Where FoxP3‐dependent regulatory T cells impinge on the development of inflammatory arthritis

Objective

Regulatory T cells play a suppressive role in many autoimmune diseases and can potentially affect various steps in the progression of disease. The purpose of this study was to analyze the role of Treg cells in the control of arthritis development.

Methods

Using crosses and cell transfers, we tested the effect of the scurfy loss‐of‐function mutation of the Foxp3 gene in the K/BxN mouse model. In this model, arthritis develops as the result of the production of high levels of pathogenic autoantibodies.

Results

The absence of Treg cells in K/BxN mice led to faster and more aggressive arthritis. Strikingly, disease also spread to joints not normally affected in this model. The absence of Treg cells resulted in an acceleration of the immunologic phase of disease, with significantly earlier autoantibody production. However, the broadened spectrum of affected joints in Foxp3‐mutant mice was not due to the earlier appearance of autoantibodies and could not be reproduced by increasing the anti–glucose‐6‐phosphate isomerase antibody load, which demonstrates an impact of Treg cells on effector phase manifestations. In addition, FoxP3+,CD25+ Treg cells accumulated in inflamed joints, even in nontransgenic animals. This preferential localization mimics that in human arthritides and indicates a preferential homing/retention of Treg cells to sites of inflammation.

Conclusion

These results indicate that Treg cells play a role in antibody‐mediated arthritis at several levels. Treg cells are involved in constraining the immune phase of disease, as well as limiting the articular damage provoked by the pathogenic autoantibodies in terms of severity and of the range of affected joints, which may contribute to the limited distal predominance of many arthritides.

     

How defects in central tolerance impinge on a deficiency in regulatory T cells

Both central (thymic) and peripheral (nonthymic) mechanisms are important for the induction and maintenance of T cell tolerance. Mice with a defect in Foxp3, required for the generation and activity of CD4(+)CD25(+) regulatory T cells, exhibit massive lymphoproliferation and severe inflammatory infiltration of multiple organs, in particular the lungs, liver, and skin. We have explored how this phenotype is influenced by an additional defect in central tolerance induction, generated by either crossing in a null mutation of the Aire gene or substituting the nonobese diabetic (NOD) genetic background. The double-deficient mice had fulminant autoimmunity in very early life and a gravely shortened lifespan vis-à-vis single-deficient littermates. They showed massive lymphoproliferation and exacerbated inflammatory damage, particularly in the lungs and liver. Yet, the range of affected sites was not noticeably extended, and, surprisingly, many organs, or regions of organs, remained untouched, suggesting additional important mechanisms to enforce immunological self-tolerance.     

Migration and function of FoxP3+ regulatory T cells in the hematolymphoid system

FoxP3+ T cells play critical roles in regulation of the hematolymphoid system and prevention of autoimmunity. Many FoxP3+ T cells, generated in thymus as the result of T cell receptor (TCR) recognition of self antigens, preferentially migrate to secondary lymphoid tissues such as lymph nodes and spleen in a manner similar to conventional na?ve T cells. FoxP3+ T cells differentiated in the periphery acquire homing phenotype to bone marrow and nonlymphoid tissues. Consistently, lymphoid- and nonlymphoid-tissue-homing FoxP3+ T cell subsets express different trafficking and chemokine receptors. FoxP3+ T cells regulate hematopoiesis by limiting the activation of immune cells and their production of hematopoietic cytokines available for stem and progenitor cells. In mice deficient in FoxP3+ T cells, aberrant regulation of hematopoiesis including excessive myelopoiesis occurs. In transplantation of allogenic hematopoietic cells, FoxP3+ T cells selectively suppress harmful graft-vs-host disease (GVHD) but leave beneficial graft-vs-leukemia (GVL) activity intact. Therefore, FoxP3+ T cells play essential roles in regulation of the hematolymphoid system in health and diseases, and are likely to be utilized as effective therapeutics for many diseases in the hematolymphoid system in the future.     

Normalization of FoxP3(+) regulatory T cells in response to effective antiretroviral therapy

Regulatory T cells (Tregs) blunt uncontrolled immune responses. In advanced human immunodeficiency virus (HIV) infection, the total number of Tregs is decreased, but the proportion of T cells with a regulatory phenotype is highly variable. We studied CD4(+)CD25(+)FoxP3(+) T cells from patients successfully treated with combination antiretroviral therapy (ART). The proportion of CD4(+)CD25(+)FoxP3(+) cells transiently increased and then decreased from a median of 13% at baseline to 5.1% at 48 weeks, similar to values in normal subjects. These data suggest that with effective therapy, the regulatory cell numbers normalize, and that the inflammatory signals driving their production may also abate.     

Rapamycin selectively expands CD4+CD25+FoxP3+ regulatory T cells

Rapamycin is an immunosuppressive compound that is currently used to prevent acute graft rejection in humans. In addition, rapamycin has been shown to allow operational tolerance in murine models. However, a direct effect of rapamycin on T regulatory (Tr) cells, which play a key role in induction and maintenance of peripheral tolerance, has not been demonstrated so far. Here, we provide new evidence that rapamycin selectively expands the murine naturally occurring CD4(+)CD25(+)FoxP3(+) Tr cells in vitro. These expanded Tr cells suppress proliferation of syngeneic T cells in vitro and prevent allograft rejection in vivo. Interestingly, rapamycin does not block activation-induced cell death and proliferation of CD4(+) T cells in vitro. Based on this new mode of action, rapamycin can be used to expand CD4(+)CD25(+)FoxP3(+) Tr cells for ex vivo cellular therapy in T-cell-mediated diseases.     

Enhanced thymic selection of FoxP3+ regulatory T cells in the NOD mouse model of autoimmune diabetes

FoxP3(+)CD4(+) regulatory T cells (Tregs) play a key role in the maintenance of peripheral self-tolerance, and it has been suggested that diabetes-susceptible nonobese diabetic (NOD) mice are defective in the generation and numbers of Tregs. We found thymic selection of Tregs to be under genetic control. Fetal thymic organ cultures on the NOD background required 3- to 10-fold more antigen than corresponding cultures on the B6 background for optimal induction of Tregs, but once the threshold for induction was reached the NOD background yielded close to 10-fold more Tregs. This increased selection of Tregs was also found in nontransgenic NOD mice in fetal through adult stages. This trait did not map to the MHC, idd3, or the chromosome 3 (Chr3) regions that control clonal deletion, but mainly to two regions on Chr1 and Chr11. Thus, NOD mice do not have a global defect in the generation or maintenance of Tregs; if anything, they show the opposite.     

IL-9 induces differentiation of TH17 cells and enhances function of FoxP3+ natural regulatory T cells

The development of T helper (T_H)17 and regulatory T (T_reg) cells is reciprocally regulated by cytokines. Transforming growth factor (TGF)-β alone induces FoxP3⁺ T_reg cells, but together with IL-6 or IL-21 induces T_H17 cells. Here we demonstrate that IL-9 is a key molecule that affects differentiation of T_H17 cells and T_reg function. IL-9 predominantly produced by T_H17 cells, synergizes with TGF-β1 to differentiate naïve CD4⁺ T cells into T_H17 cells, while IL-9 secretion by T_H17 cells is regulated by IL-23. Interestingly, IL-9 enhances the suppressive functions of FoxP3⁺ CD4⁺ T_reg cells in vitro, and absence of IL-9 signaling weakens the suppressive activity of nT_regs in vivo, leading to an increase in effector cells and worsening of experimental autoimmune encephalomyelitis. The mechanism of IL-9 effects on T_H17 and T_regs is through activation of STAT3 and STAT5 signaling. Our findings highlight a role of IL-9 as a regulator of pathogenic versus protective mechanisms of immune responses.     

Identification of a chemokine network that recruits FoxP3(+) regulatory T cells into chronically inflamed intestine

BACKGROUND AND AIMS: It has been unclear which chemokine network is involved in migration of T-cell subsets to chronically inflamed lesions of the intestine. SAMP1/YP mice develop a spontaneous chronic transmural intestinal lesion specifically in the ileum. Using these mice, we investigated the gut chemokine network involved in specific migration of T-cell subsets to the inflamed lesion of the intestine. METHODS: We performed expression analyses of chemokines and their receptors, chemokine receptor blocking studies, and migration studies in vitro and in vivo to identify the gut chemokine network induced in intestinal inflammation and to determine its role in migration of conventional and FoxP3(+) suppressor T cells to the inflamed intestine. RESULTS: The expression of homeostatic chemokines was largely unchanged in the inflamed lesion of SAMP1/YP mice compared with control mice. However, an additional chemokine axis (CCL5-CCR5) was up-regulated in the inflamed intestine of SAMP1/YP mice compared with control mice. Activated T cells of SAMP1/YP mice compared with control mice were hyperresponsive to CCL5 in chemotaxis. CCR5(+) T cells preferentially migrated to the inflamed lesion, which can be blocked by a CCR5 antagonist. Importantly, the FoxP3(+) regulatory T cells of the inflamed lesion of SAMP1/YP mice highly expressed CCR5. CCR5 blockade suppressed the migration of FoxP3(+) T cells into the inflamed intestine and significantly exacerbated the intestinal inflammation. CONCLUSIONS: The CCL5-CCR5 chemokine axis is involved in preferential recruitment of FoxP3(+) regulatory T cells, which prevents further exacerbation of chronic inflammation in the intestine.     

Diversity of regulatory T cells to control arthritis

During follow-up of the suppressive functions of CD4+ T helper (Th) 2 cells in recent years, the suppressive capacities of newly recognised CD4+ Th cells with more widespread suppressive potential have been extensively investigated. These Th cells, collectively termed regulatory T cells, are characterised by the secretion of specific cytokines, such as interleukin (IL)-10 (Tr1 Th cells), transforming growth factor (TGF)beta (Th3 cells) or the constitutive expression of CD25 (naturally occurring T regulatory cells, nTregs). The balance of these regulatory T cells with pro-inflammatory effector T cells, such as Th1 (interferon (IFN)gamma secreting), Th17 (IL-17 secreting) and CD25- Th cells, has been shown to be of pivotal importance for the development and persistence of autoimmune diseases. The high potential of regulatory T cells (in particular nTregs), to efficiently suppress several arthritic responses both in humans and in animal models of arthritis, make them therapeutic targets of interest in arthritic conditions such as rheumatoid arthritis.     

Transforming growth factor beta induced FoxP3+ regulatory T cells suppress Th1 mediated experimental colitis

BACKGROUND AND AIMS: The imbalance between effector and regulatory T cells plays a central role in the pathogenesis of inflammatory bowel diseases. In addition to the thymus, CD4+CD25+ regulatory T cells can be induced in the periphery from a population of CD25- T cells by treatment with transforming growth factor beta (TGF-beta). Here, we analysed the in vivo function of TGF-beta induced regulatory T (Ti-Treg) cells in experimental colitis. METHODS: Ti-Treg cells were generated in cell culture in the presence or absence of TGF-beta and tested for their regulatory potential in experimental colitis using the CD4+CD62L+ T cell transfer model. RESULTS: Ti-Treg cells significantly suppressed Th1 mediated colitis on CD4+CD62L+ T cell transfer in vivo, as shown by high resolution endoscopy, histology, immunohistochemistry, and cytokine analysis. Further analysis of in vivo and in vitro expanded Ti-Treg cells showed that exogenous interleukin 2 (IL-2) was crucial for survival and expansion of these cells. CONCLUSION: Our data suggest that regulatory Ti-Treg cells expand by TGF-beta and exogenous IL-2 derived from effector T cells at the site of inflammation. In addition to Tr1 and thymic CD4+CD25+ T cells, peripheral Ti-Treg cells emerge as a class of regulatory T cells with therapeutic potential in T cell mediated chronic intestinal inflammation.