Objective. This study was undertaken to identify characteristics of follicular regulatory T (Tfr) cells and elucidate the mechanisms by which follicular helper T (Tfh) cells convert to Tfr cells. We probed the phenotype of T helper cells in patients with systemic lupus erythematosus (SLE) and underlying transcriptional regulation using cytokine-induced STAT family factors. Methods. Peripheral blood mononuclear cells from 41 patients with SLE and 26 healthy donors were used to sort out the memory Tfh cell subset, and Tfh cells were cultured under various conditions. The phenotype of T helper cells and underlying mechanisms of transcriptional regulation were probed using flow cytometry and quantitative polymerase chain reaction analyses. These analyses evaluated the expression of characteristic markers and phosphorylation of STATs. Chromatin immunoprecipitation was used to evaluate histone modifications. Results. In patients with SLE, the proportion of CD4+CXCR5+FoxP3-PD-1 high Tfh cells was increased (P < 0.01), whereas the proportion of CD4+CXCR5+CD45RA-FoxP3 high activated Tfr cells was decreased (P < 0.05). Serum interleukin-2 (IL-2) levels were also reduced in patients with SLE. IL-2 induced conversion of memory Tfh cells to functional Tfr cells, which was characterized by CXCR5+Bcl-6+FoxP3 high pSTAT3+pSTAT5+ cells. The loci of FOXP3 and BCL6 at STAT binding sites were marked by bivalent histone modifications. Following IL-2 stimulation, STAT3 and STAT5 selectively bound to FOXP3 and BCL6 gene loci accompanied by suppression of H3K27me3. Finally, IL-2 stimulation suppressed the generation of CD38+CD27 high plasmablasts in Tfh and B cell coculture assays ex vivo. Conclusion. Impaired function of Tfr cells might be attributed to defective IL-2 production. Exogenous IL-2 restores the function of Tfr cells through the conversion of Tfh cells to Tfr cells in patients with SLE. Thus, restoring balance between Tfh and Tfr cells may provide new therapeutic approaches in SLE.
Our findings suggest that IL-12-mediated co-activation of STAT1 and STAT4 alters histone modification, resulting in differentiation of Tfh-Th1-like cells that are characteristically expanded in patients with SLE. This could be one of the underlying mechanisms responsible for expansion of Tfh-Th1-like cells and potentially helpful towards development of cell-specific treatment for SLE.
B cells play a crucial role in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE). However, the relevance of the metabolic pathway in the differentiation of human B cell subsets remains unknown. In this article, we show that the combination of CpG/TLR9 and IFN-α markedly induced the differentiation of CD27IgD unswitched memory B cells into CD27CD38 plasmablasts. The response was accompanied by mammalian target of rapamycin complex 1 (mTORC1) activation and increased lactate production, indicating a shift to glycolysis. However, CpG alone induced the differentiation of unswitched memory B cells into CD27IgD memory B cells with high cytokine production, but such differentiation was suppressed by IFN-α. AMP-activated protein kinase activation enhanced the differentiation to CD27IgD B cells, but it attenuated mTORC1 activation and differentiation into plasmablasts. High mTORC1 activation was noted in CD19 B cells of patients with SLE and correlated with plasmablast differentiation and disease activity. Taken together, differential metabolic reprogramming commits the differentiation of human unswitched memory B cells into plasmablasts (the combination of CpG and IFN-α amplifies mTORC1-glycolysis pathways) or CD27IgD memory B cells (CpG alone amplifies the AMP-activated protein kinase pathway). The former metabolic pathway may play a pivotal role in SLE.
ObjectivePlasmablasts play important roles in autoimmune diseases, including systemic lupus erythematosus (SLE). Activation of mechanistic target of rapamycin complex 1 (mTORC1) is regulated by amino acid levels. In patients with SLE, mTORC1 is activated in B cells and modulates plasmablast differentiation. However, the detailed mechanisms of amino acid metabolism in plasmablast differentiation remain elusive. We undertook this study to evaluate the effects of methionine in human B cells.MethodsPurified CD19+ cells from healthy donors (n = 21) or patients with SLE (n = 35) were cultured with Toll‐like receptor 7/9 ligand, interferon‐α (IFNα), and B cell receptor crosslinking, and we determined the types of amino acids that were important for plasmablast differentiation and amino acid metabolism. We also identified the transcriptional regulatory mechanisms induced by amino acid metabolism, and we assessed B cell metabolism and its relevance to SLE.ResultsThe essential amino acid methionine strongly committed cells to plasmablast differentiation. In the presence of methionine, Syk and mTORC1 activation synergistically induced methyltransferase EZH2 expression. EZH2 induced H3K27me3 at BTB and CNC homolog 2 (Bach2) loci and suppressed Bach2 expression, leading to induction of B lymphocyte–induced maturation protein 1 and X‐box binding protein 1 expression and plasmablast differentiation. CD19+ cells from patients with SLE overexpressed EZH2, which was correlated with disease activity and autoantibody production.ConclusionOur findings show that methionine activated signaling by controlling immunologic metabolism in B cells and played an important role in the differentiation of B cells into plasmablasts through epigenome modification of Bach2 by the methyltransferase EZH2.
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