A distinct GM-CSF ⁺ T helper cell subset requires T-bet to adopt a T _H 1 phenotype and promote neuroinflammation

Abstract

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.

Single-cell immune profiling reveals a developmentally distinct CD4+ GM-CSF+ T-cell lineage that induces GI tract GVHD

“…22 A frequent observation in human studies and murine inflammatory disease models, including GVHD, has been the identification of heterogeneous populations of CD4 + GM-CSF + T cells in tissue culture and in vivo within specific target tissues; specifically, those that make GM-CSF alone or cells that produce GM-CSF in conjunction with other T H -defining cytokines, most often IFN- or IL-17. 6,7,[23][24][25][26] This finding has raised the question as to whether these cells constitute a subset of T H 1 and/or T H 17 cells, or if there exists a distinct T H GM-CSF subset within this heterogenous population that differentiate these cells ontologically from more classically defined T H 1 and T H 17 cells. 27 To date, however, characterization of CD4 + GM-CSF + T cell heterogeneity within specific tissue sites in inflammatory diseases such as GVHD has not been addressed.…”

IFN-β Acts on Monocytes to Ameliorate CNS Autoimmunity by Inhibiting Proinflammatory Cross-Talk Between Monocytes and Th Cells

“…Our results confirmed that IL-1b signaling is not necessary for Th17 development, but rather for GM-CSF expression by Th cells. Even though IL-1b has a strong GM-CSF-inducing effect, GM-CSF expression by Th cells was not abrogated without IL-1b signaling, indicating that other cytokines, such as IL-2, IL-7, and IL-23 (28), also induce GM-CSF expression. The relationship between IL-1b and GM-CSF is reciprocal, as GM-CSF induces IL-1b expression in myeloid cells and the lack of GM-CSF drastically reduces IL-1b expression by monocytes in the CNS of mice with EAE.…”

“…We show that in the CNS of mice with EAE, rIFN-b treatment induces similar monocyte subset with pDC-like phenotype, expressing IFN-b, type-I IFN-related genes, PDCA-1, and Siglec-H. pDCs are known as the major source of IFN-b, but monocytes/macrophages can also produce IFN-b during viral infections and in EAE (53)(54)(55)(56). Given that pDCs have an (45), was initially associated with the development of Th17 cells (61), but more recent studies emphasize its role in promoting GM-CSF expression by Th cells (26,28). Our results confirmed that IL-1b signaling is not necessary for Th17 development, but rather for GM-CSF expression by Th cells.…”

“…rIFN-b abrogated IL-1b production in co-cultures of naïve CD4 + T cells and APCs by acting on APCs (Supplementary Figure 5D). Given that IL-1b induces GM-CSF expression in Th cells (26,28), we hypothesized that rIFN-b suppresses their GM-CSF expression by inhibiting IL-1b expression by APCs. We confirmed that IL-1b induces GM-CSF production by Th cells in vitro, in a dose-dependent manner (Supplementary Figures 5E, F).…”

“…Although different subsets of myeloid cells express the receptor, only expression by monocytes is necessary for EAE to develop (6). Th cells are the relevant source of GM-CSF in EAE, and their encephalitogenicity depends on the capacity to produce GM-CSF (26)(27)(28). Recent studies have shown increased frequencies of GM-CSF + Th cells in the periphery and cerebrospinal fluid (CSF) of MS patients compared to healthy individuals, and treatments with some immunomodulatory therapies, such as rIFN-b, normalize their numbers (29)(30)(31)(32).…”