Superantigen-induced anergy of V beta 8+ CD4+ T cells induces functional but non-proliferative T cells in vivo.

The response profile of staphylococcal enterotoxin B (SEB)-primed murine V beta 8+ CD4+ and V beta 8+ CD8+ T cells was analysed upon rechallenge in vitro. While in vitro responses to secondary stimulation with SEB were reduced to background levels, the in vivo reactivity after rechallenge with SEB was retained, in that SEB-primed mice succumbed to lethal T-cell shock, lymphokines [interleukin-1 (IL-1), IL-2, Il-4, IL-6, IL-10, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha)], and lymphokine-specific mRNA accumulation could be detected in V beta 8+ CD4+ and V beta 8+ CD8+ T cells. However, V beta 8+ CD4+ T cells failed to enter the cell cycle. While the phenotype of V beta 8+ CD8+ T cells was indistinguishable from that of their counterparts from naive mice, V beta 8+ CD4+ T cells exhibited in vivo an unusual phenotype as non-proliferative but functional T cells. We conclude that in vitro-defined anergy does not disclose the functional abilities of ligand-reactive V beta 8+ T cells in vivo, and that priming with superantigen (SAg) induces in vivo a differentiation of SEB-reactive V beta 8+ CD4+ T cells into a non-proliferative but functional phenotype.     

Pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 superantigen

Superantigens (SAg) are proteins of bacterial or viral origin able to activate T cells by forming a trimolecular complex with both MHC class II molecules and the T cell receptor (TCR), leading to clonal deletion of reactive T cells in the thymus. SAg interact with the TCR through the beta chain variable region (Vbeta), but the TCR alpha chain has been shown to have an influence on the T cell reactivity. We have investigated here the role of the TCR alpha chain in the modulation of T cell reactivity to Mtv-7 SAg by comparing the peripheral usage of Valpha2 in Vbeta6(+) (SAg-reactive) and Vbeta8.2(+) (SAg non-reactive) T cells, in either BALB/D2 (Mtv-7(+)) or BALB/c (Mtv-7(-)) mice. The results show, first, that pairing of Vbeta6 with certain Valpha2 family members prevents T cell deletion by Mtv-7 SAg. Second, there is a strikingly different distribution of the Valpha2 family members in CD4 and CD8 populations of Vbeta6 but not of Vbeta8.2 T cells, irrespective of the presence of Mtv-7 SAg. Third, the alpha chain may play a role in the overall stability of the TCR/SAg/MHC complex. Taken together, these results suggest that the Valpha domain contributes to the selective process by its role in the TCR reactivity to SAg/MHC class II complexes, most likely by influencing the orientation of the Vbeta domain in the TCR alphabeta heterodimer.     

Staphylococcal enterotoxin B-induced activation and concomitant resistance to cell death in CD28-deficient HLA-DQ8 transgenic mice

HLA class II molecules present superantigens more efficiently than their murine counterpart. Therefore, transgenic mice expressing HLA-DQ8 with and without CD28 were used to address the role of CD28 in staphylococcal enterotoxin B (SEB)-driven immune responses. SEB-induced in vitro proliferation of naive DQ8.CD28(-/-) splenocytes was comparable to DQ8.CD28(+/+) cells, and was several fold higher than that of C57BL/10 and BALB/c splenocytes. SEB-activated, naive DQ8.CD28(-/-) cells in vitro produced significantly less IL-2, IL-4 and IL-10 than DQ8.CD28(+/+) cells, while IFN-gamma and IL-6 production was comparable. SEB-induced in vivo expansion of CD4(+) T cells and, to a greater extent, CD8(+) T cells was compromised in DQ8.CD28(-/-) mice, indicating that SEB-induced proliferation of CD8(+) T cells is more dependent on CD28 co-stimulation. Upon re-stimulation, SEB-primed CD28(+/+) T cells failed to proliferate but were capable of producing cytokines. Conversely, CD28(-/-) T cells were capable of proliferation, but not cytokine production. SEB-primed CD28-deficient cells produced significantly less nitric oxide when compared to CD28-sufficient cells following re-stimulation with SEB. CD28(+/+) and not CD28(-/-) mice were highly susceptible to SEB-induced lethal shock characterized by significantly elevated serum IFN-gamma. Thus, (i) efficient presentation of SEB by HLA-DQ8 circumvents co-stimulation through CD28, (ii) unique CD28-derived signals are mandatory for generation of certain effector functions, and (iii) absence of CD28-derived signals confers resistance to activation-induced cell death and protects mice from SEB-induced shock.     

Staphylococcal enterotoxin B in vivo modulates both gamma interferon receptor expression and ligand-induced activation of signal transducer and activator of transcription 1 in T cells

Superantigens (SAg) are bacterial exotoxins that provoke extreme responses in the immune system; for example, the acute hyperactivation of SAg-reactive T cells that leads to toxic shock syndrome is followed within days by strong immunosuppression. The gamma interferon (IFN-gamma) response is deeply affected in both extremes. The implication of IFN-gamma in the pathophysiology of lethal shock induced in mice after a secondary challenge with the SAg staphylococcal enterotoxin B (SEB) prompted us to study the regulation of IFN-gamma secretion and the intracellular response. We demonstrate in this study that a rechallenge with SEB becomes lethal only when given inside a critical time window after SEB priming and is associated with an increase of IFN-gamma serum release 72 h after priming. However, at this time, a selective blockade of IFN-gamma/STAT1 signaling develops in spleen cells, correlating with a lack of expression of the IFN-gamma receptor beta subunit and STAT1 in the T-cell population. Selective blockade of the STAT1 signaling pathway--while simultaneously maintaining STAT3 signaling and expression--may be a protective mechanism that shortens IFN-gamma production during the Th1 effector response. This blockade may also have consequences on switching towards a suppressor phenotype with chronic exposure to the superantigen.     

In vitro and in vivo T cell oligoclonality following chronic stimulation with staphylococcal superantigens

Microbial superantigens (SAg), including SEB and TSST-1, polyclonally activate T cells belonging to specific TCR BV families. A pathogenic role for SAg in various human diseases has been suggested, but enthusiasm for this view has been tempered by the T cell oligoclonality in these disorders. To assess whether T cell oligoclonality can emerge following protracted SAg stimulation, human PBMC were stimulated with SEB, TSST-1, or anti-CD3 mAb and maintained in culture with exogenous IL-2. Oligoclonality was appreciated by day 14 among CD4(+) and CD8(+) T cells. In addition, mice transgenic for human DR2 and DQ8 were injected weekly with SEB, and splenic CD4(+) and CD8(+) T cells were analyzed for oligoclonality. In mice that received one or three such injections, little-to-no oligoclonality was detected. In contrast, considerable oligoclonality was detected in mice that received eight weekly SEB injections. Many of these T cell oligoclones were identical to "spontaneously" arising oligoclones detected in SEB-naive mice. Thus, T cell oligoclonality can emerge following chronic SAg stimulation. In hosts who have lost tolerance to self Ag, chronic exposure to SAg may preferentially promote expansion of autoreactive T cells and facilitate development of clinical disease.     

Importance of CD8(+)Vbeta8(+) T cells in IFN-gamma-mediated prevention of toxoplasmic encephalitis in genetically resistant BALB/c mice.

In our attempt to identify a major T cell population(s) that recognizes protective Toxoplasma gondii antigens and produces interferon-gamma (IFN-gamma) for prevention of toxoplasmic encephalitis (TE), we found T cell receptor Vbeta8(+) cells to be the most frequent IFN-gamma-producing population infiltrated into the brain of T. gondii-infected BALB/c mice genetically resistant to the disease. To examine the role of IFN-gamma production by this T cell population for resistance, we transferred Vbeta8(+) immune T cells purified from spleens of infected BALB/c and IFN-gamma(/) mice into infected, sulfadiazine-treated, athymic nude mice. After discontinuation of sulfadiazine treatment, control nude mice that had not received any T cells and animals that had received Vbeta8(+) T cells from IFN-gamma(/) mice all died because of reactivation of infection (TE). In contrast, animals that had received the cells from BALB/c mice survived. Thus, IFN-gamma production by Vbeta8(+) T cells plays an important role in prevention of TE in these animals. When Vbeta8(+) immune T cells were divided into CD4(+) and CD8(+) subsets, a potent protective activity was observed only in the CD8(+) subset, whereas a combination of both subsets provided greater protection than did the CD8(+)Vbeta8(+) population alone. These results indicate that the CD8(+) subset of Vbeta8(+) T cells is a major afferent limb of IFN-gamma-mediated resistance of BALB/c mice against TE, although the CD4(+) subset of the T cell population works additively or synergistically with the CD8(+)Vbeta8(+) population.     

Active suppression induced by cutaneous exposure to bacterial superantigen is prevented by interleukin-12 treatment in vivo.

Exposure to the bacterial superantigen staphylococcal enterotoxin B (SEB) leads to inhibition of several immune responses and the induction of regulatory cells. The aim of this study was to characterize these regulatory cells further and to investigate the effect of interleukin-12 (IL-12) on superantigen-induced suppression. For this purpose BALB/c mice were injected subcutaneously with low doses of SEB that did not deplete the SEB-reactive V beta T cells. Intravenous transfer of unseparated local-draining lymph node cells from these SEB-treated animals suppressed the proliferative response of mononuclear spleen cells of naive syngeneic recipients for at least 3 weeks. The regulatory cells did not produce the type 2 cytokines, interleukin-4 (IL-4) or interleukin-10 (IL-10), or increased amounts of transforming growth factor-beta (TGF-beta). Depletion of CD8+ or SEB-reactive V beta 7+ and V beta 8+ T cells, prior to transfer, abrogated the suppressive effect. Intraperitoneal injections of IL-12 into donors, prior to SEB treatment, prevented the induction of functional regulatory cells, and treatment of recipients with IL-12, prior to receipt of cells from SEB-treated donors, prevented the suppressive effect of regulatory cells that were already induced. The data indicate that exposure to minute amounts of superantigens directly induces superantigen-reactive and CD8+ regulatory T cells and that superantigen-induced suppression can be prevented and reversed by IL-12 treatment in vivo.     

Functional plasticity of the LACK-reactive Vbeta4-Valpha8 CD4(+) T cells normally producing the early IL-4 instructing Th2 cell development and susceptibility to Leishmania major in BALB / c mice

Early production of IL-4 by LACK-reactive Vbeta4-Valpha8 CD4(+) T cells instructs aberrant Th2 cell development and susceptibility to Leishmania major in BALB / c mice. This was demonstrated using Vbeta4(+)-deficient BALB / c mice as a result of chronic infection with MMTV (SIM), a mouse mammary tumor virus expressing a Vbeta4-specific superantigen. The early IL-4 response was absent in these mice which develop a Th1 response to L. major. Here, we studied the functional plasticity of LACK-reactive Vbeta4-Valpha8 CD4(+) T cells using BALB/ c mice inoculated with L. major shortly after infection with MMTV (SIM), i. e. before deletion of Vbeta4(+) cells. These mice fail to produce the early IL-4 response to L. major and instead exhibit an IFN-gamma response that occurs within LACK-reactive Vbeta4-Valpha8 CD4(+) T cells. Neutralization of IFN-gamma restores the production of IL-4 by these cells. These data suggest that the functional properties of LACK-reactive Vbeta4-Valpha8 CD4(+) T cells are not irreversibly fixed.     

Unimpaired clearance of Mycobacterium bovis BCG infection in selectively T-cell anergic TCR-V beta 8.2 transgenic mice.

The anergy induced in mice with staphylococcal enterotoxin B (SEB) has been shown to involve selective unresponsiveness in cytokine expression. While interleukin-2 (IL-2), IL-3 and IL-4 mRNA levels are substantially reduced in anergic T cells upon restimulation with SEB, mRNA for interferon-gamma (IFN-gamma) is expressed normally. On the other hand, infection with Nippostrongylus brasiliensis is known to break an established T-cell anergy. This knowledge prompted us to examine the effect of infection with an intracellular microbe, bacillus Calmett-Guérin (BCG), on the expression of anergy induced with SEB. We have demonstrated that while the SEB-induced anergy was not abrogated by BCG infection, the V beta 8.2 transgenic mice, in which almost all T cells were anergized with SEB, were capable of developing the effective acquired protective immunity, possibly through the preserved capacity to induce IFN-gamma leading to induction of nitric oxide synthase.     

In vivo administration of interleukin-2 turns on anergic self-reactive T cells and leads to autoimmune disease.

One major mechanism of self tolerance involves the deletion of T cell clones in the thymus. In athymic mice, tolerance to self antigens must be generated extrathymically. T cells with self-reactive receptors undergo either peripheral clonal deletion or become unresponsive (i.e. anergic). The unresponsive state of human and mouse T cell clones in vitro can be reversed by the addition of exogenous interleukin (IL)-2, thus transforming anergic T cells to an activated state. Here it is shown that the in vivo delivery of IL-2 to athymic BALB/c nu/nu mice abrogates the anergic state of self-reactive V beta 3+ and V beta 11+ T cells [which are normally deleted in the minor lymphocyte stimulatory (Mls)-1b-, I-E(+)-expressing euthymic counterparts]. Thus, V beta 3+ and V beta 11+ T cells from IL-2-treated nude mice proliferate in response to T cell receptor cross-linking and acquire effector functions as measured by their ability to deliver aid to B cells upon specific stimulation. This activation correlates with the development of autoimmune manifestations (DNA autoantibodies, rheumatoid factors, erythroleukopenia and minimal change nephritis) in these IL-2-treated mice.     

Effects of superantigen and lipopolysaccharide on induction of CD80 through apoptosis of human monocytes

To investigate the mechanisms underlying superantigen (SAg) stimulation, we analyzed the effect of SAg on monocyte responses with or without lipopolysaccharide (LPS). Addition of gamma interferon (IFN-gamma) to unstimulated cultures induced a marked increase in the number of CD80(+) monocytes, which was inhibited by LPS through the action of interleukin-10. However, CD80(+) monocytes began to increase before IFN-gamma production, observed after 9 h of stimulation with staphylococcal enterotoxin B (SEB). SEB selectively increased the number of apoptotic CD80(-) monocytes, whereas LPS-treated monocytes were resistant to the apoptotic action of SEB. This SEB-induced killing was abrogated by anti-CD95 monoclonal antibody (MAb) ZB4 and anti-CD95 ligand (CD95L) MAb NOK2, suggesting a CD95-based pathway of apoptosis. Furthermore, the numbers of SEB-induced CD80(+) monocytes were partially decreased by anti-CD119 (IFN-gamma receptor) MAb and by anti-CD95L (NOK2) MAb. The CD30 expression of CD27(high) T cells induced by SEB was increased by agonistic anti-CD95 (CH11) MAb. Together, our findings showed that SEB-induced monocyte apoptosis is closely associated with the enrichment of CD80(+) monocytes generated before IFN-gamma production, followed by up-regulation of CD80 by IFN-gamma, and that LPS has negative effects in both cases. These results also suggested that induction of monocyte apoptosis is an important mechanism by which SAg exerts its anti-inflammatory effects.     

Induction of unresponsiveness to the superantigen staphylococcal enterotoxin B: cyclosporin A resistant split unresponsiveness unfolds in vivo without preceding clonal expansion

The continuous presence of antigen and powerful immune responses(exhaustive cell proliferation) of llgand reactive T cells arecurrently thought to condition clonal deletion and/or inductionof unresponsiveness to endogenous or exogenous superantigens(SAg). Here we report that in vivo induction of unresponsivenessto the SAg staphylococcal enterotoxin B (SEB) can be an immediateprocess. Within hours a large portion of ligand reactive V_ß8⁺T cells becomes clonally deleted by apoptosis. In parallel,the remaining V_ß8⁺ T cells are unresponsive to SEB,yet at the same time express functional IL-2 receptors (IL-2R)and thus are highly responsive to the growth promoting effectsof IL-2. In a subsequent step refractory IL-2R⁺V_ß8⁺T cells undergo a wave of cell proliferation for 48 h, presumablydriven by IL-2. Thereafter a large proportion of V_ß8⁺T cells succumb to apoptosis, the remaining cells display thehallmarks of split unresponsiveness, i.e.they display a selectivefallure to produce IL-2 upon SEB stimulation in vitrocombinedwith a preserved capability to express functional IL-2R. Earlydeletion and Induction of unresponsiveness to SEB are cyclosporinA (CsA) resistant, while clonal expansion with subsequent celldeletion is blocked by CsA, yet the development of split unresponsivenessis not impaired by CsA. The results suggest that IL-2 drivengrowth of refractory T cells may mimic powerful immune responsesof ligand reactive V_ß8⁺ T cells. Since unresponsivenessto SEB precedes in vivo expansion, the results as such questionthe concept of ‘exhaustive cell proliferation’ asa prerequisite for induction of unresponsiveness. In additionthey suggest that unresponsiveness (tolerance) can be inducedin the presence of CsA.     

Immunosuppression during acute Trypanosoma cruzi infection: involvement of Ly6G (Gr1(+))CD11b(+ )immature myeloid suppressor cells

Trypanosoma cruzi infection is associated with a severe unresponsiveness of spleen cells (SC) to antigens and mitogens. A high production of NO by concanavalin A (Con A)-stimulated SC from infected but not from control mice was observed. Neutralization of endogenous IFN-gamma production or treatment with NO synthase (NOS) inhibitor, L-N-monomethyl-arginine, blocked Con A-induced NO production and greatly restored proliferation by SC from infected mice. This was confirmed by using IFN-gammaR(-/-) and inducible NOS (iNOS)(-/- )knockout mice, since unresponsiveness to mitogens of SC from those infected mice was much less pronounced than in control littermates. Interestingly, SC unresponsiveness was associated with a huge increase in CD11b(+) cells that express Ly-6G (Gr1)(+) and other immature myeloid markers These cells were absent in infected IFN-gammaR(-/-) spleens. Purified immature Gr1(+)CD11b(+) cells produced NO and expressed iNOS upon IFN-gamma treatment, and were able to inhibit T cell proliferation. In addition, depletion of myeloid CD11b(+ )cells abrogated NO production and restored mitogen-induced proliferation, but not IL-2 synthesis, in SC from infected mice. IL-2 production and CD25 cell surface expression by mitogen-activated T cells were greatly depressed in SC from IFN-gammaR(-/-) and iNOS(-/- )mice, confirming that Gr1(+)CD11b(+) cells were not involved in their down-regulation. In contrast, IL-5, tumor necrosis factor and IFN-gamma production, and CD69 expression by T cells were not depressed in infected SC. The results indicate the existence of an immunosuppressive mechanism during T. cruzi infection, mediated through IFN-gamma-dependent NO secretion by immature Ly-6G (Gr1)(+)CD11b(+ )myeloid cells.     

Role of CD4(+)CD25(+) T regulatory cells in IL-2-induced vascular leak

T regulatory cells (CD4(+)CD25(+)) play an important role in the regulation of the immune response. However, little is known about the ability of T regulatory cells to regulate endothelial cell (EC) damage following activation of lymphocytes with IL-2. Therefore, in the current study, we examined the role of T regulatory cells and the subsequent T(h)1/T(h)2 bias in IL-2-mediated EC injury using the well-characterized C57BL/6 (T(h)1-biased) and BALB/c (T(h)2-biased) models. Following IL-2 treatment, BALB/c mice were less susceptible to IL-2-induced vascular leak syndrome (VLS) compared with C57BL/6 mice. Splenocytes from BALB/c mice displayed less cytotoxicity against ECs compared with those from C57BL/6 mice. Interestingly, BALB/c mice had significantly higher numbers of CD4(+)CD25(+) T regulatory cells, which proliferated more profoundly following IL-2 treatment, compared with CD4(+)CD25(+) T regulatory cells from C57BL/6 mice. In addition, T regulatory cells from naive BALB/c mice were more potent suppressors of anti-CD3 mAb-stimulated proliferation of T cells than similar cells from C57BL/6 mice. Depletion of T regulatory cells in both BALB/c and C57BL/6 mice led to a significant increase in IL-2-induced VLS. Together, the results from this study suggest that CD4(+)CD25(+) T regulatory cells play an important role in the regulation of IL-2-induced EC injury.     

Interleukin-13 protects against experimental autoimmune myocarditis by regulating macrophage differentiation

We report here that interleukin (IL)-13 protects BALB/c mice from myocarditis, whether induced by peptide immunization or by viral infection. In contrast to mild disease in IL-4 knockout (KO) BALB/c mice, IL-13 KO BALB/c mice developed severe coxsackievirus B3 (CVB3)-induced autoimmune myocarditis and myocarditogenic peptide-induced experimental autoimmune myocarditis. Such severe disease was characterized by increased cardiac inflammation, increased total intracardiac CD45(+) leukocytes, elevated anti-cardiac myosin autoantibodies, and increased cardiac fibrosis. Echocardiography revealed that IL-13 KO mice developed severe dilated cardiomyopathy with impaired cardiac function and heart failure. Hearts of IL-13 KO mice had increased levels of the proinflammatory and profibrotic cytokines IL-1beta, IL-18, interferon-gamma, transforming growth factor-beta1, and IL-4 as well as histamine. The hallmark of the disease in IL-13 KO mice was the up-regulation of T-cell responses. CD4(+) T cells were increased in IL-13 KO hearts both proportionally and in absolute number. Splenic T cells from IL-13 KO mice were highly activated, and myosin stimulation additionally increased T-cell proliferation. CD4(+)CD25(+)Foxp3(+) regulatory T-cell numbers were decreased in the spleens of IL-13 KO mice. IL-13 deficiency led to decreased levels of alternatively activated CD206(+) and CD204(+) macrophages and increased levels of classically activated macrophages. IL-13 KO mice had increased caspase-1 activation, leading to increased production of both IL-1beta and IL-18. Therefore, IL-13 protects against myocarditis by modulating monocyte/macrophage populations and by regulating their function.     

<Emphasis Type="Italic">Taenia crassiceps</Emphasis> cysticercosis: immune response in susceptible and resistant BALB/c mouse substrains

Taenia crassiceps can naturally and experimentally infect rodents in which they reproduce by budding. Differences in the susceptibility to T. crassiceps cysticercosis were found between two BALB/c substrains: BALB/cAnN (susceptible) and BALB/cJ (resistant). In chimeric mice, resistance was transferred to susceptible mice with bone marrow cells from the resistant mice, which argues in favor of an immune mediation of the resistant phenotype. To further explore the immune response that could underlie these differences in susceptibility, the specific cellular immune response elicited by the parasite was explored in both substrains. An increased proliferative response and IL-2 levels were induced by cysticercal antigens only in splenocytes from resistant mice. A decrease in the percentage of CD4(+) (11.1%), CD8(+) (17.5%) was found in splenocytes from susceptible BALB/cAnN mice. A study of the TCRV beta repertoire revealed a significant decrease in V beta 2 in both CD4(+) and CD8(+) splenocytes only in the susceptible BALB/cAnN strain.     

AsialoGM1+CD8+ central memory-type T cells in unimmunized mice as novel immunomodulator of IFN-gamma-dependent type 1 immunity

In unimmunized specific pathogen-free mice, there are unique memory-type CD8(+) T cell populations expressing asialoGM1 (ASGM1). These cells were classified into central memory-type T cells (T(CMT)) judging from their expression profile of CD44, IL-2Rbeta, CD62L and CCR7 cell-surface molecules. Among CD44(high)CD8(+) so-called memory CD8(+) T cell population, ASGM1(+)CD44(high)CD8(+) T(CMT), but not ASGM1(-)CD44(high)CD8(+) memory T cells, produced IFN-gamma by stimulation with anti-CD3 mAb. The physiological significance of ASGM1(+)CD8(+) T(CMT) as early source of IFN-gamma was also demonstrated in vivo. Namely, intravenous injection of anti-CD3 mAb (2 microg) resulted in early activation of IFN-gamma-producing ASGM1(+)CD8(+) T(CMT) cells as well as NKT and NK cells. Unexpectedly, however, few IFN-gamma-producing CD4(+) T cells were detected until 4 h after anti-CD3 mAb administration. Thus, ASGM1(+)CD8(+) T(CMT) were demonstrated to be early IFN-gamma producer, which may be crucial for T(h)1-dependent cellular immunity. Indeed, co-culture of naive CD4(+) T cells with ASGM1(+)CD8(+) T(CMT) but not ASGM1(-)CD8(+) T cells caused a great acceleration of IFN-gamma-producing T(h)1 cells in vitro. Finally, we found that T(h)1-prone C57BL/6 mice possessed higher percentage (10%) of ASGM1(+)CD8(+) T(CMT) in CD8(+) T cells compared with that (3%) of T(h)2-prone BALB/c mice. Moreover, ASGM1(+)CD8(+) T(CMT) derived from C57BL/6 mice produced higher levels of IFN-gamma compared with those from BALB/c mice. Thus, ASGM1(+)CD8(+) T(CMT), whose differentiation in vivo is genetically controlled, appear to play a critical role in the control of type 1 immunity, which is essential for therapy of tumors and infectious diseases.     

Role and regulation of IL-12 in the in vivo response to staphylococcal enterotoxin B.

Injection of a staphylococcal superantigen (SAg) such as staphylococcal enterotoxin B (SEB) in adult mice results in cytokine production and cell proliferation which can lead to septic shock. The aim of the present work was to identify the cytokines and co-stimulatory molecules regulating the in vivo systemic release of IFN-gamma, a cytokine known to play an important role in the pathophysiology associated with bacterial infections. We demonstrate in this study that (i) in contrast to lipopolysaccharide (LPS), SEB administration induces high levels of the p70, bioactive form, of IL-12; (ii) IL-12 production in response to SEB requires both CD40-dependent signals and IFN-gamma secretion; (iii) the early systemic release of IFN-gamma (3 h post-treatment) in response to SEB is IL-12 independent, while the sustained, late response (6-9 h post-treatment) requires endogenous IL-12 production; (iv) IL-12 produced during the primary SEB response (day 0) is responsible for priming cells in vivo to high IFN-gamma production upon secondary challenge (day 2); (v) the priming effect of IL-12 is TCR unrelated, as SEB-primed animals secrete high levels of IFN-gamma in response to both staphylococcal enterotoxin A and LPS administered 48 h later. The ability of bacterial SAg to induce septic shock and to modulate the immune response to unrelated antigens may therefore be related to their unique capacity to induce systemic IL-12 production in vivo. These observations also help to explain why SEB-primed animals, known to express an anergic phenotype 48 h post-treatment (as judged by defective IL-2 production and proliferation), nevertheless display an increased capacity to secrete the inflammatory cytokine IFN-gamma.     

Impaired IL-4 production by CD8+ T cells in NOD mice is related to a defect of c-Maf binding to the IL-4 promoter

CD8(+) T cells play an important role in the induction of the autoimmune response in non-obese diabetic (NOD) mice. Here we describe abnormalities in the control of cytokine production by NOD CD8(+) T cells. NOD CD8(+) T cells had an increased propensity to produce IFN-gamma upon TCR activation, in both adult and 2-week-old mice. NOD CD8(+) T cells had a reduced capacity to produce IL-4 in type 2 conditions compared to CD8(+) T cells from the diabetes-resistant strains BALB/c and C57BL/6. Both GATA-3 and c-Maf, two positive transactivators for IL-4 gene expression, were expressed in type 2 conditions at comparable levels in NOD CD8(+) T cells. The GATA-3 was functional since normal levels of IL-5 were produced and the IL-4 promoter was hyperacetylated in NOD CD8(+) T cells. In contrast, c-Maf failed to bind to its responsive element as determined by chromatin immunoprecipitation (ChIP) assay. These results suggest that NOD CD8(+) T cells possess an increased propensity to produce IFN-gamma and impaired c-Maf-dependent DNA binding activities in vivo that lead to reduced IL-4 production following TCR activation. These defects may facilitate the development of the autoimmune response by inducing an overall type 1-biased immune response in NOD mice.