IL-6 controls Th17 immunity in vivo by inhibiting the conversion of conventional T cells into Foxp3+ regulatory T cells

The conditions leading to the induction of adaptive Foxp3⁺ regulatory T cells (T-regs) from peripheral T cells in vivo are incompletely understood. Here, we show that unresponsiveness of T cells to IL-6 by T cell-selective deletion of gp130 or immunization of wild-type mice with antigen in incomplete Freund's adjuvant (IFA), which fails to induce IL-6, promotes the conversion of peripheral CD4⁺ T cells into adaptive Foxp3⁺ T-regs. Thus, both T cell-conditional gp130 knockout (KO) mice immunized with MOG35-55 in complete Freund's adjuvant (CFA) and wild-type mice immunized with MOG35-55 in IFA develop overwhelming antigen-specific T-reg responses and are protected from experimental autoimmune encephalomyelitis (EAE). Depletion of T-regs restores T helper (Th)17 responses and clinical EAE in MOG/CFA-immunized T cell-conditional gp130 KO mice, but not in MOG/IFA-immunized wild-type mice. We conclude that in the absence of T-regs, IL-6 signaling is dispensable for the induction of Th17 cells, and alternative pathways exist to induce Th17 cells and EAE in the absence of IL-6 signaling. However, IL-6 signaling is dominant in inhibiting the conversion of conventional T cells into Foxp3⁺ T-regs in vivo, and in the absence of IL-6 signaling, no other cytokine can substitute in inhibiting T-reg conversion. These data identify IL-6 as an important target to modulate autoimmune responses and chronic inflammation.     

Inducible Foxp3+ regulatory T-cell development by a commensal bacterium of the intestinal microbiota

To maintain intestinal health, the immune system must faithfully respond to antigens from pathogenic microbes while limiting reactions to self-molecules. The gastrointestinal tract represents a unique challenge to the immune system, as it is permanently colonized by a diverse amalgam of bacterial phylotypes producing multitudes of foreign microbial products. Evidence from human and animal studies indicates that inflammatory bowel disease results from uncontrolled inflammation to the intestinal microbiota. However, molecular mechanisms that actively promote mucosal tolerance to the microbiota remain unknown. We report herein that a prominent human commensal, Bacteroides fragilis, directs the development of Foxp3⁺ regulatory T cells (Tregs) with a unique “inducible” genetic signature. Monocolonization of germ-free animals with B. fragilis increases the suppressive capacity of Tregs and induces anti-inflammatory cytokine production exclusively from Foxp3⁺ T cells in the gut. We show that the immunomodulatory molecule, polysaccharide A (PSA), of B. fragilis mediates the conversion of CD4⁺ T cells into Foxp3⁺ Treg cells that produce IL-10 during commensal colonization. Functional Foxp3⁺ Treg cells are also produced by PSA during intestinal inflammation, and Toll-like receptor 2 signaling is required for both Treg induction and IL-10 expression. Most significantly, we show that PSA is not only able to prevent, but also cure experimental colitis in animals. Our results therefore demonstrate that B. fragilis co-opts the Treg lineage differentiation pathway in the gut to actively induce mucosal tolerance.     

Generation of regulatory dendritic cells and CD4+Foxp3+ T cells by probiotics administration suppresses immune disorders

The beneficial effects of probiotics have been described in many diseases, but the mechanism by which they modulate the immune system is poorly understood. In this study, we identified a mixture of probiotics that up-regulates CD4⁺Foxp3⁺ regulatory T cells (Tregs). Administration of the probiotics mixture induced both T-cell and B-cell hyporesponsiveness and down-regulated T helper (Th) 1, Th2, and Th17 cytokines without apoptosis induction. It also induced generation of CD4⁺Foxp3⁺ Tregs from the CD4⁺CD25⁻ population and increased the suppressor activity of naturally occurring CD4⁺CD25⁺ Tregs. Conversion of T cells into Foxp3⁺ Tregs is directly mediated by regulatory dendritic cells (rDCs) that express high levels of IL-10, TGF-β, COX-2, and indoleamine 2,3-dioxygenase. Administration of probiotics had therapeutical effects in experimental inflammatory bowel disease, atopic dermatitis, and rheumatoid arthritis. The therapeutical effect of the probiotics is associated with enrichment of CD4⁺Foxp3⁺ Tregs in the inflamed regions. Collectively, the administration of probiotics that enhance the generation of rDCs and Tregs represents an applicable treatment of inflammatory immune disorders.     

Activated rat hepatic stellate cells influence Th1/Th2 profile in vitro

AIM: To investigate the effects of activated rat hepatic stellate cells(HSCs) on rat Th1/Th2 profile in vitro.METHODS: Growth and survival of activated HSCs and CD4+ T lymphocytes cultured alone or together was assessed after 24 or 48 h. CD4+ T lymphocytes were then cultured with or without activated HSCs for 24 or 48 h and the proportion of Th1 [interferon(IFN)-γ+] and Th2 [interleukin(IL)-4+] cells was assessed by flow cytometry. Th1 and Th2 cell apoptosis was assessed after 24 h of co-culture using a caspase-3 staining procedure. Differentiation rates of Th1 and Th2 cells from CD4+ T lymphocytes that were positive for CD25 but did not express IFN-γ or IL-4 were also assessed after 48 h of co-culture with activated HSCs. Galectin-9 expression in HSCs was determined by immunofluorescence and Western blotting. ELISA was performed to assess galectin-9 secretion from activated HSCs.RESULTS: Co-culture of CD4+ T lymphocytes with activated rat HSCs for 48 h significantly reduced the proportion of Th1 cells compared to culture-alone conditions(-1.73% ± 0.71%; P 0.05), whereas the proportion of Th2 cells was not altered; the Th1/Th2 ratio was significantly decreased(-0.44 ± 0.13; P 0.05). In addition, the level of IFN-γ in Th1 cells wasdecreased(-65.71 ± 9.67; P 0.01), whereas the level of IL-4 in Th2 cells was increased(82.79 ± 25.12; P 0.05) by co-culturing, as measured by mean fluorescence intensity by flow cytometry. Apoptosis rates in Th1(12.27% ± 0.99%; P 0.01) and Th2(1.71% ± 0.185%; P 0.01) cells were increased 24 h after co-culturing with activated HSCs; the Th1 cell apoptosis rate was significantly higher than in Th2 cells(P 0.01). Galectin-9 protein expression was significantly decreased in HSCs only 24 h after coculturing(P 0.05) but not after 48 h. Co-culture for 48 h significantly increased the differentiation of Th1 and Th2 cells; however, the increase in the proportion of Th2 cells was significantly higher than that of Th1 cells(1.85% ± 0.48%; P 0.05).CONCLUSION: Activated rat HSCs lower the Th1/Th2 profile, inhibiting the Th1 response and enhancing the Th2 response, and this may be a novel pathway for liver fibrogenesis.     

Differentiation of naive human CD4+ T cells into Th2 cells: The role of prostaglandin E2

T-helper (Th) 2 cells, which produce interleukin (IL)-4, IL-5, IL-10 and IL-13 upon stimulation of their T cell receptors, play an important role in the development of human allergic diseases. However, the precise mechanism involved in the differentiation of Th2 cells is not well understood compared with that of Th1 cells. The selective differentiation of Th1 or Th2 subsets is established during priming under the influence of a variety of factors. Prostaglandin E₂ (PGE₂) is one of those factors. Prostaglandin E₂ produced by antigen presenting cells directly affects the naive CD4⁺ T cells, causing them to differentiate into Th2 cells. This effect is mediated by the elevation of cyclic adenosine monophosphate (cAMP) at the early stage of T cell activation. IL-4 and PGE₂ lead naive CD4⁺ T cells to differentiate into Th2 cells cooperatively, by distinct signal transduction. Both PGE2 and IL-4 inhibit the hypomethylation of the proximal regulatory regions of the genomic IFN-γ gene, whose hypomethylation has been suggested as being important for the IFN-γ production by CD4⁺ T cells stimulated through their antigen receptors. Prostaglandin E₂ facilitates Th2 differentiation of naive CD4⁺ T cells by acting not only on T cells directly but also on antigen presenting cells by inhibiting their IL-12 production. The production of PGE₂ by monocytes is increased significantly in allergic patients. These results, taken collectively, suggest that PGE₂ plays an important role in facilitating the differentiation of Th2 cells in vivo.     

Human Langerhans cells induce distinct IL-22-producing CD4+ T cells lacking IL-17 production

IL-22 is a cytokine that acts mainly on epithelial cells. In the skin, it mediates keratinocyte proliferation and epidermal hyperplasia and is thought to play a central role in inflammatory diseases with marked epidermal acanthosis, such as psoriasis. Although IL-22 was initially considered a Th17 cytokine, increasing evidence suggests that T helper cells can produce IL-22 even without IL-17 expression. In addition, we have shown the existence of this unique IL-22-producing T cell in normal skin and in the skin of psoriasis and atopic dermatitis patients. In the present study, we investigated the ability of cutaneous resident dendritic cells (DCs) to differentiate IL-22-producing cells. Using FACS, we isolated Langerhans cells (LCs; HLA-DR⁺CD207⁺ cells) and dermal DCs (HLA-DR^hiCD11c⁺BDCA-1⁺ cells) from normal human epidermis and dermis, respectively. Both LCs and dermal DCs significantly induced IL-22-producing CD4⁺ and CD8⁺ T cells from peripheral blood T cells and naive CD4⁺ T cells in mixed leukocyte reactions. LCs were more powerful in the induction of IL-22-producing cells than dermal DCs. Moreover, in vitro-generated LC-type DCs induced IL-22-producing cells more efficiently than monocyte-derived DCs. The induced IL-22 production was more correlated with IFN-γ than IL-17. Surprisingly, the majority of IL-22-producing cells induced by LCs and dermal DCs lacked the expression of IL-17, IFN-γ, and IL-4. Thus, LCs and dermal DCs preferentially induced helper T cells to produce only IL-22, possibly “Th22” cells. Our data indicate that cutaneous DCs, especially LCs, may control the generation of distinct IL-22 producing Th22 cells infiltrating into the skin.     

CD4+ T cell regulation of CD25 expression controls development of short-lived effector CD8+ T cells in primary and secondary responses

Both CD4⁺ T cell help and IL-2 have been postulated to “program” activated CD8⁺ T cells for memory cell development. However, the linkage between these two signals has not been well elucidated. Here we have studied effector and memory CD8⁺ T cell differentiation following infection with three pathogens (Listeria monocytogenes, vesicular stomatitis virus, and vaccinia virus) in the absence of both CD4⁺ T cells and IL-2 signaling. We found that expression of CD25 on antigen-specific CD8⁺ T cells peaked 3–4 days after initial priming and was dependent on CD4⁺ T cell help, likely through a CD28:CD80/86 mediated pathway. CD4⁺ T cell or CD25-deficiency led to normal early effector CD8⁺ T cell differentiation, but a subsequent lack of accumulation of CD8⁺ T cells resulting in overall decreased memory cell generation. Interestingly, in both primary and recall responses KLRG1^high CD127^low short-lived effector cells were drastically diminished in the absence of IL-2 signaling, although memory precursors remained intact. In contrast to previous reports, upon secondary antigen encounter CD25-deficient CD8⁺ T cells were capable of undergoing robust expansion, but short-lived effector development was again impaired. Thus, these results demonstrated that CD4⁺ T cell help and IL-2 signaling were linked via CD25 up-regulation, which controls the expansion and differentiation of antigen-specific effector CD8⁺ T cells, rather than “programming” memory cell traits.     

Regulation of memory CD4 T-cell pool size and function by natural killer T cells in vivo

To develop more effective vaccines and strategies to regulate chronic inflammatory diseases, it is important to understand the mechanisms of immunological memory. Factors regulating memory CD4⁺ T helper (Th)-cell pool size and function remain unclear, however. We show that activation of type I invariant natural killer T (iNKT) cells with glycolipid ligands and activation of type II natural killer T (NKT) cells with the endogenous ligand sulfatide induced dramatic proliferation and expansion of memory, but not naïve, CD4 T cells. NKT cell-induced proliferation of memory Th1 and Th2 cells was dependent largely on the production of IL-2, with Th2-cell proliferation also affected by loss of IL-4. Type II NKT cells were also required for efficient maintenance of memory CD4 T cells in vivo. Activation of iNKT cells resulted in up-regulation of IFN-γ expression by memory Th2 cells. These IFN-γ–producing memory Th2 cells showed a decreased capability to induce Th2 cytokines and eosinophilic airway inflammation. Thus, activated NKT cells directly regulate memory CD4 T-cell pool size and function via the production of cytokines in vivo.     

CD4 cell-secreted, posttranslationally modified cytokine GIF suppresses Th2 responses by inhibiting the initiation of IL-4 production

T helper 2 (Th2) cells are critical to the induction of IgE antibody and allergic inflammation, but how the pathological pathways are controlled in nonallergic individuals remains unclear. Here we report that glycosylation-inhibiting factor (GIF) suppresses Th2 effector generation. GIF is a cytokine encoded by the same gene that codes for macrophage migration inhibitory factor (MIF). GIF-deficient mice demonstrated enhanced T-dependent antibody formation especially of IgE isotype and allergic airway inflammation with the generation of regulatory T cells unaffected. GIF-deficient macrophages and dendritic cells revealed normal responsiveness to toll-like receptor (TLR) ligands. GIF undergoes a unique posttranslational modification, cysteinylation. The modified GIF, mainly secreted by activated T cells derived from CD4⁺CD25⁻ cells, inhibited IL-4 production by the same cells whereas the unmodified GIF showed no effect. Bone marrow chimera experiment demonstrated that T cell-derived GIF suppressed the generation of Th effectors that secrete IL-4. During the first 24 h of CD3/CD28 stimulation in vitro, GIF secreted from naïve CD4 cells acted on the same cells, maintained nuclear factor of activated T cells (NFAT)c2 in the nucleus, and repressed IL-4 mRNA levels. Thus, GIF represents a self-regulatory mechanism of Th2 cell generation from naïve CD4 cells, in which the posttranslational modification plays a crucial role.     

Optimal induction of T helper 17 cells in humans requires T cell receptor ligation in the context of Toll-like receptor-activated monocytes

Recently, a new lineage of CD4⁺ T cells has been described in the mouse that specifically secretes IL-17 [T helper (Th) 17]. This discovery has led to a revision of the hypothesis that many autoimmune diseases are predominantly a Th1 phenomenon and may instead be critically dependent on the presence of Th17 cells. Murine Th17 cells differentiate from naïve T cell precursors in the presence of TGF-β and IL-6 or IL-21. However, given their putative importance in human autoimmunity, very little is known about the pathways that control the expression of IL-17 in humans. Here we show that the factors that determine the expression of IL-17 in human CD4⁺ T cells are completely different from mice. IL-6 and IL-21 were unable to induce IL-17 expression in either naïve or effector T cells, and TGF-β actually inhibited IL-17 expression. The expression of IL-17 was maximally induced from precommitted precursors present in human peripheral blood by cell–cell contact with Toll-like receptor-activated monocytes in the context of T cell receptor ligation. Furthermore, unlike IFN-γ, IL-17 expression was not suppressed by the presence of FOXP3⁺ regulatory CD4⁺ T cells. Taken together, these data indicate that human and mouse Th17 cells have important biological differences that may be of critical importance in the development of therapeutic interventions in diseases characterized by aberrant T cell polarization.