Promiscuous thymic expression of an autoantigen gene does not result in negative selection of pathogenic T cells

"Promiscuous" thymic expression of peripheral autoantigens can contribute to immunological tolerance in some cases. However, in this study we show that thymic mRNA expression alone cannot predict a contribution to thymic tolerance. Autoimmune gastritis is caused by CD4+ T cells directed to the alpha (H/Kalpha) and beta (H/Kbeta) subunits of the gastric membrane protein the H+/K+ ATPase. H/Kalpha mRNA is expressed in the thymus, but H/Kbeta expression is barely detectable. In this study, we demonstrate that thymic H/Kalpha in wild-type mice or mice that overexpressed H/Kalpha did not result in negative selection of pathogenic anti-H/Kalpha T cells. However, negative selection of anti-H/Kalpha T cells did occur if H/Kbeta was artificially overexpressed in the thymus. Given that H/Kalpha cannot be exported from the endoplasmic reticulum and is rapidly degraded in the absence of H/Kbeta, we conclude that H/Kalpha epitopes are unable to access MHC class II loading compartments in cells of the normal thymus. This work, taken together with our previous studies, highlights that thymic autoantigen expression does not necessarily result in the induction of tolerance.     

Endogenous H/K ATPase beta-subunit promotes T cell tolerance to the immunodominant gastritogenic determinant

A CD4(+) T cell response to the gastric H/K ATPase beta-subunit (H/Kbeta) is required for the onset of experimental autoimmune gastritis in BALB/c mice. The extent to which endogenous H/Kbeta contributes toward the tolerance of the H/Kbeta-specific T cell repertoire in normal individuals is not known. By comparison of T cell responses in H/Kbeta-deficient (o/o) and H/Kbeta-expressing BALB/c mice, in this work we show that the endogenous H/Kbeta autoantigen plays a major role in the tolerance of pathogenic H/Kbeta-specific T cells. First, T cell-dependent Ab responses to the H/Kbeta Ag were enhanced in H/K ATPase-immunized H/Kbeta-deficient mice compared with wild-type mice. Second, peptide immunization experiments indicated that immune responses to the major gastritogenic epitope of the H/K ATPase, namely H/Kbeta(253-277), were significantly more vigorous in H/Kbeta-deficient mice compared with wild-type mice. Third, unfractionated splenocytes from H/Kbeta-deficient mice, but not H/Kbeta-expressing mice, induced autoimmune gastritis after adoptive transfer to BALB/c nude mice. The enhanced responses to H/Kbeta in H/Kbeta-deficient mice were shown to be intrinsic to CD4(+)CD25(-) T cells rather than a change in status of CD4(+)CD25(+) regulatory T cells. We conclude from these studies that the H/Kbeta-specific T cells in wild-type mice represent the residue of a T cell repertoire, directed toward a single determinant, that has been subjected to partial tolerance induction.     

The role of CD4+CD25+ immunoregulatory T cells in the induction of autoimmune gastritis

A number of experimental models of organ-specific autoimmunity involve a period of peripheral lymphopenia prior to disease onset. There is now considerable evidence that the development of autoimmune disease in these models is due to the absence of CD4+CD25+ regulatory T cells. However, the role of CD4+CD25+ regulatory T cells in the prevention of autoimmune disease in normal individuals has not been defined. Here we have assessed the affect of depletion of CD4+CD25+ regulatory T cells in BALB/c mice on the induction of autoimmune gastritis. The CD4+CD25+ T cell population was reduced to 95% of the original population in adult thymectomized mice by treatment with anti-CD25 mAb. By 48 days after the anti-CD25 treatment, the CD4+CD25+ regulatory T cell population had returned to a normal level. Treatment of thymectomized adult mice for up to 4 weeks with anti-CD25 mAb did not result in the development of autoimmune gastritis. Furthermore, we have demonstrated that depletion of CD4+CD25+ regulatory T cells, together with transient CD4+ T lymphopenia, also did not result in the development of autoimmune gastritis, indicating that peripheral expansion of the CD4+ T cell population, per se, does not result in autoimmunity in adult mice. On the other hand, depletion of CD4+CD25+ T cells in 10-day-old euthymic mice resulted in a 30% incidence of autoimmune gastritis. These data suggest that CD4+CD25+ regulatory T cells may be important in protection against autoimmunity while the immune system is being established in young animals, but subsequently other factors are required to initiate autoimmunity.     

TCR-mediated involvement of CD4+ transgenic T cells in spontaneous inflammatory bowel disease in lymphopenic mice.

Spontaneous colitis resembling ulcerative colitis developed in 3 of 10 independent TCR transgenic (Tg) mouse lines maintained under specific pathogen-free conditions. All three susceptible lines were CD4 lymphopenic, whereas resistant lines had normal numbers of CD4+ T cells. Thus, cytochrome c-specific 5C.C7 TCR Tg mice developed colitis only when crossed onto a SCID- or Rag-1-deficient background. A second line of lymphopenic cytochrome c-specific Tg mice bearing the AND TCR also developed colitis. In both cases, CD4+ T cells expressing the Tg-encoded TCR were preferentially activated in inflamed colons compared with lymph nodes or spleens. In contrast, Tg+CD4+ T cells remained quiescent in both inflamed and unaffected colons in another line of susceptible Tg mice carrying a TCR specific for myelin basic protein, suggesting a fortuitous cross-reactivity of the IEk-restricted cytochrome c-reactive AND and 5C.C7 TCRs with an Ag present in the gut. The percentage of CD4+ T cells expressing only endogenous TCR alpha-chains was increased consistently in inflamed colons in AND as well as 5C.C7 Rag-1-/- TCR Tg mice, suggesting that polyclonal CD4+ T cells were also involved in the pathogenesis of spontaneous colitis. Moreover, our data indicate that some alpha-chain rearrangement was still occurring in TCR Tg mice on a Rag-1-/- background, since activated CD4+ T cells expressing endogenously rearranged alpha-chains paired with the Tg-encoded beta-chain were detected consistently in the colons of such mice.     

Suppressor effector function of CD4+CD25+ immunoregulatory T cells is antigen nonspecific

CD4+CD25+ T cells represent a unique population of "professional" suppressor T cells that prevent induction of organ-specific autoimmune disease. In vitro, CD4+CD25+ cells were anergic to simulation via the TCR and when cultured with CD4+CD25- cells, markedly suppressed polyclonal T cell proliferation by specifically inhibiting the production of IL-2. Suppression was cytokine independent, cell contact dependent, and required activation of the suppressors via their TCR. Further characterization of the CD4+CD25+ population demonstrated that they do not contain memory or activated T cells and that they act through an APC-independent mechanism. CD4+CD25+ T cells isolated from TCR transgenic (Tg) mice inhibited responses of CD4+CD25- Tg T cells to the same Ag, but also inhibited the Ag-specific responses of Tg cells specific for a distinct Ag. Suppression required that both peptide/MHC complexes be present in the same culture, but the Ags could be presented by two distinct populations of APC. When CD4+CD25+ T cells were cultured with anti-CD3 and IL-2, they expanded, remained anergic, and in the absence of restimulation via their TCR, suppressed Ag-specific responses of CD4+CD25- T cells from multiple TCR transgenics. Collectively, these data demonstrate that CD4+CD25+ T cells require activation via their TCR to become suppressive, but once activated, their suppressor effector function is completely nonspecific. The cell surface molecules involved in this T-T interaction remain to be characterized.     

CD4+CD25+ T cells prevent the development of organ-specific autoimmune disease by inhibiting the differentiation of autoreactive effector T cells

Thymic-derived, naturally occurring, CD4+CD25+ regulatory T cells (nTreg) are potent suppressors of immune responses. A detailed understanding of which components of the development and activation of pathogenic effector T cells are inhibited by nTreg during the course of T cell-mediated, organ-specific autoimmunity is as yet unknown. We have analyzed the effects of polyclonal nTreg on the development of autoimmune gastritis. The nTreg inhibited the development of disease, but failed to inhibit the migration of effector cells into the gastric lymph node or stomach. Notably, nTreg did not inhibit the expansion of autoreactive T cells in the gastric lymph node. The primary effect of nTreg appeared to be inhibition of differentiation of autoantigen-specific T cells to Th1 effector cells, as reflected by a decrease in Ag-stimulated IFN-gamma production and a reduction in T-bet expression.     

Rapamycin promotes expansion of functional CD4+CD25+FOXP3+ regulatory T cells of both healthy subjects and type 1 diabetic patients

CD4+CD25+FOXP3+ T regulatory cells (Tregs) are pivotal for the induction and maintenance of peripheral tolerance in both mice and humans. Rapamycin has been shown to promote tolerance in experimental models and to favor CD4+CD25+ Treg-dependent suppression. We recently reported that rapamycin allows in vitro expansion of murine CD4+CD25+FoxP3+ Tregs, which preserve their suppressive function. In the current study, we show that activation of human CD4+ T cells from healthy subjects in the presence of rapamycin leads to growth of CD4+CD25+FOXP3+ Tregs and to selective depletion of CD4+CD25- T effector cells, which are highly sensitive to the antiproliferative effect of the compound. The rapamycin-expanded Tregs suppress proliferation of both syngeneic and allogeneic CD4+ and CD8+ T cells. Interestingly, rapamycin promotes expansion of functional CD4+CD25+FOXP3+ Tregs also in type 1 diabetic patients, in whom a defect in freshly isolated CD4+CD25+ Tregs has been reported. The capacity of rapamycin to allow growth of functional CD4+CD25+FOXP3+ Tregs, but also to deplete T effector cells, can be exploited for the design of novel and safe in vitro protocols for cellular immunotherapy in T cell-mediated diseases.     

The IL-4 receptor alpha-chain-binding cytokines, IL-4 and IL-13, induce forkhead box P3-expressing CD25+CD4+ regulatory T cells from CD25-CD4+ precursors

The mechanisms underlying the extrathymic generation of CD25+CD4 regulatory T cells (Tregs) are largely unknown. In this study the IL-4R alpha-chain-binding cytokines, IL-4 and IL-13, were identified as inducers of CD25+ Tregs from peripheral CD25-CD4 naive T cells. IL-4-induced CD25+ Tregs phenotypically and functionally resemble naturally occurring Tregs in that they are anergic to mitogenic stimulation, inhibit the proliferation of autologous responder T cells, express high levels of the Forkhead box P3 and the surface receptors glucocorticoid-induced TNFR family-related protein and CTLA-4, and inhibit effector T cells in a contact-dependent, but cytokine-independent, manner. The IL-4-induced generation of peripheral Tregs was independent of the presence of TGF-beta or IL-10, but was dependent on Ag-specific stimulation and B7 costimulation. The significance of the IL-4Ralpha-binding cytokines in the generation of Ag-specific Tregs was emphasized in a mouse model of oral tolerance, in which neutralization of IL-4 and IL-13 in mice transgenic for the TCR specific for OVA completely inhibited the expansion of OVA-specific Tregs that can be induced in untreated mice by feeding the nominal Ag. Together, our results demonstrate that IL-4 and IL-13 play an important role in generating Forkhead box P3-expressing CD25+ Tregs extrathymically in an Ag-dependent manner and therefore provide an intriguing link between the well-established immunoregulatory capacity of Th2 cells and the powerful CD25+ Treg population. Moreover, our findings might provide the basis for the design of novel therapeutic approaches for targeted immunotherapy with Tregs to known Ags in autoimmune diseases or graft-vs-host reactions.     

Cyclophosphamide-induced type-1 diabetes in the NOD mouse is associated with a reduction of CD4+CD25+Foxp3+ regulatory T cells

Regulatory T cells (Tregs) have been implicated as key players in immune tolerance as well as suppression of antitumor responses. The chemotherapeutic alkylating agent cyclophosphamide (CY) is widely used in the treatment of tumors and some autoimmune conditions. Although previous data has demonstrated that Tregs may be preferentially affected by CY, its relevance in promoting autoimmune conditions has not been addressed. The nonobese diabetic mouse spontaneously develops type-1 diabetes (T1D). We demonstrate in this study that CY targets CD4+CD25+Foxp3+ Tregs in vivo. CD4+CD25+ T cells isolated from CY-treated mice display reduced suppressive activity in vitro and increased expression of apoptotic markers. Although Treg numbers rapidly recovered to pretreatment levels in the peripheral lymphoid tissues, Tregs failed to recover proportionally within pancreatic infiltrates. T1D progression was effectively prevented by adoptive transfer of a small number of islet Ag-specific CD4+CD25+ Tregs to CY-treated recipients. Prevention of T1D was associated with reduced T cell activation and higher Treg proportions in the pancreas. We conclude that acceleration of T1D by CY is associated with a reduction in CD4+CD25+Foxp3+ Tregs and can be prevented by transfer of CD4+CD25+ Tregs.     

Increased natural CD4+CD25+ regulatory T cells and their suppressor activity do not contribute to mortality in murine polymicrobial sepsis

Regulatory T cells (Tregs), including natural CD4+CD25+ Tregs and inducible IL-10 producing T regulatory type 1 (T(R)1) cells, maintain tolerance and inhibit autoimmunity. Recently, increased percentages of Tregs have been observed in the blood of septic patients, and ex vivo-activated Tregs were shown to prevent polymicrobial sepsis mortality. Whether endogenous Tregs contribute to sepsis outcome remains unclear. Polymicrobial sepsis, induced by cecal ligation and puncture, caused an increased number of splenic Tregs compared with sham-treated mice. Splenic CD4+CD25+ T cells from septic mice expressed higher levels of Foxp3 mRNA and were more efficient suppressors of CD4+CD25- T effector cell proliferation. Isolated CD4+ T cells from septic mice displayed increased intracellular IL-10 staining following stimulation, indicating that T(R)1 cells may also be elevated in sepsis. Surprisingly, Ab depletion of total CD4+ or CD4+CD25+ populations did not affect mortality. Furthermore, no difference in survival outcome was found between CD25 or IL-10 null mice and wild-type littermates, indicating that Treg or T(R)1-generated IL-10 are not required for survival. These results demonstrate that, although sepsis causes a relative increase in Treg number and increases their suppressive function, their presence does not contribute significantly to overall survival in this model.     

Thymic expression of a gastritogenic epitope results in positive selection of self-reactive pathogenic T cells

Intrathymic expression of tissue-specific self-Ags can mediate tolerance of self-reactive T cells. However, in this study we define circumstances by which thymic expression of a tissue-specific autoepitope enhances positive selection of disease-causing, self-reactive T cells. An immunodominant gastritogenic epitope, namely the gastric H/K ATPase beta subunit(253-277) (H/Kbeta(253-277)), was attached to the C terminus of the invariant chain (Ii) and the hybrid Ii (Ii-H/Kbeta(253-277)) expressed in mice under control of the Ii promoter. The Ii-H/Kbeta(253-277) fusion protein was localized to MHC class II-expressing cells in the thymus and periphery of Ii-H/Kbeta(253-277) transgenic mice. In one transgenic line the level of presentation in the periphery (spleen) was insufficient to activate naive, low affinity H/Kbeta(253-277)-specific transgenic T cells (1E4-TCR), whereas thymic presentation of H/Kbeta(253-277) enhanced positive selection of 1E4-TCR cells in Ii-H/Kbeta(253-277)/1E4-TCR double-transgenic mice. Furthermore, Ii-H/Kbeta(253-277)/1E4-TCR double-transgenic mice had an increased incidence of autoimmune gastritis compared with 1E4-TCR single-transgenic mice, demonstrating that the 1E4 T cells that seeded the periphery of Ii-H/Kbeta(253-277) mice were pathogenic. Therefore, low levels of tissue-specific Ags in the thymus can result in positive selection of low avidity, self-reactive T cells. These findings also suggest that the precise level of tissue-specific Ags in the thymus may be an important consideration in protection against autoimmune disease and that perturbation of the levels of self-Ags may be detrimental.     

Influence of CD4+CD25+ regulatory T cells on low/high-avidity CD4+ T cells following peptide vaccination

We have recently reported that NY-ESO-1-specific naive CD4+ T cell precursors exist in most individuals but are suppressed by CD4+CD25+ regulatory T cells (Tregs), while memory CD4+ T cell effectors against NY-ESO-1 are found only in cancer patients with spontaneous Ab responses to NY-ESO-1. In this study, we have analyzed mechanisms of CD4+ T cell induction following peptide vaccination in relation to susceptibility to Tregs. Specific HLA-DP4-restricted CD4+ T cell responses were elicited after vaccination with NY-ESO-1(157-170) peptide (emulsified in IFA) in patients with NY-ESO-1-expressing epithelial ovarian cancer. These vaccine-induced CD4+ T cells were detectable from effector/memory populations without requirement for in vitro CD4+CD25+ T cell depletion. However, they were only able to recognize NY-ESO-1(157-170) peptide but not naturally processed NY-ESO-1 protein and had much lower avidity compared with NY-ESO-1-specific pre-existing naive CD4+CD25- T cell precursors or spontaneously induced CD4+ T cell effectors of cancer patients with NY-ESO-1 Ab. We propose that vaccination with NY-ESO-1(157-170) peptide recruits low-avidity T cells with low sensitivity to Tregs and fails to modulate the suppressive effect of Tregs on high-avidity NY-ESO-1-specific T cell precursors.     

In vitro suppression of CD8+ T cell function by Friend virus-induced regulatory T cells

Regulatory T cell (Treg)-mediated suppression of CD8+ T cells has been implicated in the establishment and maintenance of chronic viral infections, but little is known about the mechanism of suppression. In this study an in vitro assay was developed to investigate the suppression of CD8+ T cells by Friend retrovirus (FV)-induced Tregs. CD4+CD25+ T cells isolated from mice chronically infected with the FV suppressed the development of effector function in naive CD8+ T cells without affecting their ability to proliferate or up-regulate activation markers. In vitro restimulation was not required for suppression by FV-induced Tregs, correlating with their high activation state in vivo. Suppression was mediated by direct T cell-T cell interactions and occurred in the absence of APCs. Furthermore, suppression occurred irrespective of the TCR specificity of the CD8+ T cells. Most interestingly, FV-induced Tregs were able to suppress the function of CD8+ effector T cells that had been physiologically activated during acute FV infection. The ability to suppress the effector function of activated CTLs is likely a requisite role for Tregs in limiting immunopathology by CD8+ T cells during antiviral immune responses. Such activity may also have adverse consequences by allowing viruses to establish and maintain chronic infections if suppression of antiviral immune responses occurs before virus eradication.     

Experience-driven development: effector/memory-like alphaE+Foxp3+ regulatory T cells originate from both naive T cells and naturally occurring naive-like regulatory T cells

Naturally occurring Foxp3+CD25+CD4+ regulatory T cells (Treg) have initially been described as anergic cells; however, more recent in vivo studies suggest that Tregs vigorously proliferate under both homeostatic as well as inflammatory conditions. We have previously identified a subset of murine CD4+ Tregs, which is characterized by expression of the integrin alphaEbeta7 and which displays an effector/memory-like phenotype indicative of Ag-specific expansion and differentiation. In the present study, the alphaE+ Treg subset was found to contain a large fraction of cycling cells under homeostatic conditions in healthy mice. Using an adoptive transfer system of Ag-specific T cells, we could demonstrate that the vast majority of transferred natural, naive-like CD25+CD4+ Tregs acquired expression of the integrin alphaEbeta7 upon tolerogenic application of Ag via the oral route. In addition, using the same system, Foxp3+ Tregs could be de novo induced from conventional naive CD25-CD4+ T cells, and this conversion was associated with concomitant expression of alphaE. These findings suggest that Tregs expressing the integrin alphaE are effector/memory Tregs with a high turnover rate that can develop in the periphery upon Ag contact under tolerogenic conditions, both from thymic-derived CD25+CD4+ Tregs with a naive-like phenotype as well as from conventional naive T cells.     

IL-12R beta 2 promotes the development of CD4+CD25+ regulatory T cells

We have previously shown that mice lacking the IL-12-specific receptor subunit beta2 (IL-12Rbeta2) develop more severe experimental autoimmune encephalomyelitis than wild-type (WT) mice. The mechanism underlying this phenomenon is not known; nor is it known whether deficiency of IL-12Rbeta2 impacts other autoimmune disorders similarly. In the present study we demonstrate that IL-12Rbeta2(-/-) mice develop earlier onset and more severe disease in the streptozotocin-induced model of diabetes, indicating predisposition of IL-12Rbeta2-deficient mice to autoimmune diseases. T cells from IL-12Rbeta2(-/-) mice exhibited significantly higher proliferative responses upon TCR stimulation. The numbers of naturally occurring CD25(+)CD4(+) regulatory T cells (Tregs) in the thymus and spleen of IL-12Rbeta2(-/-) mice were comparable to those of WT mice. However, IL-12Rbeta2(-/-) mice exhibited a significantly reduced capacity to develop Tregs upon stimulation with TGF-beta, as shown by significantly lower numbers of CD25(+)CD4(+) T cells that expressed Foxp3. Functionally, CD25(+)CD4(+) Tregs derived from IL-12Rbeta2(-/-) mice were less efficient than those from WT mice in suppressing effector T cells. The role of IL-12Rbeta2 in the induction of Tregs was confirmed using small interfering RNA. These findings suggest that signaling via IL-12Rbeta2 regulates both the number and functional maturity of Treg cells, which indicates a novel mechanism underlying the regulation of autoimmune diseases by the IL-12 pathway.     

Suppression of CD4+ T lymphocyte effector functions by CD4+CD25+ cells in vivo

CD4+CD25+ regulatory T cells have been extensively studied during the last decade, but how these cells exert their regulatory function on pathogenic effector T cells remains to be elucidated. Naive CD4+ T cells transferred into T cell-deficient mice strongly expand and rapidly induce inflammatory bowel disease (IBD). Onset of this inflammatory disorder depends on IFN-gamma production by expanding CD4+ T cells. Coinjection of CD4+CD25+ regulatory T cells protects recipient mice from IBD. In this study, we show that CD4+CD25+ regulatory T cells do not affect the initial activation/proliferation of injected naive T cells as well as their differentiation into Th1 effectors. Moreover, naive T cells injected together with CD4+CD25+ regulatory T cells into lymphopenic hosts are still able to respond to stimuli in vitro when regulatory T cells are removed. In these conditions, they produce as much IFN-gamma as before injection or when injected alone. Finally, when purified, they are able to induce IBD upon reinjection into lymphopenic hosts. Thus, prevention of IBD by CD4+CD25+ regulatory T cells is not due to deletion of pathogenic T cells, induction of a non reactive state (anergy) among pathogenic effector T cells, or preferential induction of Th2 effectors rather than Th1 effectors; rather, it results from suppression of T lymphocyte effector functions, leading to regulated responses to self.     

CD18 is required for optimal development and function of CD4+CD25+ T regulatory cells

CD4+CD25+ T regulatory (Treg) cells inhibit immunopathology and autoimmune disease in vivo. CD4+CD25+ Treg cells' capacity to inhibit conventional T cells in vitro is dependent upon cell-cell contact; however, the cell surface molecules mediating this cell:cell contact have not yet been identified. LFA-1 (CD11a/CD18) is an adhesion molecule that plays an established role in T cell-mediated cell contact and in T cell activation. Although expressed at high levels on murine CD4+CD25+ Treg cells, the role of LFA-1 in these cells has not been defined previously. We hypothesized that LFA-1 may play a role in murine CD4+CD25+ Treg function. To evaluate this, we analyzed LFA-1-deficient (CD18-/-) CD4+CD25+ T cells. We show that CD18-/- mice demonstrate a propensity to autoimmunity. Absence of CD18 led to diminished CD4+CD25+ T cell numbers and affected both thymic and peripheral development of these cells. LFA-1-deficient CD4+CD25+ T cells were deficient in mediating suppression in vitro and in mediating protection from colitis induced by the transfer of CD4+CD25- T cells into lymphopenic hosts. Therefore, we define a crucial role for CD18 in optimal CD4+CD25+ Treg development and function.     

Cross-primed CD8+ cytotoxic T cells induce severe Helicobacter-associated gastritis in the absence of CD4+ T cells

BACKGROUND: Although previous studies have reported important roles of CD4(+) type 1-helper T cells and regulatory T cells in Helicobacter-associated gastritis, the significance of CD8(+) cytotoxic T cells remains unknown. To study the roles of CD8(+) T cells, we examined the immune response in the gastric mucosa of Helicobacter felis-infected major histocompatibility complex (MHC) class II-deficient (II(-/-)) mice, which lack CD4(+) T cells. MATERIALS AND METHODS: Stomachs from H. felis-infected wild-type and infected MHC II(-/-) mice were examined histologically and immunohistochemically. Gastric acidity and serum levels of anti-H. felis antibodies were measured. The expression of pro-inflammatory and anti-inflammatory cytokine, Fas-ligand, perforin, and Foxp3 genes in the gastric mucosa was investigated. RESULTS: H. felis-infected MHC II(-/-) mice developed severe gastritis, accompanied by marked infiltration of CD8(+) cells. At 1 and 2 months after inoculation, mucosal inflammation and atrophy were more severe in MHC II(-/-) mice, although gastritis had reached similar advanced stages at 3 months after inoculation. There was little infiltration of CD4(+) cells, and no Foxp3-positive cells were detected in the gastric mucosa of the infected MHC II(-/-) mice. The expression of the interleukin-1beta and Fas-ligand genes was up regulated, but that of Foxp3 was down regulated in the infected MHC II(-/-) mice. Serum levels of anti-H. felis antibodies were lower in the infected MHC II(-/-) mice, despite severe gastritis. CONCLUSIONS: The present study suggests that cross-primed CD8(+) cytotoxic T cells can induce severe H.-associated gastritis in the absence of CD4(+) helper T cells and that Foxp3-positive cells may have an important role in the control of gastric 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.