Despite increased CD4+Foxp3+ cells within the infection site, BALB/c IL-4 receptor-deficient mice reveal CD4+Foxp3-negative T cells as a source of IL-10 in Leishmania major susceptibility

BALB/c IL-4Ralpha(-/-) mice, despite the absence of IL-4/IL-13 signaling and potent Th2 responses, remain highly susceptible to Leishmania major substain LV39 due exclusively to residual levels of IL-10. To address the contribution of CD4(+)CD25(+) T regulatory (Treg) cells to IL-10-mediated susceptibility, we depleted CD4(+)CD25(+) cells in vivo and reconstituted IL-4Ralpha x RAG2 recipients with purified CD4(+)CD25(-) T cells. Although anti-CD25 mAb treatment significantly decreased parasite numbers in IL-4Ralpha(-/-) mice, treatment with anti-IL-10R mAb virtually eliminated L. major parasites in both footpad and dermal infection sites. In addition, IL-4Ralpha x RAG2 mice reconstituted with CD4(+) cells depleted of CD25(+) Treg cells remained highly susceptible to infection. Analysis of L. major-infected BALB/c and IL-4Ralpha(-/-) inflammatory sites revealed that the majority of IL-10 was secreted by the CD4(+)Foxp3(-) population, with a fraction of IL-10 coming from CD4(+)Foxp3(+) Treg cells. All T cell IFN-gamma production was also derived from the CD4(+)Foxp3(-) population. Nevertheless, the IL-4Ralpha(-/-)-infected ear dermis, but not draining lymph nodes, consistently displayed 1.5- to 2-fold greater percentages of CD4(+)CD25(+) and CD4(+)Foxp3(+) Treg cells compared with the BALB/c-infected dermis. Thus, CD4(+)Foxp3(-) T cells are a major source of IL-10 that disrupts IFN-gamma activity in L. major-susceptible BALB/c mice. However, the increase in CD4(+)Foxp3(+) T cells within the IL-4Ralpha(-/-) dermis implies a possible IL-10-independent role for Treg cells within the infection site, and may indicate a novel immune escape mechanism used by L. major parasites in the absence of IL-4/IL-13 signaling.     

IL-17+ regulatory T cells in the microenvironments of chronic inflammation and cancer

Foxp3(+)CD4(+) regulatory T (Treg) cells inhibit immune responses and temper inflammation. IL-17(+)CD4(+) T (Th17) cells mediate inflammation of autoimmune diseases. A small population of IL-17(+)Foxp3(+)CD4(+) T cells has been observed in peripheral blood in healthy human beings. However, the biology of IL-17(+)Foxp3(+)CD4(+) T cells remains poorly understood in humans. We investigated their phenotype, cytokine profile, generation, and pathological relevance in patients with ulcerative colitis. We observed that high levels of IL-17(+)Foxp3(+)CD4(+) T cells were selectively accumulated in the colitic microenvironment and associated colon carcinoma. The phenotype and cytokine profile of IL-17(+)Foxp3(+)CD4(+) T cells was overlapping with Th17 and Treg cells. Myeloid APCs, IL-2, and TGF-β are essential for their induction from memory CCR6(+) T cells or Treg cells. IL-17(+)Foxp3(+)CD4(+) T cells functionally suppressed T cell activation and stimulated inflammatory cytokine production in the colitic tissues. Our data indicate that IL-17(+)Foxp3(+) cells may be "inflammatory" Treg cells in the pathological microenvironments. These cells may contribute to the pathogenesis of ulcerative colitis through inducing inflammatory cytokines and inhibiting local T cell immunity, and in turn may mechanistically link human chronic inflammation to tumor development. Our data therefore challenge commonly held beliefs of the anti-inflammatory role of Treg cells and suggest a more complex Treg cell biology, at least in the context of human chronic inflammation and associated carcinoma.     

IL-2 simultaneously expands Foxp3+ T regulatory and T effector cells and confers resistance to severe tuberculosis (TB): implicative Treg-T effector cooperation in immunity to TB

The possibility that simultaneous expansion of T regulatory cells (Treg) and T effector cells early postinfection can confer some immunological benefits has not been studied. In this study, we tested the hypothesis that early, simultaneous cytokine expansion of Treg and T effector cells in a tissue infection site can allow these T cell populations to act in concert to control tissue inflammation/damage while containing infection. IL-2 treatments early after Mycobacterium tuberculosis infection of macaques induced simultaneous expansion of CD4(+)CD25(+)Foxp3(+) Treg, CD8(+)CD25(+)Foxp3(+) T cells, and CD4(+) T effector/CD8(+) T effector/Vγ2Vδ2 T effector populations producing anti-M. tuberculosis cytokines IFN-γ and perforin, and conferred resistance to severe TB inflammation and lesions. IL-2-expanded Foxp3(+) Treg readily accumulated in pulmonary compartment, but despite this, rapid pulmonary trafficking/accumulation of IL-2-activated T effector populations still occurred. Such simultaneous recruitments of IL-2-expanded Treg and T effector populations to pulmonary compartment during M. tuberculosis infection correlated with IL-2-induced resistance to TB lesions without causing Treg-associated increases in M. tuberculosis burdens. In vivo depletion of IL-2-expanded CD4(+)Foxp3(+) Treg and CD4(+) T effectors during IL-2 treatment of M. tuberculosis-infected macaques significantly reduced IL-2-induced resistance to TB lesions, suggesting that IL-2-expanded CD4(+) T effector cells and Treg contributed to anti-TB immunity. Thus, IL-2 can simultaneously activate and expand T effector cells and Foxp3(+) Treg populations and confer resistance to severe TB without enhancing M. tuberculosis infection.     

Inducible adeno-associated virus-mediated IL-2 gene therapy prevents autoimmune diabetes

IL-2 and TGF-β1 play key roles in the immunobiology of Foxp3-expressing CD25(+)CD4(+) T cells (Foxp3(+)Treg). Administration of these cytokines offers an appealing approach to manipulate the Foxp3(+)Treg pool and treat T cell-mediated autoimmunity such as type 1 diabetes. However, efficacy of cytokine treatment is dependent on the mode of application, and the potent pleiotropic effects of cytokines like IL-2 may lead to severe side effects. In the current study, we used a gene therapy-based approach to assess the efficacy of recombinant adeno-associated virus vectors expressing inducible IL-2 or TGF-β1 transgenes to suppress ongoing β cell autoimmunity in NOD mice. Intramuscular vaccination of recombinant adeno-associated virus to 10-wk-old NOD female mice and a subsequent 3 wk induction of IL-2 was sufficient to prevent diabetes and block the progression of insulitis. Protection correlated with an increased frequency of Foxp3(+)Treg in the periphery as well as in the draining pancreatic lymph nodes and islets. IL-2 induced a shift in the ratio favoring Foxp3(+)Treg versus IFN-γ-expressing T cells infiltrating the islets. Induction of IL-2 had no systemic effect on the frequency or activational status of T cells and NK cells. Induction of TGF-β1 had no effect on the Foxp3(+)Treg pool or the progression of β cell autoimmunity despite induced systemic levels of activated TGF-β1 that were comparable to IL-2. These results demonstrate that inducible IL-2 gene therapy is an effective and safe approach to manipulate Foxp3(+)Treg and suppress T cell-mediated autoimmunity and that under the conditions employed, IL-2 is more potent than TGF-β1.     

Increased Th17 and regulatory T cell responses in EBV-induced gene 3-deficient mice lead to marginally enhanced development of autoimmune encephalomyelitis

EBV-induced gene 3 (EBI3)-encoded protein can form heterodimers with IL-27P28 and IL-12P35 to form IL-27 and IL-35. IL-27 and IL-35 may influence autoimmunity by inhibiting Th17 differentiation and facilitating the inhibitory roles of Foxp3(+) regulatory T (Treg) cells, respectively. In this study, we have evaluated the development of experimental autoimmune encephalomyelitis (EAE) in EBI3-deficient mice that lack both IL-27 and IL-35. We found that myelin oligodendrocyte glycoprotein peptide immunization resulted in marginally enhanced EAE development in EBI3-deficient C57BL6 and 2D2 TCR-transgenic mice. EBI3 deficiency resulted in significantly increased Th17 and Th1 responses in the CNS and increased T cell production of IL-2 and IL-17 in the peripheral lymphoid organs. EBI3-deficient and -sufficient 2D2 T cells had equal ability in inducing EAE in Rag1(-/-) mice; however, more severe disease was induced in EBI3(-/-)Rag1(-/-) mice than in Rag1(-/-) mice by 2D2 T cells. EBI3-deficient mice had increased numbers of CD4(+)Foxp3(+) Treg cells in peripheral lymphoid organs. More strikingly, EBI3-deficient Treg cells had more potent suppressive functions in vitro and in vivo. Thus, our data support an inhibitory role for EBI3 in Th17, Th1, IL-2, and Treg responses. Although these observations are consistent with the known functions of IL-27, the IL-35 contribution to the suppressive functions of Treg cells is not evident in this model. Increased Treg responses in EBI3(-/-) mice may explain why the EAE development is only modestly enhanced compared with wild-type mice.     

An in vivo IL-7 requirement for peripheral Foxp3+ regulatory T cell homeostasis

All T cells are dependent on IL-7 for their development and for homeostasis. Foxp3(+) regulatory T cells (Tregs) are unique among T cells in that they are dependent on IL-2. Whether such IL-2 dependency is distinct from or in addition to an IL-7 requirement has been a confounding issue, particularly because of the absence of an adequate experimental system to address this question. In this study, we present a novel in vivo mouse model where IL-2 expression is intact but IL-7 expression was geographically limited to the thymus. Consequently, IL-7 is not available in peripheral tissues. Such mice were generated by introducing a thymocyte-specific IL-7 transgene onto an IL-7 null background. In these mice, T cell development in the thymus, including Foxp3(+) Treg numbers, was completely restored, which correlates with the thymus-specific expression of transgenic IL-7. In peripheral cells, however, IL-7 expression was terminated, which resulted in a general paucity of T cells and a dramatic reduction of Foxp3(+) Treg numbers. Loss of Tregs was further accompanied by a significant reduction in Foxp3(+) expression levels. These data suggest that peripheral IL-7 is not only necessary for Treg survival but also for upregulating Foxp3 expression. Collectively, we assessed the effect of a selective peripheral IL-7 deficiency in the presence of a fully functional thymus, and we document a critical requirement for in vivo IL-7 in T cell maintenance and specifically in Foxp3(+) cell homeostasis.     

Preferential development of CD4 and CD8 T regulatory cells in RasGRP1-deficient mice

RasGRP1 and Sos are two Ras-guanyl-nucleotide exchange factors that link TCR signal transduction to Ras and MAPK activation. Recent studies demonstrate positive selection of developing thymocytes is crucially dependent on RasGRP1, whereas negative selection of autoreactive thymocytes appears to be RasGRP1 independent. However, the role of RasGRP1 in T regulatory (Treg) cell development and function is unknown. In this study, we characterized the development and function of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD44(high)CD122(+) Treg lineages in RasGRP1(-/-) mice. Despite impaired CD4 Treg cell development in the thymus, the periphery of RasGRP1(-/-) mice contained significantly increased frequencies of CD4(+)Foxp3(+) Treg cells that possessed a more activated cell surface phenotype. Furthermore, on a per cell basis, CD4(+)Foxp3(+) Treg cells from mutant mice are more suppressive than their wild-type counterparts. Our data also suggest that the lymphopenic environment in the mutant mice plays a dominant role of favored peripheral development of CD4 Treg cells. These studies suggest that whereas RasGRP1 is crucial for the intrathymic development of CD4 Treg cells, it is not required for their peripheral expansion and function. By contrast to CD4(+)CD25(+)Foxp3(+) T cells, intrathymic development of CD8(+)CD44(high)CD122(+) Treg cells is unaffected by the RasGRP1(-/-) mutation. Moreover, RasGRP1(-/-) mice contained greater numbers of CD8(+)CD44(high)CD122(+) T cells in the spleen, relative to wild-type mice. Activated CD8 Treg cells from RasGRP1(-/-) mice retained their ability to synthesize IL-10 and suppress the proliferation of wild-type CD8(+)CD122(-) T cells, albeit at a much lower efficiency than wild-type CD8 Treg cells.     

A self-reactive TCR drives the development of Foxp3+ regulatory T cells that prevent autoimmune disease

Although Foxp3(+) regulatory T cells (Tregs) are thought to express autoreactive TCRs, it is not clear how individual TCRs influence Treg development, phenotype, and function in vivo. We have generated TCR transgenic mice (termed SFZ70 mice) using Tcra and Tcrb genes cloned from an autoreactive CD4(+) T cell isolated from a Treg-deficient scurfy mouse. The SFZ70 TCR recognizes a cutaneous autoantigen and drives development of both conventional CD4(+) Foxp3(-) T cells (T(conv)) and Foxp3(+) Tregs. SFZ70 Tregs display an activated phenotype evidenced by robust proliferation and expression of skin-homing molecules such as CD103 and P-selectin ligand. Analysis of Foxp3-deficient SFZ70 mice demonstrates that Tregs inhibit T(conv) cell expression of tissue-homing receptors and their production of proinflammatory cytokines. In addition, Treg suppression of SFZ70 T(conv) cells can be overcome by nonspecific activation of APCs. These results provide new insights into the differentiation and function of tissue-specific Tregs in vivo and provide a tractable system for analyzing the molecular requirements of Treg-mediated tolerance toward a cutaneous autoantigen.     

B cell depletion enhances T regulatory cell activity essential in the suppression of arthritis

The efficacy of B cell-depletion therapy in rheumatoid arthritis has driven interest in understanding the mechanism. Because the decrease in autoantibodies in rheumatoid arthritis does not necessarily correlate with clinical outcome, other mechanisms may be operative. We previously reported that in proteoglycan-induced arthritis (PGIA), B cell-depletion inhibits autoreactive T cell responses. Recent studies in B cell-depletion therapy also indicate a role for B cells in suppressing regulatory mechanisms. In this study, we demonstrate that B cells inhibited both the expansion and function of T regulatory (Treg) cells in PGIA. Using an anti-CD20 mAb, we depleted B cells from mice with PGIA and assessed the Treg cell population. Compared to control Ab-treated mice, Treg cell percentages were elevated in B cell-depleted mice, with a higher proportion of CD4(+) T cells expressing Foxp3 and CD25. On a per-cell basis, CD4(+)CD25(+) cells from B cell-depleted mice expressed increased amounts of Foxp3 and were significantly more suppressive than those from control Ab-treated mice. The depletion of Treg cells with an anti-CD25 mAb concurrent with B cell-depletion therapy restored the severity of PGIA to levels equal to untreated mice. Although titers of autoantibodies did not recover to untreated levels, CD4(+) T cell recall responses to the immunizing Ag returned as measured by T cell proliferation and cytokine production. Thus, B cells have the capacity to regulate inflammatory responses by enhancing effector T cells along with suppressing Treg cells.     

The influence of excessive IL-6 production in vivo on the development and function of Foxp3+ regulatory T cells

IL-6 is a proinflammatory cytokine and its overproduction is implicated in a variety of inflammatory disorders. Recent in vitro analyses suggest that IL-6 is a key cytokine that determines the balance between Foxp3(+) regulatory T cells (Tregs) and Th17 cells. However, it remains unclear whether excessive IL-6 production in vivo alters the development and function of Foxp3(+) Tregs. In this study, we analyzed IL-6 transgenic (Tg) mice in which serum IL-6 levels are constitutively elevated. Interestingly, in IL-6 Tg mice, whereas peripheral lymphoid organs were enlarged, and T cells exhibited activated phenotype, Tregs were not reduced but rather increased compared with wild-type mice. In addition, Tregs from Tg mice normally suppressed proliferation of naive T cells in vitro. Furthermore, Tregs cotransferred with naive CD4 T cells into SCID-IL-6 Tg mice inhibited colitis as successfully as those transferred into control SCID mice. These results indicate that overproduction of IL-6 does not inhibit development or function of Foxp3(+) Tregs in vivo. However, when naive CD4 T cells alone were transferred, Foxp3(+) Tregs retrieved from SCID-IL-6 Tg mice were reduced compared with SCID mice. Moreover, the Helios(-) subpopulation of Foxp3(+) Tregs, recently defined as extrathymic Tregs, was significantly reduced in IL-6 Tg mice compared with wild-type mice. Collectively, these results suggest that IL-6 overproduced in vivo inhibits inducible Treg generation from naive T cells, but does not affect the development and function of natural Tregs.     

A function for IL-7R for CD4+CD25+Foxp3+ T regulatory cells

The IL-2/IL-2R interaction is important for development and peripheral homeostasis of T regulatory (Treg) cells. IL-2- and IL-2R-deficient mice are not completely devoid of Foxp3+ cells, but rather lack population of mature CD4+CD25+Foxp3high Treg cells and contain few immature CD4+CD25-Foxp3low T cells. Interestingly, common gamma chain (gammac) knockout mice have been shown to have a near complete absence of Foxp3+ Treg cells, including the immature CD25-Foxp3low subset. Therefore, other gammac-cytokine(s) must be critically important during thymic development of CD4+CD25+Foxp3+ Treg cells apart from the IL-2. The present study was undertaken to determine whether the gammac-cytokines IL-7 or IL-15 normally contribute to expression of Foxp3 and Treg cell production. These studies revealed that mice double deficient in IL-2Rbeta and IL-7Ralpha contained a striking lack in the CD4+Foxp3+ population and the Treg cell defect recapitulated the gammac knockout mice. In the absence of IL-7R signaling, IL-15/IL-15R interaction is dispensable for the production of CD4+CD25+Foxp3+ Treg cells, indicating that normal thymic Treg cell production likely depends on signaling through both IL-2 and IL-7 receptors. Selective thymic reconstitution of IL-2Rbeta in mice double deficient in IL-2Rbeta and IL-7Ralpha established that IL-2Rbeta is dominant and sufficient to restore production of Treg cells. Furthermore, the survival of peripheral CD4+Foxp3low cells in IL-2Rbeta-/- mice appears to depend upon IL-7R signaling. Collectively, these data indicate that IL-7R signaling contributes to Treg cell development and peripheral homeostasis.     

Development of inflammatory bowel disease in Long-Evans Cinnamon rats based on CD4+CD25+Foxp3+ regulatory T cell dysfunction

A mutant strain with defective thymic selection of the Long-Evans Cinnamon (LEC) rat was found to spontaneously develop inflammatory bowel disease (IBD)-like colitis. The secretion of Th1-type cytokines including IFN-gamma and IL-2 from T cells of mesenteric lymph node cells (MLNs) and lamina propria mononuclear cells, but not spleen cells, in LEC rats was significantly increased more than that of the control Long-Evans Agouti rats through up-regulated expression of T-bet and phosphorylation of STAT-1 leading to NF-kappaB activation. In addition, the number of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells of the thymus, MLNs, and lamina propria mononuclear cells from LEC rats was significantly reduced, comparing with that of the control rats. Moreover, bone marrow cell transfer from LEC rats into irradiated control rats revealed significantly reduced CD25(+)Foxp3(+) Treg cells in thymus, spleen, and MLNs compared with those from control rats. Indeed, adoptive transfer with T cells of MLNs, not spleen cells, from LEC rats into SCID mice resulted in the development of inflammatory lesions resembling the IBD-like lesions observed in LEC rats. These results indicate that the dysfunction of the regulatory system controlled by Treg cells may play a crucial role in the development of IBD-like lesions through up-regulated T-bet, STAT-1, and NF-kappaB activation of peripheral T cells in LEC rats.     

Depletion of Foxp3+ regulatory T cells increases severity of mechanical allodynia and significantly alters systemic cytokine levels following peripheral nerve injury

Neuropathic pain is a debilitating condition caused by damage to the somatosensory nervous system, such as peripheral nerve injury. The immune system, and in particular the adaptive T cell response, plays a key role in mediating such pain. Regulatory T (Treg) cells are a small subpopulation of inhibitory T cells that prevent autoimmunity, limit immunopathology and maintain immune homeostasis. Here, we investigated the effects of conditional depletion of Treg cells on mechanical allodynia and serum cytokines in mice with chronic constriction injury (CCI) of the sciatic nerve, an animal model of neuropathic pain. We demonstrate that CCI induced the infiltration of small numbers of Treg cells within effected neuronal tissue. Utilising the transgenic DEREG (DEpletion of REGulatory T cells) mice, we confirmed effective depletion of Foxp3+ Treg cells by diphtheria toxin injections. Following CCI we observed a transient, though significant, increase in pain hypersensitivity for Treg-depleted DEREG mice compared to non-Treg-depleted mice. Analysis of systemic cytokine levels demonstrated significant changes in serum cytokine expression profiles. In particular, we observed significant increases in systemic concentration of RANTES, IL-2 and IL-5, and significant decreases in IL-12 and IFN-γ in nerve-injured Treg-depleted DEREG mice. Further analysis indicated a substantial increase in the serum concentration of IL-12p40 as a direct result of Treg cell depletion. These results suggest that depletion of Foxp3+ Treg cells promote nerve injury-induced pain hypersensitivity, partially by inducing altered systemic concentrations of cytokines, which may act to regulate neuropathic pain.     

Selective expansion of foxp3-positive regulatory T cells and immunosuppression by suppressors of cytokine signaling 3-deficient dendritic cells

Dendritic cells (DCs) induce immunity and immunological tolerance as APCs. It has been shown that DCs secreting IL-10 induce IL-10(+) Tr1-type regulatory T (Treg) cells, whereas Foxp3-positive Treg cells are expanded from naive CD4(+) T cells by coculturing with mature DCs. However, the regulatory mechanism of expansion of Foxp3(+) Treg cells by DCs has not been clarified. In this study, we demonstrated that suppressors of cytokine signaling (SOCS)-3-deficient DCs have a strong potential as Foxp3(+) T cell-inducing tolerogenic DCs. SOCS3(-/-) DCs expressed lower levels of class II MHC, CD40, CD86, and IL-12 than wild-type (WT)-DCs both in vitro and in vivo, and showed constitutive activation of STAT3. Foxp3(-) effector T cells were predominantly expanded by the priming with WT-DCs, whereas Foxp3(+) Treg cells were selectively expanded by SOCS3(-/-) DCs. Adoptive transfer of SOCS3(-/-) DCs reduced the severity of experimental autoimmune encephalomyelitis. Foxp3(+) T cell expansion was blocked by anti-TGF-beta Ab, and SOCS3(-/-) DCs produced higher levels of TGF-beta than WT-DCs, suggesting that TGF-beta plays an essential role in the expansion of Foxp3(+) Treg cells. These results indicate an important role of SOCS3 in determining on immunity or tolerance by DCs.     

IL-2, -7, and -15, but not thymic stromal lymphopoeitin, redundantly govern CD4+Foxp3+ regulatory T cell development

Common gamma chain (gammac)-receptor dependent cytokines are required for regulatory T cell (Treg) development as gammac(-/-) mice lack Tregs. However, it is unclear which gammac-dependent cytokines are involved in this process. Furthermore, thymic stromal lymphopoietin (TSLP) has also been suggested to play a role in Treg development. In this study, we demonstrate that developing CD4(+)Foxp3(+) Tregs in the thymus express the IL-2Rbeta, IL-4Ralpha, IL-7Ralpha, IL-15Ralpha, and IL-21Ralpha chains, but not the IL9Ralpha or TSLPRalpha chains. Moreover, only IL-2, and to a much lesser degree IL-7 and IL-15, were capable of transducing signals in CD4(+)Foxp3(+) Tregs as determined by monitoring STAT5 phosphorylation. Likewise, IL-2, IL-7, and IL-15, but not TSLP, were capable of inducing the conversion of CD4(+)CD25(+)Foxp3(-) thymic Treg progenitors into CD4(+)Foxp3(+) mature Tregs in vitro. To examine this issue in more detail, we generated IL-2Rbeta(-/-) x IL-7Ralpha(-/-) and IL-2Rbeta(-/-) x IL-4Ralpha(-/-) mice. We found that IL-2Rbeta(-/-) x IL-7Ralpha(-/-) mice were devoid of Tregs thereby recapitulating the phenotype observed in gammac(-/-) mice; in contrast, the phenotype observed in IL-2Rbeta(-/-) x IL-4Ralpha(-/-) mice was comparable to that seen in IL-2Rbeta(-/-) mice. Finally, we observed that Tregs from both IL-2(-/-) and IL-2Rbeta(-/-) mice show elevated expression of IL-7Ralpha and IL-15Ralpha chains. Addition of IL-2 to Tregs from IL-2(-/-) mice led to rapid down-regulation of these receptors. Taken together, our results demonstrate that IL-2 plays the predominant role in Treg development, but that in its absence the IL-7Ralpha and IL-15Ralpha chains are up-regulated and allow for IL-7 and IL-15 to partially compensate for loss of IL-2.     

Retinoic acid attenuates rheumatoid inflammation in mice

Retinoic acid is the active vitamin A derivative and is well-known to have diverse immunomodulatory actions. In this study, we investigated the impact of all-trans retinoic acid (ATRA), a biologic key metabolite of vitamin A, on the development of arthritis and the pathophysiologic mechanisms by which ATRA might have antiarthritic effects in animal model of rheumatoid arthritis (RA; collagen-induced arthritis [CIA] in DBA/1J mice). We showed that treatment with ATRA markedly suppressed the clinical and histologic signs of arthritis in the CIA mice. It reduced the expression of IL-17 in the arthritic joints. Interestingly, Foxp3(+) regulatory T cells were markedly increased and IL-17-producing CD4(+) T cells (Th17 cells) were decreased in the spleens of ATRA-treated mice. In vitro treatment with ATRA induced the expression of Foxp3 and repressed the IL-17 expression in the CD4(+) T cells in mice. ATRA suppressed the production of total IgG and IgG2a in splenocytes that were stimulated by LPS. It also reduced serum levels of total IgG and IgG2 anti-collagen Abs and germinal center formation in CIA mice. In addition, the ATRA-treated mice showed decreased osteoclast formation in arthritic joints. Moreover, ATRA downregulated the expression of receptor activator of NF-κB ligand, the leading player of osteoclastogenesis, in the CD4(+) T cells and fibroblast-like synoviocytes from patients with RA. Furthermore, ATRA prevented both human monocytes and mice bone marrow-derived monocytes/macrophage cells from differentiating into osteoclasts. These data suggest ATRA might be an effective treatment modality for RA patients.     

An instructive role of donor macrophages in mixed chimeras in the induction of recipient CD4(+)Foxp3(+) Treg cells

The immune regulatory function of macrophages (M?s) in mixed chimeras has not been determined. In the present study, with a multi-lineage B6-to-BALB/c mixed chimeric model, we examined the ability of donor-derived splenic M?s in the induction of regulatory T cells (Treg). B6 splenic M?s from mixed chimeras induced significantly less cell proliferation, more IL-10 and TGF-β, and less IL-2 and IFN-γ productions of CD4(+) T cells from BALB/c mice than naive B6 M?s did, whereas they showed similar stimulatory activity to the third part C3H CD4(+) T cells. Importantly, highly purified donor F4/80(+)CD11c(-) M?s efficiently induced recipient CD4(+)Foxp3(+) Treg cells from CD4(+)CD25(-)Foxp3(-) T cells. Furthermore, donor M?s of mixed chimeras produced more IL-10 and less IFN-γ than those of naive mice when cultured with BALB/c but not the third party C3H CD4(+) T cells. Induction of recipient CD4(+) Treg cells by donor M?s was significantly blocked by anti-IL-10, but not by anti-TGF-β mAb. Therefore, donor M?s have the ability to induce recipient CD4(+)Foxp3(+) Treg cells in a donor antigen-specific manner, at least partially, via an IL-10-dependent pathway. This study for the first time showed that, in mixed allogeneic chimeras, donor M?s could be specifically tolerant to recipients and gained the ability to induce recipient but not the third party Foxp3(+) Treg cells. Whether this approach is involved in transplant immune tolerance needs to be determined.     

Mice lacking endogenous IL-10-producing regulatory B cells develop exacerbated disease and present with an increased frequency of Th1/Th17 but a decrease in regulatory T cells

IL-10-producing B cells, also known as regulatory B cells (Bregs), play a key role in controlling autoimmunity. In this study, we report that chimeric mice specifically lacking IL-10-producing B cells (IL-10(-/-)B cell) developed an exacerbated arthritis compared with chimeric wild-type (WT) B cell mice. A significant decrease in the absolute numbers of Foxp3 regulatory T cells (Tregs), in their expression level of Foxp3, and a marked increase in inflammatory Th1 and Th17 cells were detected in IL-10(-/-) B cell mice compared with WT B cell mice. Reconstitution of arthritic B cell deficient (μMT) mice with different B cell subsets revealed that the ability to modulate Treg frequencies in vivo is exclusively restricted to transitional 2 marginal zone precursor Bregs. Moreover, transfer of WT transitional 2 marginal zone precursor Bregs to arthritic IL-10(-/-) mice increased Foxp3(+) Tregs and reduced Th1 and Th17 cell frequencies to levels measured in arthritic WT mice and inhibited inflammation. In vitro, IL-10(+/+) B cells established longer contact times with arthritogenic CD4(+)CD25(-) T cells compared with IL-10(-/-) B cells in response to Ag stimulation, and using the same culture conditions, we observed upregulation of Foxp3 on CD4(+) T cells. Thus, IL-10-producing B cells restrain inflammation by promoting differentiation of immunoregulatory over proinflammatory T cells.