Background/Purpose: During the T cell differentiation, signal transducer and activators of transcription (STAT) family transcription factors play pivotal roles in specifying T cell lineages. T follicular helper (Tfh) cells serve important roles in the development and progression of systemic lupus erythematosus (SLE). To assess the characteristics and mechanisms of differentiation of Tfh cells, we studied the underlying epigenetic modifications by cytokine-induced STAT activation and the phenotype of circulating T helper cells in SLE patients.

Methods: Peripheral blood mononuclear cells from patients with SLE and healthy controls (HC) were analyzed by flow cytometry. The phenotype of circulating T cells was defined based on flow cytometric analysis for human immune system termed “the Human Immunology Project” proposed by NIH/FOCIS. Naive CD4⁺ T cells and memory CD4⁺ T cells were isolated and cultured with T cell receptor (TCR) and various cytokines in vitro. Expression of characteristic markers of Tfh cells and phosphorylation of STATs were analyzed by flow cytometry and qPCR. Histone modifications were evaluated by chromatin immunoprecipitation (ChIP)-PCR. Peripheral blood mononuclear cells from SLE patients and healthy controls were analyzed by flow cytometry and productions of cytokines in serum were tested by cytometric bead array.

Results: Among the immunoregulatory cytokines, IL-12 induced the differentiation of CD4⁺CXCR5⁺CXCR3⁺Bcl-6⁺T-bet⁺IL-21⁺IFN-γ⁺ T cells, which share features of both Tfh and Th1 cells. The loci of Bcl-6 and T-bet at STAT binding sites were marked by bivalent histone modifications. After IL-12-stimulation, both STAT1 and STAT4 were phosphorylated simultaneously and directly bound on BCL6 (encoding Bcl-6) and TBX21 (encoding T-bet) gene loci accompanied by suppression of repressive histone mark trimethylated histone 3 lysine 27. Compared with HCs, the proportion of CD4⁺CXCR5⁺CXCR3⁺CCR6^–CD69⁺ activated Tfh-Th1-like cells were significantly increased in patients with SLE (mean 0.7 vs 0.4, p=0.02). Levels of serum IL-12 and expression of IL-12 receptors in memory T cells were significantly increased in patients with SLE compared to HCs (p<0.01). Furthermore, the level of pSTAT1, pSTAT4 and T-bet were higher in activated Tfh-Th1-like cells than non-Tfh-Th1 cells (p<0.05).

Conclusion: The findings suggest that IL-12-mediated co-activation of STAT1 and STAT4 alters histone modification, resulting in development of Tfh-Th1-like cells that are characteristically expanded in patients with SLE. This could be one of underlying mechanisms responsible for the pathogenesis of Tfh cells in SLE. Thus, modulation of STAT-mediated gene regulation in Tfh cells potentially offer the opportunities for cell-specific treatment of SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/activation-of-t-follicular-helper-cells-through-epigenetic-regulation-by-stat1-and-stat4-in-lupus-patients/