Skewed T cell receptor V{alpha} repertoire among superantigen reactive murine T cells

Reactivity of murine T cells with viral or bacterial superantigensis clearly correlated with the expression of TCR V_ßdomains. Thus, T cells responding to the minor lymphocyte stimulatorylocus (Mls-1^a) or staphylococcal enterotoxin B (SEB) expresspredominantly TCR V_ß6 or V_ß8.2 respectively.We have investigated the involvement of the other major variableelement of the TCR, the V domain, in these superantigen responses.Using a panel of anti-TCR V mAbs, It is demonstrated that theTCR V repertoire among superantigen stimulated V_ß6⁺or V_ß8.2⁺ blasts (responding to Mls-1^a or SEB respectivelyin vitro) is altered in comparison with anti-CD3 stimulatedcells expressing the same V domains. Furthermore, the TCR Vrepertoire is strongly skewed in TCR V_ß8.2 transgenicmice that have undergone extensive peripheral clonal deletionafter SEB injection. These data imply that the V domain influencessuperantigen recognition by sthe TCR.     

Transforming growth factor-{beta} inhibits IL-4 and IFN-{gamma} production by stimulated human T cells

The present study investigates the effect of transforming growthfactor (TGF-ß on the production of IL-4 and IFN- bythe leukemia T_h0 type cell line HUT78, by freshly Isolated humanT cells, and by antigen specific human T cell clones. We foundthat IL-4 and IFN-ß, but not IL-2, production by stimulatedHUT78 cells was inhibited by TGF-ß1. TGF-ß1also reduced the accumulation of IL-4 and IFN- specific mRNAin stimulated HUT78 cells. However, IL-2 and IL-7 co-stimulatedIL-4 and IFN- production, whereas IL-1, IL-3, IL-5, IL-6, IL-8,tumor necrosis factor- or granulocyte macrophage colony stimulatingfactor had no effect. Because IL-2 is an Important helper cytokinefor the production of IL-4 and IFN-, we investigated whethersignal transductlon through the IL-2 receptor is Impaired byTGF-ß1. We found that tyrosine phosphorylatlon inresponse to IL-2 In HUT78 cells was strongly inhibited by ashort prelncubatlon with TGF-ß1. Evidence for an antagonisticrole for TGF-ß1 and IL-2 comes from the finding thathigh doses of IL-2 could partially overcome TGF-ß1mediated inhibition of IL-4 and IFN- production. Similar toIts effect on HUT78 cells, TGF-ß1 also inhibited IL-4and IFN- production by freshly Isolated T cells as well as byhuman T cell clones. Taken together, our experiments show thatthe IL-2 dependent cytokines IL-4 and IFN- are both negativelycontrolled by TGF-ß under conditions where IL-2 productionIs unaffected by a mechanism which partially involves an inhibitionof IL-2/1L-2R signal transductlon. These data Identify TGF-ßand IL-2 as mutual antagonists in the regulation of IL-4 andIFN- production.     

Dendritic cells and macrophages are required for Th1 development of CD4+ T cells from {alpha}{beta} TCR transgenic mice: IL-12 substitution for macrophages to stimulate IFN-{gamma} production is IFN-{gamma}-dependent

We have examined the antigen presenting cell (APC) requirementsfor primary T cell activation and T helper (Th) cell phenotypedifferentiation using naive CD4⁺ T cells from ß TCRtransgenic mice. Purified dendritic cells were the principalcell required for induction of primary ovalbumln peptide specificT cell activation and clonal expansion. However, dendritic cellsdid not induce differentiation of T cells toward Th1 or Th2phenotype. Addition of IL-4 during primary dendritic cell stimulationsof T cells resulted in the development of a Th2 phenotype whichproduced high levels of IL-4 during secondary and tertiary stimulation.In contrast, development of Th1 cells producing high levelsof IFN- could not be induced with dendritic cells alone butrequired the addition of appropriately activated macrophages.Addition of splenic or peritoneal B cells did not induce Th1development. Activated splenic macrophages induced Th1 developmentvia a non-MHC restricted mechanism. Thus, requirements for inductionof proliferation of naive CD4⁺ T cells are distinct from thosedirecting Th1 phenotype development. IL-12 could replace therequirement for macrophages to induce Th1 development when Tcells were activated with dendritic cells. Furthermore, thisIL-12 mediated development of Th1 cells producing high levelsof IFN- was dependent on IFN-.     

A unique pattern of lymphokine synthesis is a characteristic of certain antigen-specific suppressor T cell clones

We report that the lymphokines (IFN-) and IL-10 are co-syntheslzedby previously described CD3⁺ TCRß⁺, minor antigen-specificsuppressor T cell clones. IFN- and IL-10 are known to (I) becharacteristically produced by different helper T cell types,T_h1 and T_h2 respectively, and (II) inhibit the function of thereciprocal subset of T cells: IFN- Inhibits the function ofT_h2 and IL-10 that of T_h1 cells. Although Th0 cells are alsoknown to synthesize cytoklnes of both the T_h1- and T_h2-typeT cells, the suppressor T cells described in this report aredifferent from T_h0 cells in that they produce (I) neither IL-2nor IL-4 molecules and (II) stimulation via their CD3-TCR systemseems independent of both IL-2 and IL-4, the typical autocrinemolecules for T cell proliferation. The lymphokine profile ofthese suppressor T (TJ cell clones, as well as those of humanantigen-specific T. cells reported earlier, suggests that co-synthesisof some T_h1-llke and some T_h2-like cytoklnes may be a characteristicof antigen-specific T, cells as opposed to the type of reciprocalinhibition mediated through IFN- or IL-10, which is antigennon-specific.     

Peripheral lymphoid development and function in TCR mutant mice

We describe the development and function of the peripheral lymphoidsystem of mutant mice rendered deficient in either ßor T cells via targeting of TCR genes In embryonic stem cells.In the spleen of ß T cell-deficient mice, T cellsdo not compensate in numbers for the lack of ß Tcells, but B cells do. ß T cell-deficient mice areunable to mount an antibody response to ovalbumln and do notreject skin allografts. Natural killer cell function is notimpaired in any of the mutant mice. TCR mutant mice will proveuseful in dissecting differential functions of ßand T cells in vivo.     

Human {alpha}{beta} and {gamma}{delta} T cells from unexposed individuals respond to protein antigens of the yeast form of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis, a dimorphic fungus, causes chronicgranuiomatous mycosis in susceptible individuals. Differentreports have shown that cell-mediated immunity is essentialfor protection against systemic mycosis, including paracoccldloidomycosis.We analyzed the reactivity of ß and T cells fromunexposed Caucasian donors to P. brasiliensis yeast form components.Our results indicate: (I) ß and T cells proliferateafter in vitro stimulation with lysates of P. brasiliensis;(II) similar numbers of ß T cells (f = 1/21,000) andof T cells (f = 1/8000) respond to P. braslllensls; (III) P.braslllensls-reactive T cells express the V9V2 TCR; (Iv) thestimulatory activity of P. brasilensis for both ßand T cells primarily resides in a high molecular weight (100kDa) and in a low molecular weight (<<1 kDa) fraction;(v) the ligands responsible for stimulation of both ßand T cells are sensitive to proteinase treatment We concludethat both ß and T cells from healthy individualsrespond to ubiquitous protein antigens of P. brasiliensis.     

B7 2 (CD86) is essential for the development of IL-4-producing T cells

The CD28/CTLA-4 ligands, B7–1 (CD80) and B7–2 (CD86),provide a co-stimulatory signal necessary for optimal T cellactivation. We have examined the effect of blocking B7–1and B7–2 in an in vitro system using ovalbumin-specificT cells from ß TCR-transgenic mice. This system allowedus to examine the interaction of B7 co-stimulators on physiologicantigen-presenting cells (APC) with antigen-specific T helperprecursor (T_hp) cells. We report that blocking T_hp/B7–1or B7–2 interactions in a primary response differentiallyaffects the cytokine profile observed in a secondary stimulation,even in the absence of additional anti-B7 antibody. Engagementof B7–2 in the primary stimulation was found to be essentialfor production of the T_h2 cytokine, IL-4, but not the T_h1 cytokines,IL-2 and IFN-, in a secondary stimulation. Conversely, inclusionof the anti-B7–1 mAb in cultures using highly purifiednaive T cells increased levels of IL-4 and significantly depressedlevels of IFN-, upon re-stimulation. The effect of the anti-B7–2mAb in reducing IL-4 production could be overcome by the additionof recombinant IL-4 in the primary stimulation. The effectsof the anti-B7–2 mAb appear to be due to blocking andnot cross-linking, as F(ab) fragments mimicked the intact antibody.Taken together, our data demonstrate that the interaction betweenThp and B7–2 favors the development of T_h2 cells.     

The development of dermatitis infiltrated by {gamma}{delta} T cells in IL-7 transgenic mice

Transgenic mice constitutively expressing IL-7 developed severedermatitis with erythroderma and alopecia. The skin lesionswere characterized by massive infiltration of mononuclear cells.Immunofluorescence staining showed that most of the infiltratingcells were T cells with the majority bearing the TCR otherthan the V5 moiety. Furthermore, the number of T cells hadincreased in the lymphold organs of the dermatitis animals.These findings idicate the strong relationship between the expressionof IL-7 and the development of T cells in vivo and the pathologicalinvolvement of proliferated and/or activated T cells in skindisease.     

Differential regulation of surface immunoglobulin and Lyb2 mediated B cell activation: II. cAMP dependent (prostaglandin E2) and independent (IFN-{gamma}) mechanisms of regulation of B lymphocyte activation

We have recently demonstrated that pharmacological agents thatelevated cAMP inhibited sigM but not Lyb2 mediated activationof murine B lymphocytes. In this report we show evidence fordifferential regulation of prostagiandin E₂ (PGE₂), a physiologicalagent that elevated cAMP and IFN- on sigM and Lyb2 mediatedB cell activation. PGE₂ inhibited anti-lgM but not anti-Lyb2induced DNA synthesis in a dose-dependent manner. Interestingly,rlFN- also inhibited anti-lgM but not anti-Lyb2 induced DNAsynthesis. rlFN- exerted its effects directly on B cells sincedepletion of T cells and G-10 Sephadex adherent cells did notalter effects of IFN- on anti-lgM and anti-Lyb2 induced DNAsynthesis. Pretreatment of B cells with IL-4 and/or IL-5 didnotprevent the IFN- mediated inhibition of the anti-lgM response.The inhibitory effect of IFN- was observed during early stagesof B cell activation. Thus IFN- inhibited anti-µ inducedblast transformation and subsequent progression into the G₁phase of the cell cycle. The differential effects exerted byPGE₂ and rIFN- appeared to be mediated by distinct mechanisms.ThusPGE₂ but not rIFN-, at concentrations inhibitory to the slgMresponse, induced elevation of intracellular cAMP levels. Theseresults demonstrate that physiologically relevant immunomodulatorssuch as PGE₂ and IFN- can differentially regulate murine B cellresponses mediated through the antigen receptor and Lyb2 moleculesby cAMP dependent and independent mechanisms. Relevance of thisregulation for the induction of antibody synthesis by T_h1 andT_h2 types of helper T cells is discussed.     

Age-dependent changes in the response to staphylococcal enterotoxin B

In the present study we investigated the response of old miceto staphylococcal enterotoxin B (SEB) immunization. Old micewere susceptible to lethal toxic shock, probably mediated bytumor necrosis factor-, although lethal toxic shock was notobserved in young mice. Old mice were able to produce more IL-2and IL-4 than young mice in response to in vivo immunizationwith SEB. V_ß8⁺CD4⁺ T cells of old mice expanded lessin vivo and were not deleted in response to SEB. However, inspite of the absence of clonal deletion, SEB was found to induceenergy of SEB reactive cells in old mice, as demonstrated byreduced in vitro T cell proliferation to SEB and reduced invitro IL-2 and IL-4 production.     

Differential production of IL-12 in BALB/c and DBA/2 mice controls IL-4 versus IFN-{gamma} synthesis in primed CD4 lymphocytes

The profile of cytokines produced by CD4 T cells is profoundlyinfluenced by the presence of IL-12. Here we demonstrate thatduring re-stimulation of antigen-specific immune responses invitro, antigen-primed lymph node cells from DBA/2 mice produced3- to 30-fold more IL-12 than did cells from BALB/c mice, whichare identical at the major histocompatibility locus. The straindifferences in IL-12 production were observed only in antigen-drivenresponses (and not in responses induced by bacterial products),and were dependent upon an interaction between CD4 T cells andlymph node adherent cells. In addition, differences in the quantityof IL-12 produced by DBA/2 and BALB/c antigen-presenting cells(APC) was not dependent on differential production of IFN- byT cells, since APC from DBA/2 mice still produced much greaterquantities of IL-12 than did BALB/c APC when each was culturedwith the same H-2^d-restricted T_h2 clones, in the complete absenceof IFN, or when each was cultured with primed (BALB/c x DBA/2)F₁T cells. The level of IL-12 produced in the cultures criticallyaffected cytokine production in CD4 T cells, since neutralizationof endogenous IL-12 in DBA/2 cultures, which are predisposedtowards developing T_h1 responses, reduced IFN- production andenhanced IL-4 synthesis to levels normally seen in BALB/c cultures,which are predisposed toward developing Th2 responses. We proposetherefore that differential production of antigen-driven IL-12is a mechanism by which the genetic background in DBA/2 andBALB/c mice can affect the pattern of cytokine synthesis byT cells during the development of adaptive immune responses.     

Anergy in vivo: down-regulation of antigen-specific CD4+ Th1 but not Th2 cytokine responses

Efficient immunologic tolerance, defined as antlgen-speclflcunresponslveness, can be peripherally induced by the l.v. Injectionof syngenelc splenocytes coupled with antigen using ethylenecarbodilmlde (ECDI). We have previously reported that unresponslvenessinduced via l.v. Injection of syngenelc splenocytes coupledwith intact, UV-lnactlvated Theiler's murine encephalomyelitisvirus (TMEV-SP) resulted in ‘split tolerance’. Bothvtrus-speclflc delayed-type hypersensltlvlty and lgG2a levelswere inhibited, whereas lgG1 levels were increased when comparedwith sham tolerized controls. In the present report we demonstratethat tolerance induced by l.v. Injection of TMEV-coupled splenocytesresulted in antigen-specific inhibition of T cell proliferation,as well as IL-2 and IFN- production in response to both wholeTMEV and the immunodomlnant viral epitope. Additionally, toleranceinduction resulted in abrogation of T_h1 -derived [IL-2, IFN-and LT/tumor necrosis factor-ß (TNF-ß)]cytokine mRNA expression in response to In vitro stimulationwith UV-inactlvated TMEV as determined by reverse transcrlptasepolymerase chain reaction. In contrast, expression of T_h2-derived(IL-4, IL-6 and IL-10) cytokine mRNA was not affected in tolerizedmice. Tolerance functioned directly at the level of CD4⁺ T_h1cells at both the induction and effector limbs as depletionof CD8⁺ T cells both prior to in vivo tolerizatlon or in vitroculture had no effect on inhibition of T_h1-specific responses.The mechanism of In vivo tolerance induction appeared to beanergy of CD4⁺ T_h1 cells since IL-2, IFN- and LT/TNF-ßmRNA expression as well as virus-specific prollferatlve responsescould be restored by addition of rlL-2 to In vitro culturesof tolerant, CD4⁺ T_h1 populations. These results suggest thatin vivo ‘split tolerance’ Induced by l.v. Injectionof ECDI-flxed, antigen-coupled splenocytes involves anergy ofTMEV-speclflc, CD4⁺ T_h1 lymphocytes and concomitant primingof T_h2 cells. The induction of antlgen-speclflc, in vivo anergyhas important implications in the design of therapeutic strategiesfor immunopathologic diseases mediated by T_h1 lymphocytes, especiallyT cell-mediated autoimmune disorders.     

Role of macrophages and {alpha}{beta} T lymphocytes in early interleukin 10 production during Listeria monocytogenes infection

Immunity to intracellular bacteria including Listeria monocytogenesis determined by T_h1 cells and CD8 T cells which produce interferon_h.Here we show that high levels of IL-10 are released by splenocytesfrom mice infected with L. monocytogenes. IL-10 was detectedon day 1 after infection, peaked on day 4, and subsequentlydeclined. Cell separation studies and experiments with RAG-1-deficientmice, which do not possess mature B cells or T cells, revealedthat the macrophage Is the major cellular source of early IL-10production. Elevated IL-10 production in RAG-1 mutants and TCRßmutants, but not in TCR mutants, Is consistent with an inhibitionof macrophage IL-10 release by ß T cells. High IL-10production was also seen after infection with another intracellularbacterium, Mycobacterlum bovis. Since IL-10 Inhibits T_h1 cellresponses, certain pathogens might use induction of this cytokineas an evasion mechanism from the protective Immune responseof the host. However, our findings showing high levels of IL-10production in infectious models which are dominated by T_h1 cellresponses suggest that IL-10 alone is insufficient for directingT_h0 differentiation into the T_h2 cell pathway. These findingstherefore challenge the view of IL-10 as a unique and decisivedetermlnator of the T_h2 cell pathway.     

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.     

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-.     

Molecular mechanisms underlying IFN-{gamma}-mediated tumor growth inhibition induced during tumor growth inhibition induced during tumor immunotherapy with rIL-12

The present studnt Investigates the molecular by which IFN-produced as a result of in vitroIL-12 addministration exertsits anty-tumor,rIL-12 was administered three or five times intomice bearing CDA1M fibrosarcoma, OV-HM ovarian carcinoma orMCH-1-A1 fibosarcoma. This regimen induced complete regressionof CSA1M and OV-HM tumors but only transient growth inhibitionof MCH-1-A1 tumors. The anty-tumor effects of Il-12 were associatatedwith enhanced induction of IFN-becouse these effects were abrogatedby pretreatment of hosts with anti-IFN- antibody.Exposure inin vitro of the three types of tumor cells to rIFN- resultedin moderate to potent inhibition of tumor cell growth.IFNstimulatedthe expression of mRNAs for an inducible type of NO synthasa(INOS)in CSA1M cells and indoleamine 2,3-dioxygenasa (IDO),an enzyme capable of degrading tryptophan, in OV-HM cells ,but induced only marginal levels of these mRNAs in MCH-I-ALcells. In association withiNOS gene expression, INF--stimulatedCSA1M cells produced a large amount of NO which functioned toinhibit their own growth in vitro. Although OV-HM and MCH-1-A1cells did not produce NO, they also exhibited NO susceptibility.Whereasthe tumor masses from IL-12-treated CSA1M-bearing mice inducedhigher levels of INOS (for CSA1M) or IDO and iNOS (for OV-HM)mRNAs,the MCH-1-A1 tumor mass expressed lower levels of iNOS mRNAalone.Moreover, massive infiltration of CD4⁺and CD8⁺ T cellsand Mac-1⁺ cells was seen only in the CSA1M and OV-HM tumors.Thus, these results indicate that IFN- produced after IL-12treatment induces the expression of various genes with potentialto modulate tumor cells and growth by acting directly on tumorecells or stimulating tumor-infiltrating lymphold cells and thatthe effectiveness of IL12 therapy is assoiated with the operation if these mechanisms.