated mice were not impaired, but exhibited augmentedresponsiveness, suggesting that IL-12 induced complex interactionsamong spleen cell populations and that these effects, in part,are mediated by IFN-.     

{alpha}{beta} and {gamma}{delta} T cells in the immune response to the erythrocytic stages of malaria in mice

Mice lacking T cells with ß TCR (TCR ß–/–)or TCR (TCR –/–) were infected with the erythrocyticstages of the malaria parasite, Plasmodium chabaudi chabaudi(AS). Mice without T cells could control and reduce a primaryinfection of P. chabaudi with a slight delay in the time ofclearance of the acute phase of infection and significantlyhigher recrudescent parasitaemias compared with control intactmice. TCR –/– mice had higher levels of both serumIg and malaria-specific antibodies of the isotypes IgG3 andIgG1 compared with control mice. TCRß–/–mice, despite a striking increase in NK1.1⁺ cells and the presenceof T cells, were unable to clear their infection. Althoughthe plasma of TCR ß–/– mice containedall Ig isotypes before and during a primary infection, theywere unable to produce significant levels of malaria-specificIgG antibodies, suggesting that in the absence of ßT cells T cells are not able to provide efficient help forantibody production.     

Proliferation and apoptosis of B220+ CD4 CD8 TCR{alpha}{beta}intermediate T cells in the liver of normal adult mice: implication for Ipr pathogenesis

Small numbers of T cells have been isolated from the normalmouse liver and many of these are of the CD4^–CD8^–TCRß⁺phenotype. Larger numbers of such cells are present in the liversof mice homozygous for the Ipr mutation and the liver has beenproposed to be the site of an extrathymlc T cell developmentpathway that is expanded in Ipr/lpr mice. Using a modified separationprocedure that increases the liver T cell yield, we have beenable to characterize a subset of CD4^–CD8^–TCRß^intermediateT cells that express the B220 epltope of the CD45 molecule,and resemble in this and many other ways the accumulating Tcells in Ipr lymph nodes. These cells are an actively dividingpopulation and even in healthy, unmanipulated mice a large proportionof them are undergoing apoptosis. We propose the model thatthe normal liver is a major site for T cell destruction andthat the Ipr defect results in failure of this process withleakage of B220⁺CD4^–CD8^–TCRß⁺ cells fromthe liver to peripheral lymphoid tissues, particularly lymphnodes.     

NK1.1+ T cells from IL-7-deficient mice have a normal distribution and selection but exhibit impaired cytokine production

Particular subsets of T cells expressing the NK1.1 antigen havebeen proposed to play an immune regulatory role by their fastand strong production of cytokines, in particular IL-4. We soughtto determine factors driving the functional differentiationof NK1.1⁺ T cells. Since NK1.1⁺ T cells are exquisitely sensitiveto IL-7 stimulation, we analyzed the development, selectionand IL-4 production of NK1.1⁺ T cells in IL-7 deficient mice(IL-7–/–mice). Besides a sharp reduction of allT cell subsets, NK1.1⁺ T cells develop at normal relative frequenciesin IL-7–/–;mice. They also undergo a normal selectionprocess, as revealed by the biased V_ß TCR repertoireidentical to the one in IL-7+/+ mice. However, NK1.1₊ T cellsfrom IL-7+/+ mice were found to be impaired in IL-4 and IFN-production in in vitro and in vivo models. In addition, IL-7was able to restore IL-4 production by NK1.1⁺ thymocytes fromIL-7–/– mice. Finally, IL-7 but not IL-4 was ableto maintain and increase IL-4 production by NK1.1⁺ thymocytesfrom normal mice. These data suggest that the functional maturationof NK1.1⁺ T cells requires a cytokine-driven differentiationprocess, in which IL-7 plays a major role.     

CD4+Thy1- thymocytes with a Th-type 2 cytokine response

We have identified a small subset of CD3⁺, CD4⁺, CD8^–thymocytes that do not express Thy1 (CD90). This Thy1^–subset represents 1–3.7% of the total number of thymocytesin a naive mouse. CD4⁺Thy1^– thymocytes express high levelsof CD3, intermediate to high levels of heat-stable antigen (HSA),and low levels of CD25, CD45RB, CD69, CD44 and CD62L. They producehigh titers of IL-4 and no IFN- upon stimulation in vitro, aresponse characteristic of T_h2 cells. In the thymi of mice infectedneonatally with a high dose of the retrovirus Cas-Br-E MuLV,the frequency of CD4⁺Thy1^– cells increased ~10-fold. High-dosevirus infection resulted in decreased HSA and increased CD44expression on CD4⁺Thy1^– cells relative to cells from naivemice. CD4⁺Thy1^– cells from high-dose infected mice alsosecreted IL-4 and not IFN- upon in vitro stimulation. We previouslyreported that infection of newborn mice with a high dose ofmurine retrovirus results in the induction of a non-protectiveanti-viral T_h2 T cell response; CD4⁺Thy1^– thymocytes witha T_h2-like cytokine profile may play a role in determining thecytokine bias of this anti-viral response.