TGF-beta and IL-10 regulation of IFN-gamma produced in Th2-type schistosome granulomas requires IL-12

Interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) regulate CD4+ T cell interferon-gamma (IFN-gamma) secretion in schistosome granulomas. The role of IL-12 was determined using C57BL/6 and CBA mice. C57BL/6 IL-4-/- granuloma cells were stimulated to produce IFN-gamma when cultured with IL-10 or TGF-beta neutralizing monoclonal antibody. In comparison, C57BL/6 wild-type (WT) control granuloma cells produced less IFN-gamma. IL-12, IL-18, and soluble egg antigen stimulated IFN-gamma release from C57BL/6 IL-4-/- and WT mice. IFN-gamma production in C57 IL-4-/- and WT granulomas was IL-12 dependent, because IL-12 blockade partly abrogated IFN-gamma secretion after stimulation. All granuloma cells released IL-12 (p70 and p40), and IL-12 production remained constant after anti-TGF-beta, anti-IL-10, recombinant IL-18, or antigen stimulation. C57 WT and IL-4-/- mouse granuloma cells expressed IL-12 receptor (IL-12R) beta1-subunit mRNA but little beta2 mRNA. TGF-beta or IL-10 blockade did not influence beta1 or beta2 mRNA expression. CBA mouse dispersed granuloma cells released no measurable IFN-gamma, produced IL-12 p70 and little p40, and expressed IL-12R beta2 and little beta1 mRNA. In T helper 2 (Th2) granulomas of C57BL/6 WT and IL-4-/- mice, cells produce IL-12 (for IFN-gamma production) and IL-10 and TGF-beta modulate IFN-gamma secretion via mechanisms independent of IL-12 and IL-12R mRNA regulation. We found substantial differences in control of granuloma IFN-gamma production and IL-12 circuitry in C57BL/6 and CBA mice.     

Severe CD4 T cell-mediated immunopathology in murine schistosomiasis is dependent on IL-12p40 and correlates with high levels of IL-17

C57BL/6 mice infected with the helminth Schistosoma mansoni develop small hepatic granulomas around parasite eggs, but concomitant immunization with soluble schistosome egg Ags (SEA) in CFA (SEA/CFA) causes marked exacerbation of the lesions in a Th1-dominated environment characterized by high levels of IFN-gamma. We explored the cause of the severe immunopathology by using IL-12p40(-/-) and IL-12p35(-/-) mice. SEA/CFA-immunized IL-12p40(-/-) mice, incapable of making IL-12 or IL-23, were completely resistant to high pathology, and their SEA-stimulated lymphoid cells failed to secrete significant IFN-gamma or IL-17. In contrast, SEA/CFA-immunized IL-12p35(-/-) mice, able to make IL-23 but not IL-12, developed severe lesions that correlated with high levels of IL-17, low IFN-gamma, and an expansion of activated CD4 T cells with a CD44(high)/CD62L(low) memory phenotype. In vivo administration of neutralizing anti-IL-17 mAb markedly inhibited hepatic granulomatous inflammation. Importantly, CBA mice, a naturally high pathology strain, also displayed elevated IL-17 levels comparable to those seen in the SEA/CFA-immunized BL/6 mice, and their lesions were similarly reduced by in vivo treatment with anti-IL-17. Our findings indicate that an IL-17-producing T cell population, likely driven by IL-23, significantly contributes to severe immunopathology in schistosomiasis.     

The pathogenic Th17 cell response to major schistosome egg antigen is sequentially dependent on IL-23 and IL-1β

CBA/J mice infected with the helminth Schistosoma mansoni develop severe CD4 T cell-mediated hepatic granulomatous inflammation against parasite eggs associated with a robust Th17 cell response. We investigated the requisites for Th17 cell development using novel CD4 T cells expressing a transgenic TCR specific for the major Sm-p40 egg Ag, which produce IL-17 when stimulated with live schistosome eggs. Neutralization of IL-23 or blockade of the IL-1 receptor, but not IL-6 neutralization, abrogated egg-induced IL-17 secretion by transgenic T cells, whereas exogenous IL-23 or IL-1β reconstituted their ability to produce IL-17 when stimulated by syngeneic IL-12p40-deficient dendritic cells. Kinetic analysis demonstrated that IL-17 production was initiated by IL-23 and amplified by IL-1β. Significantly, schistosome-infected IL-12p40-deficient or IL-1R antagonist-treated CBA/J mice developed markedly reduced hepatic immunopathology with a dampened egg Ag-specific IL-17 response. These results demonstrate that the IL-23-IL-1-IL-17 axis has a central role in the development of severe schistosome egg-induced immunopathology.     

V gamma 1+ T cells suppress and V gamma 4+ T cells promote susceptibility to coxsackievirus B3-induced myocarditis in mice

Coxsackievirus B3 infections of C57BL/6 mice, which express the MHC class II IA but not IE Ag, results in virus replication in the heart but minimal myocarditis. In contrast, Bl.Tg.Ealpha mice, which are C57BL/6 mice transgenically induced to express IE Ag, develop significant myocarditis upon Coxsackievirus B3 infection. Despite this difference in inflammatory damage, cardiac virus titers are similar between C57BL/6 and Bl.Tg.Ealpha mice. Removing gammadelta T cells from either strain by genetic manipulation (gammadelta knockout(ko)) changes the disease phenotype. C57BL/6 gammadelta ko mice show increased myocarditis. In contrast, Bl.Tg.Ealpha gammadelta ko mice show decreased cardiac inflammation. Flow cytometry revealed a difference in the gammadelta cell subsets in the two strains, with Vgamma1 dominating in C57BL/6 mice, and Vgamma4 predominating Bl.Tg.Ealpha mice. This suggests that these two Vgamma-defined subsets might have different functions. To test this possibility, we used mAb injection to deplete each subset. Mice depleted of Vgamma1 cells showed enhanced myocarditis, whereas those depleted of Vgamma4 cells suppressed myocarditis. Adoptively transfusing enriched Vgamma4(+) cells to the C57BL/6 and Bl.Tg. Ealpha gammadelta ko strains confirmed that the Vgamma4 subset promoted myocarditis. Th subset analysis suggests that Vgamma1(+) cells biased the CD4(+) T cells to a dominant Th2 cell response, whereas Vgamma4(+) cells biased CD4(+) T cells toward a dominant Th1 cell response.     

IL-23 is required for the development of severe egg-induced immunopathology in schistosomiasis and for lesional expression of IL-17

In infection with the trematode helminth Schistosoma mansoni, the severity of CD4 T cell-mediated hepatic granulomatous and fibrosing inflammation against parasite eggs varies considerably in humans and among mouse strains. In mice, either the natural high pathology, or high pathology induced by concomitant immunization with schistosome egg Ags (SEA) in CFA (SEA/CFA), results from a failure to contain a net proinflammatory cytokine environment. We previously demonstrated that the induction of severe immunopathology was dependent on the IL-12/IL-23 common p40 subunit, and correlated with an increase in IL-17, thus implying IL-23 in the pathogenesis. We now show that mice lacking the IL-23-specific subunit p19 are impaired in developing severe immunopathology following immunization with SEA/CFA, which is associated with a marked drop of IL-17 in the granulomas, but not in the draining mesenteric lymph nodes, and with a markedly suppressed SEA-specific IFN-gamma response regulated by a striking increase in IL-10. The granulomas are characterized by a significant reduction in Gr-1(+) cell recruitment and by alternative macrophage activation. Taken together, these results demonstrate that IL-23 per se is not necessary for the generation of IL-17-producing T cells, but is essential for the development of severe schistosome egg-induced immunopathology, and its absence cannot be overcome with other possible compensatory mechanisms.     

Exacerbated susceptibility to infection-stimulated immunopathology in CD1d-deficient mice

Mice lacking functional CD1d genes were used to study mechanisms of resistance to the protozoan parasite Toxoplasma gondii. Wild-type (WT) BALB/c mice, CD1d-deficient BALB/c mice, and WT C57BL/6 mice all survived an acute oral infection with a low dose of mildly virulent strain ME49 T. gondii cysts. In contrast, most CD1d-deficient C57BL/6 mice died within 2 wk of infection. Despite having parasite burdens that were only slightly higher than WT mice, CD1d-deficient C57BL/6 mice displayed greater weight loss and intestinal pathology. In C57BL/6 mice, CD4(+) cells can cause intestinal pathology during T. gondii infection. Compared with WT mice, infected CD1d-deficient C57BL/6 mice had higher frequencies and numbers of activated (CD44(high)) CD4(+) cells in mesenteric lymph nodes. Depletion of CD4(+) cells from CD1d-deficient mice reduced weight loss and prolonged survival, demonstrating a functional role for CD4(+) cells in their increased susceptibility to T. gondii infection. CD1d-deficient mice are deficient in Valpha14(+) T cells, a major population of NKT cells. Involvement of these cells in resistance to T. gondii was investigated using gene-targeted Jalpha18-deficient C57BL/6 mice, which are deficient in Valpha14(+) T cells. These mice did not succumb to acute infection, but experienced greater weight loss and more deaths than B6 mice during chronic infection, indicating that Valpha14(+) cells contribute to resistance to T. gondii. The data identify CD4(+) cells as a significant component of the marked susceptibility to T. gondii infection observed in CD1d-deficient C57BL/6 mice, and establish T. gondii as a valuable tool for deciphering CD1d-dependent protective mechanisms.     

Schistosoma japonicum: Infection characteristics in mice of various strains and a difference in the response to eggs

Female mice of 12 inbred strains were exposed to 20–25 cercariae of Schistosoma japonicum and infection status determined at day 40 by counting numbers of adult worms, eggs in faeces and eggs in a segment of liver. Most mouse strains appeared to be ‘permissive’ hosts although at least one strain (129/J) was shown to be relatively resistant in terms of day 40 adult worm numbers. In a radioisotopic lung assay for sensitivity to eggs, and developed as a rapid means of assessing granuloma formation, CBA/H mice were shown to differ from C57BL/6 mice in being non-responders. Histological examination of lungs of sensitized CBA/H and C57BL/6 mice injected intravenously with eggs established that granuloma formation was much more intense in C57BL/6 than CBA/H mice. Preliminary indications are that infected CBA/H mice are also low anti egg circumoval precipitin (COP) responders. Analysis of immune responses to isolated egg antigens in these two strains, and identification of the antigens of eggs to which such responses are directed in C57BL/6 mice, should provide insights into immunological disease processes (such as granulomatous inflammation) in this model system of japonicum schistosomiasis.     

IL-4 influences IL-2 production and granulomatous inflammation in murine schistosomiasis mansoni.

In previous studies the dynamics of IL-2 production by splenic cells of Schistosoma mansoni infected mice was correlated with the intensity of hepatic granulomatous inflammation. To extend those observations, the present studies examined the role of IL-4 on the immune responsiveness of infected mice. The dynamics of IL-4 production by soluble egg Ag-stimulated splenic cells was similar to that of IL-2: minimal levels at the pre-oviposition or early worm egg deposition stages (4 to 6 wk) peak production coincident with maximal granulomatous response (8 wk) followed by a concurrent decline at the chronic stage (18 to 20 wk) in both parameters. Addition of murine rIL-4 to splenocyte cultures of acutely or chronically infected mice did not significantly enhance the soluble egg Ag-elicited proliferative response. Daily injections of rIL-4 (10 to 1000 U) given for 14 days to groups of mice with acute infection, at the high dose-enhanced IL-2, but not IL-4, production. Similar treatment given to chronically infected mice did not augment diminished lymphokine production. Chronically infected mice treated with 10 to 1000 U of rIL-4 showed significantly enhanced liver granulomatous responses compared with untreated animals and the augmented granulomas contained more enlarged macrophages and connective tissue matrix. Repeated injections of anti-IL-4 mAb (11B11) given to acutely infected mice significantly suppressed splenic cell proliferation, IL-2 and IL-4 production, and hepatic granulomatous inflammation. Similar treatment given to chronically infected mice also diminished the down-modulated granulomatous response. These data demonstrate that IL-4 plays an important role in the egg-directed granulomatous response and participates in the regulation of Ag-specific lymphoproliferation, and IL-2 and IL-4 production during the course of the infection.     

Leptin modulates the survival of autoreactive CD4+ T cells through the nutrient/energy-sensing mammalian target of rapamycin signaling pathway

Chronic inflammation can associate with autoreactive immune responses, including CD4(+) T cell responses to self-Ags. In this paper, we show that the adipocyte-derived proinflammatory hormone leptin can affect the survival and proliferation of autoreactive CD4(+) T cells in experimental autoimmune encephalomyelitis, an animal model of human multiple sclerosis. We found that myelin olygodendrocyte glycoprotein peptide 35-55 (MOG(35-55))-specific CD4(+) T cells from C57BL/6J wild-type mice could not transfer experimental autoimmune encephalomyelitis into leptin-deficient ob/ob mice. Such a finding was associated with a reduced proliferation of the transferred MOG(35-55)-reactive CD4(+) T cells, which had a reduced degradation of the cyclin-dependent kinase inhibitor p27(kip1) and ERK1/2 phosphorylation. The transferred cells displayed reduced Th1/Th17 responses and reduced delayed-type hypersensitivity. Moreover, MOG(35-55)-reactive CD4(+) T cells in ob/ob mice underwent apoptosis that associated with a downmodulation of Bcl-2. Similar results were observed in transgenic AND-TCR- mice carrying a TCR specific for the pigeon cytochrome c 88-104 peptide. These molecular events reveal a reduced activity of the nutrient/energy-sensing AKT/mammalian target of rapamycin pathway, which can be restored in vivo by exogenous leptin replacement. These results may help to explain a link between chronic inflammation and autoimmune T cell reactivity.     

Beryllium skin patch testing to analyze T cell stimulation and granulomatous inflammation in the lung

Chronic beryllium disease (CBD) is characterized by granulomatous inflammation and the accumulation of CD4(+) T cells in the lung. Patch testing of CBD patients with beryllium sulfate results in granulomatous inflammation in the skin. We investigated whether the T cell clonal populations present in the lung of CBD patients would also be present in the involved skin of a positive beryllium patch test and thus mirror the granulomatous process in the lung. CBD patients with clonal TCR expansions in bronchoalveolar lavage (BAL) were selected for study. All three CBD patients studied had a positive response to beryllium sulfate application and a negative patch test to normal saline. Immunohistochemistry showed extensive infiltration with CD4(+) T cells and few, if any, CD8(+) T cells both at 3 days and at later times when granulomas were apparent. T cell infiltration early after skin testing appeared to be nonspecific with the TCR repertoire of infiltrating T cells being distinct from that present in BAL. At later times when granulomas were present, T cell clones in skin overlapped with those in BAL in all patients tested. Total TCR matches in skin and BAL were as high as 40% in selected Vbeta T cell subsets. Studies of peripheral blood T cells before and after patch testing provided evidence for mobilization of large numbers of pathogenic beryllium-reactive T cells into the circulating pool. These studies using skin patch testing provide new insight into the dynamics of T cell influx and mobilization during granulomatous inflammation.     

The effect of aging on the induction of humoral and cellular immunity and tolerance in two long-lived mouse strains.

Aging is a complex process that adversely affects most if not all components of the immune system. In this report, two long-lived mouse strains have been compared in ability to generate both antigen-specific immunity and tolerance. Although CBA/CaJ mice produced high levels of antibody following injection of aqueous preparations of aggregated human gamma-globulin (AHGG), C57BL/6 mice made only meager antibody responses to such preparations. Age dramatically affects the humoral anti-HGG response to aqueous AHGG in both strains, but the meager response of young C57BL/6 mice was at insignificant levels in aged C57BL/6 mice. Conversely, both mouse strains generated good responses following injection of HGG in complete Freund's adjuvant at both the T and B cell level as evidenced by in vitro antigen-specific T cell proliferation and anti-HGG antibody production. Aged mice of both strains showed a marked decrease in the production of serum anti-HGG antibody in comparison to young mice. Although the antigen-specific T cell proliferative response was significantly decreased in aged CBA/CaJ mice, such proliferation was not affected in aged mice of the C57BL/6 strain. Removal of CD8+ cells from lymph node T cells of either young or aged C57BL/6 mice did not increase the antigen-specific proliferative response, suggesting that loss of CD8+ suppressors during the aging process is not responsible for the high level of antigen-specific T cell proliferation in aged C57BL/6 mice. Tolerance to HGG was readily induced in both young and aged C57BL/6 and CBA/CaJ mice although aged mice demonstrate a modest resistance to tolerance induction when compared to their young counterparts. This resistance was observed in both antibody production and antigen-specific T cell proliferation.     

Analysis of egg antigens inducing hepatic lesions in schistosome infection

In schistosomiasis, granuloma formation to parasite eggs signals the beginning of a chronic and potentially life-threatening disease. Granulomas are strictly mediated by CD4⁺ T helper (Th) cells specific for egg antigens; however, the number and identity of these T cell-sensitizing molecules are largely unknown. We have used monoclonal T cell reagents as probes to track down, isolate and positively identify several egg antigens; this approach implicitly assures that the molecules of interest are T cell immunogens and, hence, potentially pathogenic. The best-studied egg component is the Sm-p40 antigen. Sm-p40 elicits a strikingly immunodominant Th-1-polarized response in C3H and CBA mice, which are characterized by severe egg-induced immunopathology. Two additional described T cell-sensitizing egg antigens are Schistosoma mansoni phosphoenolpyruvate carboxykinase (Sm-PEPCK) and thioredoxin peroxidase-1 (Sm-TPx-1). In contrast to Sm-p40, both of these molecules induce a more balanced Th-1/Th-2 response, and are relatively stronger antigens in C57BL/6 mice, which develop smaller egg granulomas. Other components, including moieties with molecular weights of 25 kDa (Sm-p25), 150/166 kDa (Sm-p155/166), and 29 kDa (Sm-GST29), are also found to stimulate specific T cells. These findings in the murine model introduce the important notion that egg antigens can vary significantly in immunogenicity according to the host's genetic background. A better knowledge of the principal immunogenic egg components is necessary to ascertain whether such responses can be manipulated for the purpose of reducing pathology.     

Goblet cell-derived resistin-like molecule beta augments CD4+ T cell production of IFN-gamma and infection-induced intestinal inflammation

The secreted goblet cell-derived protein resistin-like molecule beta (RELMbeta) has been implicated in divergent functions, including a direct effector function against parasitic helminths and a pathogenic function in promoting inflammation in models of colitis and ileitis. However, whether RELMbeta influences CD4(+) T cell responses in the intestine is unknown. Using a natural model of intestinal inflammation induced by chronic infection with gastrointestinal helminth Trichuris muris, we identify dual functions for RELMbeta in augmenting CD4(+) Th1 cell responses and promoting infection-induced intestinal inflammation. Following exposure to low-dose Trichuris, wild-type C57BL/6 mice exhibit persistent infection associated with robust IFN-gamma production and intestinal inflammation. In contrast, infected RELMbeta(-/-) mice exhibited a significantly reduced expression of parasite-specific CD4(+) T cell-derived IFN-gamma and TNF-alpha and failed to develop Trichuris-induced intestinal inflammation. In in vitro T cell differentiation assays, recombinant RELMbeta activated macrophages to express MHC class II and secrete IL-12/23p40 and enhanced their ability to mediate Ag-specific IFN-gamma expression in CD4(+) T cells. Taken together, these data suggest that goblet cell-macrophage cross-talk, mediated in part by RELMbeta, can promote adaptive CD4(+) T cell responses and chronic inflammation following intestinal helminth infection.     

Modulation of granulomatous hypersensitivity. I. Characterization of T lymphocytes involved in the adoptive suppression of granuloma formation in Schistosoma mansoni-infected mice.

The cellular basis of the spontaneous modulation of the granulomatous response to schistosome eggs was analyzed in mice infected with Schistosoma mansoni. Spleen cells of 20 or 32 week-infected mice undergoing modulation, when transferred to 6 week-infected recipients, suppressed the maximal granulomatous response at 8 weeks. Suppression of both naturally forming asynchronous liver and synchronously induced lung lesions was achieved. Specificity of this effect was demonstrated by the suppression of egg granulomas but not antigen-coated bead granulomas developing simultaneously in the lungs of cell recipients. Further characterization showed that suppression was abrogated by pretreating transferred cells with either anti-Thy 1.2 or anti-Iak alloantisera and C. Transfer of macrophage-depleted or fractionated T and B spleen cells confirmed that T cells alone transferred suppression. Moreover, an Ia antigen-bearing (Ia+) subpopulation of T cells was required in the transferred suppression. Moreover, an Ia antigen-bearing (Ia+) subpopulation of T cells was required in the transferred population. An examination of T cells obtained from isolated, dispersed lung granulomas from control and adoptively suppressed mice revealed an increased proportion of Ia+ cells in the latter. It is suggested that Ia+ T cells may be involved in the local modulation of the granulomatous response.     

Naturally occurring CD4+Foxp3+ regulatory T cells are an essential, IL-10-independent part of the immunoregulatory network in Schistosoma mansoni egg-induced inflammation

In acute and chronic schistosomiasis, survival of the host requires a carefully balanced immune response against highly immunogenic parasite eggs. We characterized the phenotype, distribution, and functional role of CD4(+)Foxp3(+) naturally occurring regulatory T cells (naTregs) in schistosome egg-induced inflammation. In adoptive transfer experiments and by intracellular staining for Foxp3, we demonstrate significant frequencies of naTregs in hepatic granulomas and draining lymphoid tissues of mice infected with the trematode Schistosoma mansoni. Strikingly, egg-induced inflammation does not change the normal ratio between naTregs and effector CD4(+) T cells at the inflammatory site or in lymphoid organs in acute or chronic disease. However, increasing frequencies of CD103-expressing cells in the naTreg compartment indicate a change in phenotype for naTregs with disease progression. Because CD103 was described recently as an activation marker for naTregs, we speculate that naTregs in chronic schistosomiasis are potentially more suppressive. Furthermore, we found that most naTregs do not contribute to egg-induced IL-4 and IL-10 production. Importantly, depletion of CD25(+) naTregs strongly enhances the frequency of IL-4-producing effector T cells in acute egg-induced inflammation. It does not change clonal expansion of activated CD4(+) T cells. This regulation of egg-induced cytokine production does not require the presence of IL-10. These data demonstrate that naTregs limit egg-induced effector-cytokine production in our model. Our results identify naTregs as an important, IL-10-independent part of the regulatory network in schistosome egg-induced inflammation.     

Role for MyD88, TLR2 and TLR9 but not TLR1, TLR4 or TLR6 in experimental autoimmune encephalomyelitis

The potential roles of TLRs in the cause and pathogenesis of autoimmune CNS inflammation remain contentious. In this study, we examined the effects of targeted deletions of TLR1, TLR2, TLR4, TLR6, TLR9, and MyD88 on the induction of myelin oligodendrocyte glycoprotein 35-55 (MOG(35-55)) peptide/CFA/pertussis toxin-induced autoimmune encephalomyelitis. Although C57BL/6.Tlr1(-/-), C57BL/6.Tlr4(-/-) and C57BL/6.Tlr6(-/-) mice showed normal susceptibility to disease, signs were alleviated in female C57BL/6.Tlr2(-/-) and C57BL/6.Tlr9(-/-) mice and C57BL/6.Tlr2/9(-/-) mice of both sexes. C57BL/6.Myd88(-/-) mice were completely protected. Lower clinical scores were associated with reduced leukocyte infiltrates. These results were confirmed by passive adoptive transfer of disease into female C57BL/6.Tlr2(-/-) and C57BL/6.Tlr9(-/-) mice, where protection in the absence of TLR2 was associated with fewer infiltrating CD4(+) cells in the CNS, reduced prevalence of detectable circulating IL-6, and increased proportions of central (CD62L(+)) CD4(+)CD25(+)Foxp3(+) regulatory T cells. These results provide a potential molecular mechanism for the observed effects of TLR signaling on the severity of autoimmune CNS inflammation.     

CD4+CD25+ T cell-dependent inhibition of autoimmunity in transgenic mice overexpressing human Bcl-2 in T lymphocytes

Regulation of lymphocyte survival is essential for the maintenance of lymphoid homeostasis preventing the development of autoimmune diseases. Recently, we described a systemic lupus erythematosus associated with an IgA nephropathy in autoimmune-prone (NZW x C57BL/6)F(1) overexpressing human Bcl-2 (hBcl-2) in B cells (transgenic (Tg) 1). In the present study, we analyze in detail a second line of hBcl-2 Tg mice overexpressing the transgene in all B cells and in a fraction of CD4(+) and CD8(+) T cells (Tg2). We demonstrate here that the overexpression of hBcl-2 in T cells observed in Tg2 mice is associated with a resistance to the development of lupus disease and collagen type II-induced arthritis in both (NZW x C57BL/6)F(1) and (DBA/1 x C57BL/6)F(1) Tg2 mice, respectively. The disease-protective effect observed in autoimmune-prone Tg2 mice is accompanied by an increase of peripheral CD4(+)CD25(+) hBcl-2(+) regulatory T cells (T(regs)), expressing glucocorticoid-induced TNFR, CTLA-4, and FoxP3. Furthermore, the in vivo depletion of CD4(+)CD25(+) T(regs) in (DBA/1 x C57BL/6)F(1) Tg2 mice promotes the development of a severe collagen type II-induced arthritis. Taken together, our results indicate that the overexpression of hBcl-2 in CD4(+) T cells alters the homeostatic mechanisms controlling the number of CD4(+)CD25(+) T(regs) resulting in the inhibition of autoimmune diseases.     

MHC-independent genetic factors control the magnitude of CD4+ T cell responses to amyloid-β peptide in mice through regulatory T cell-mediated inhibition

Accumulation of amyloid-β peptide (Aβ) is considered the triggering factor of pathogenic lesions in Alzheimer's disease (AD), and vaccines targeting Aβ are promising therapeutic options. However, the occurrence of meningoencephalitides attributed to T cell responses in 6% of Aβ-immunized patients underscores the need for a better understanding of T cell responses to Aβ. We characterized the parameters controlling the magnitude of Aβ-specific CD4(+) T cell responses in mice. T cell responsiveness to Aβ1-42 was highly heterogeneous between mouse strains of different H-2 haplotypes, with SJL/J (H-2(s)) mice displaying a strong response, mainly specific for Aβ10-24, and C57BL/6 (H-2(b)) mice displaying a weak response to Aβ16-30. Surprisingly, C57BL/6 mice congenic for the H-2(s) haplotype (B6.H-2(S)), which display a "permissive" MHC class II allele for presentation of the immunodominant Aβ10-24 epitope, showed a very weak CD4(+) T cell response to Aβ, suggesting that MHC-independent genes downmodulate Aβ-specific CD4(+) T cell responses in C57BL/6 background. Vaccine-induced CD4(+) T cell responses to Aβ were significantly enhanced in both C57BL/6 and B6.H-2(S) mice upon depletion of regulatory T cells (Tregs), whereas Treg-depleted SJL/J mice displayed unaltered Aβ-specific T cell responses. Finally, Treg depletion in C57BL/6 transgenic APPPS1 mice, a mouse model of AD, results in enhanced vaccine-induced CD4(+) T cell responses in AD compared with wild-type animals. We concluded that the magnitude of Aβ-specific CD4(+) T cell responses is critically controlled in both physiological and pathological settings by MHC-independent genetic factors that determine the overall potency of Aβ-specific Treg responses.