miR-155 expression associates with pathogenic circulating follicular helper T-cell phenotype in myasthenia gravis

INTRODUCTION: Myasthenia gravis (MG) is an antibody-mediated autoimmune disease targeting neuromuscular junctions. We previously reported that ICOS-high expressing circulating follicular T cells (ICOShighcTfh) are expanded in MG and are associated with the disease severity. Although it is unknown what influences the skew of Tfh in MG, one of the candidates is microRNA (miRNA), especially miR-146a and miR-155, which were reported to be associated with accumulation and function of Tfh. METHODS: Twenty-four MG patients positive for anti-acetylcholine receptor antibody and 12 HS were enrolled. The expressions of miR-146a and miR-155 in peripheral blood mononuclear cells (PBMCs) were analyzed by a real-time PCR system in association with the cTfh phenotype in MG. To further examine cell-type-specific MIR155HG expression, publicly available single-cell RNA sequencing (scRNA-seq) data from MG patient PBMCs were analyzed. RESULTS: The expressions of miR-146a and miR-155 were significantly higher in MG than HS. The level of miR-155 but not miR-146a level showed significant correlation with the frequency of ICOShighcTfh. scRNA-seq analysis revealed that MIR155HG was most highly expressed in a Tfh-like CD4+ T cell cluster characterized by elevated CXCR5, ICOS, PDCD1, and IL21, which was expanded in MG relative to HS (24% vs. 18%), supporting the PBMC-level miRNA findings. miR-155 levels decreased after immunotherapy, paralleling the reduction of ICOShighcTfh in MG. CONCLUSION: Elevated miR-155 expression is associated with pathogenic activation of circulating Tfh cells in MG, supported by single-cell transcriptomic evidence of MIR155HG enrichment in a Tfh-like CD4+ T cell population.