Keeping autoimmunity in check: how to control a Th17 cell controller

Differential Roles of the mTOR-STAT3 Signaling in Dermal γδ T Cell Effector Function in Skin Inflammation

Dermal γδT cells play critical roles in skin homeostasis and inflammation. However, the underlying molecular mechanisms by which these cells are activated have not been fully understood. Here, we show that the mechanistic or mammalian target of rapamycin (mTOR) and STAT3 pathways are activated in dermal γδT cells in response to innate stimuli such as interleukin-1β (IL-1β) and IL-23. Although both mTOR complex 1 (mTORC1) and mTORC2 are essential for dermal γδT cell proliferation, mTORC2 deficiency leads to decreased dermal γδT17 cells. It appears that mitochondria-mediated oxidative phosphorylation is critical in this process. Notably, although the STAT3 pathway is critical for dermal Vγ4T17 effector function, it is not required for γδ6T17 cells. Transcription factor IRF-4 activation promotes dermal γδT cell IL-17 production by linking IL-1β and IL-23 signaling. The absence of mTORC2 in dermal γδT cells, but not STAT3, ameliorates skin inflammation. Taken together, our results demonstrate that the mTOR-STAT3 signaling differentially regulates dermal γδT cell effector function in skin inflammation.

Cai et al. demonstrate that the mTOR and STAT3 signaling pathways differentially regulate dermal Vγ4 and Vγ6 T cell effector function, leading to distinct outcomes in skin inflammation.

Loss and dysregulation of Th17 cells during HIV infection

Bacterial translocation across the damaged mucosal epithelium has emerged as a major paradigm for chronic immune activation observed during HIV infection. T helper 17 (Th17) cells are a unique lineage of T helper cells that are enriched in mucosal tissues and are thought to play a central role in protecting the integrity of the mucosal barrier and maintaining immune homeostasis at mucosal sites. Th17 cells are lost very early during the course of HIV infection, and their loss has been shown to correlate with bacterial translocation. Interestingly, Th17 cells are unable to completely recover from the early destruction even after successful antiretroviral therapy (ART). Here, we review some of the potential mechanisms for the loss and dysregulation of Th17 cells during HIV infection.

Expression of IRF-4 and IBP in skin lesions of patients with psoriasis vulgaris

The expression of the interferon regulatory factor 4 (IRF-4) and the IRF-4-binding protein (IBP) in psoriatic skin lesions was investigated. The expression of IRF-4 and IBP in skin lesions of 20 patients with psoriasis vulgaris were immunohistochemically dectected. Normal skin from 10 healthy people was used as normal control. The study showed that expression of IRF-4 was increased significantly in keratinocytes and inflammatory cells in the lesions of psoriasis vulgaris than that in the normal control. The detection revealed that IBP expression in keratinocytes, lymphocytes, hair follicles, and sebaceous glands in normal skin was significantly lower than that in the lesions of psoriasis vulgaris (P<0.05). Both IRF-4 and IBP might be involved in the pathogenesis of psoriasis vulgaris.

Progesterone promotes differentiation of human cord blood fetal T cells into T regulatory cells but suppresses their differentiation into Th17 cells

Progesterone, a key female sex hormone with pleiotropic functions in maintenance of pregnancy, has profound effects on regulation of immune responses. We report in this work a novel function of progesterone in regulation of naive cord blood (CB) fetal T cell differentiation into key T regulatory cell (Treg) subsets. Progesterone drives allogeneic activation-induced differentiation of CB naive, but not adult peripheral blood, T cells into immune-suppressive Tregs, many of which express FoxP3. Compared with those induced in the absence of progesterone, the FoxP3(+) T cells induced in the presence of progesterone highly expressed memory T cell markers. In this regard, the Treg compartment in progesterone-rich CB is enriched with memory-type FoxP3(+) T cells. Moreover, CB APCs were more efficient than their peripheral blood counterparts in inducing FoxP3(+) T cells. Another related function of progesterone that we discovered was to suppress the differentiation of CB CD4(+) T cells into inflammation-associated Th17 cells. Progesterone enhanced activation of STAT5 in response to IL-2, whereas it decreased STAT3 activation in response to IL-6, which is in line with the selective activity of progesterone in generation of Tregs versus Th17 cells. Additionally, progesterone has a suppressive function on the expression of the IL-6 receptor by T cells. The results identified a novel role of progesterone in regulation of fetal T cell differentiation for promotion of immune tolerance.

Novel gamma-chain cytokines as candidate immune modulators in immune therapies for cancer

Cytokines that signal through the common-gamma chain are potent growth factors for T cells and natural killer cells. Interleukin (IL)-2, the gammac prototype, can mediate antitumor effects as a single agent or in the context of multimodality regimens but is limited by side effects and a propensity for expansion of regulatory T cells. IL-7, IL-15, and IL-21 each possess properties that can be exploited in the context of immunotherapy for cancer. Each has been demonstrated to mediate potent vaccine adjuvant effects in tumor models, and each can enhance the effectiveness of adoptive immunotherapies. Although the overlap among the agents is significant, IL-7 is uniquely immunorestorative and preferentially augments reactivity of naive populations, IL-15 potently augments reactivity of CD8 memory cells and natural killer cells, and IL-21 preferentially expands the inflammatory Th17 subset and may limit terminal differentiation of effector CD8 cells. Clinical trials of IL-7 and IL-21 have already been completed and, so far, demonstrate safety and biologic activity of these agents. Clinical trials of IL-15 are expected soon. Ultimately, these agents are expected to be most effective in the context of multimodal immunotherapy regimens, and careful clinical trial design will be needed to efficiently identify the proper doses, regimens, and settings in which to exploit their biologic properties for therapeutic gain.

Novel interactions of a microbial superantigen with TLR2 and TLR4 differentially regulate IL-17 and Th17-associated cytokines

Mycoplasma arthritidis, an inflammatory murine pathogen, secretes a potent superantigen, Mycoplasma arthritidis mitogen (MAM) that contributes to toxic shock, arthritis and skin necrosis. Previously we showed that MAM induced type 2 T-cell cytokines in mice that express functional TLR2 and TLR4, but type 1 cytokines in mice that lack TLR4 function. We show here that IL-17, pSTAT3 and retinoid-related orphan nuclear receptorγt are rapidly expressed in wild-type C3H/HeSnJ (TLR2+/4+) mice but are significantly delayed in mutant C3H/HeJ (TLR2+/4-) mice. This marked kinetic difference was associated with a high level of IL-6 in TLR2+/4+ mice versus high levels of IL-1β and TNFα in TLR2+/4- mice. Also antibodies to IL-6 and IL-23, suppressed IL-17 responses to MAM in TLR2+/4+ mice whereas anti-IL-1β, but not anti-TNFα, enhanced IL-17 in TLR2+/4- mice. Antibody blocking of TLR4 in TLR2+/4+ mice decreased IL-17 and IL-6 but not IL-23. In addition both IL-17 and IL-6 but not IL-23 were elevated in TLR2 KO mice versus wild-type TLR2+/4+ mice given MAM. We conclude that the MAM interaction with TLR2 versus TLR4 leads to distinct cytokine pathways mediated primarily by IL-1β or IL-6/IL-17 signalling respectively. Our findings suggest that the differential interaction of MAM with different TLRs might play an important role in disease outcomes by M. arthritidis.

Modulation of immune responses through direct activation of Toll-like receptors to T cells

Toll-like receptors (TLRs), which are a family of pattern recognition receptors (PRRs), are involved critically in the generation and regulation of innate immunity as well as initiation of subsequent adaptive immune responses. However, recent research results showed that different subsets of T cells express certain types of TLRs during development and activation stages. Importantly, TLRs participate in the direct regulation of adaptive immune response, possibly as co-stimulatory molecules. In this review we summarize recent studies about the novel regulation of TLRs on the homeostasis and immunity of different T cell subtypes including CD4+CD25+T regulatory cells (Treg) and interleukin (IL)-17-producing CD4+T cells (T helper type 17). The direct involvement of TLRs in T cell-mediated immunity prompted us to reconsider the role of TLRs in the occurrence of autoimmune diseases, infectious diseases and graft rejection. The important effects of TLRs in T cell-intrinsic components also prompt us to explore novel vaccine adjuvants for modifying desired immune responses in an efficient way.