Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). Studies in animal models of MS have shown that granulocyte-macrophage colony-stimulating factor (GM-CSF) produced by T cells is necessary for development of autoimmune CNS inflammation. This suggests that GM-CSF may have a pathogenic role in MS as well, and a clinical trial testing its blockade is ongoing. However, there have been few reports on GM-CSF production by T cells in MS. The objective of this study was to characterize GM-CSF production by T cells of MS patients, and to determine the effect of interferon-beta (IFN-β) therapy on its production. GM-CSF production by peripheral blood (PB) T cells and the effects of IFN-β were characterized in samples of untreated and IFN-β-treated MS patients vs. healthy subjects. GM-CSF production by T cells in MS brain lesions was analyzed by immunofluorescence. Untreated MS patients had significantly greater numbers of GM-CSF+ CD4+ and CD8+ T cells in PB compared to healthy controls and IFN-β-treated MS patients. IFN-β significantly suppressed GM-CSF production by T cells in vitro. A number of CD4+ and CD8+ T cells in MS brain lesions expressed GM-CSF. Elevated GM-CSF production by PB T cells in MS is indicative of aberrant hyperactivation of the immune system. Given its essential role in animal models, abundant GM-CSF production at the sites of CNS inflammation suggests that GM-CSF contributes to MS pathogenesis. Our findings also reveal a potential mechanism of IFN-β therapy, namely suppression of GM-CSF production.

Peripheral tolerance to autoantigens is induced via suppression of self-reactive lymphocytes, stimulation of tolerogenic dendritic cells (DCs) and regulatory T (Treg) cells. Interleukin (IL)-27 induces tolerogenic DCs and Treg cells; however, it is not known whether IL-27 is important for tolerance induction. We immunized wild-type (WT) and IL-27 receptor (WSX-1) knockout mice with MOG 35–55 for induction of experimental autoimmune encephalomyelitis and intravenously (i.v.) injected them with MOG 35–55 after onset of disease to induce i.v. tolerance. i.v. administration of MOG 35–55 reduced disease severity in WT mice, but was ineffective in Wsx −/− mice. IL-27 signaling in DCs was important for tolerance induction, whereas its signaling in T cells was not. Further mechanistic studies showed that IL-27-dependent tolerance relied on cooperation of distinct subsets of spleen DCs with the ability to induce T cell-derived IL-10 and IFN-γ. Overall, our data show that IL-27 is a key cytokine in antigen-induced peripheral tolerance and may provide basis for improvement of antigen-specific tolerance approaches in multiple sclerosis and other autoimmune diseases.

Elevation of granulocyte-macrophage colony-stimulating factor (GM-CSF)–producing T helper (TH) cells has been associated with several autoimmune diseases, suggesting a potential role in the pathogenesis of autoimmunity. However, the identity of GM-CSF–producing TH cells has not been closely examined. Using single-cell RNA sequencing and high-dimensional single-cell mass cytometry, we identified eight populations of antigen-experienced CD45RA−CD4+ T cells in blood of healthy individuals including a population of GM-CSF–producing cells, known as THGM, that lacked expression of signature transcription factors and cytokines of established TH lineages. Using GM-CSF-reporter/fate reporter mice, we show that THGM cells are present in the periphery and central nervous system in a mouse model of experimental autoimmune encephalomyelitis. In addition to GM-CSF, human and mouse THGM cells also expressed IL-2, tumor necrosis factor (TNF), IL-3, and CCL20. THGM cells maintained their phenotype through several cycles of activation but up-regulated expression of T-bet and interferon-γ (IFN-γ) upon exposure to IL-12 in vitro and in the central nervous system of mice with autoimmune neuroinflammation. Although T-bet was not required for the development of THGM cells, it was essential for their encephalitogenicity. These findings demonstrate that THGM cells constitute a distinct population of TH cells with lineage characteristics that are poised to adopt a TH1 phenotype and promote neuroinflammation.

Summary Tumour pathogenesis is characterized by an immunosuppressive microenvironment that limits the development of effective tumour‐specific immune responses. This is in part the result of tumour‐dependent recruitment and activation of regulatory cells, such as myeloid‐derived suppressor cells and regulatory T cells in the tumour microenvironment and draining lymph nodes. Shedding of gangliosides by tumour cells has immunomodulatory properties, suggesting that gangliosides may be a critical factor in initiating an immunosuppressive microenvironment. To better define the immunomodulatory properties of gangliosides on antigen‐specific T‐cell activation and development we have developed an in vitro system using ganglioside‐treated murine bone‐marrow‐derived dendritic cells to prime and activate antigen‐specific CD4+ T cells from AND T‐cell receptor transgenic mice. Using this system, ganglioside treatment promotes the development of a dendritic cell population characterized by decreased CD86 (B7‐2) expression, and decreased interleukin‐12 and interleukin‐6 production. When these cells are used as antigen‐presenting cells, CD4 T cells are primed to proliferate normally, but have a defect in T helper (Th) effector cell development. This defect in Th effector cell responses is associated with the development of regulatory T‐cell activity that can suppress the activation of previously primed Th effector cells in a contact‐dependent manner. In total, these data suggest that ganglioside‐exposed dendritic cells promote regulatory T‐cell activity that may have long‐lasting effects on the development of tumour‐specific immune responses.