New insights into follicular helper T cell response and regulation in autoimmune pathogenesis

Follicular helper T (Tfh) cells play a key role in driving B cell activation and differentiation during germinal center reactions in immune responses and autoimmune development, and these cells are characterized by high expression of CXCR5, PD1, ICOS, IL-21 and BCL6. Increasing evidence indicates that the functional dysregulation of Tfh cells contributes to the pathogenesis of autoimmune diseases, including primary Sjögren’s syndrome (pSS), which is a common autoimmune disease characterized by lymphocytic infiltration and tissue inflammation in salivary glands (SGs) and lacrimal glands that leads to dry mouth and dry eyes.1 Here, we provide a brief commentary on recent advances in understanding the Tfh cell response with a focus on new insights into Tfh cell regulation and therapeutic implications in autoimmune diseases.

Aryl hydrocarbon receptor activation drives polymorphonuclear myeloid-derived suppressor cell response and efficiently attenuates experimental Sjögren’s syndrome

Myeloid-derived suppressor cells(MDSCs)comprise heterogeneous myeloid cell populations with immunosuppressive capacity that contribute to immune regulation and tolerance induction.We previously reported impaired MDSC function in patients with primary Sjögren’s syndrome(pSS)and mice with experimental SS(ESS).However,the molecular mechanisms underlying MDSC dysfunction remain largely unclear.In this study,we first found that aryl hydrocarbon receptor(AhR)was highly expressed by human and murine polymorphonuclear MDSCs(PMN-MDSCs).Indole-3-propionic acid(IPA),a natural AhR ligand produced from dietary tryptophan,significantly promoted PMN-MDSC differentiation and suppressive function on CD4^(+)T cells.In contrast,feeding a tryptophan-free diet resulted in a decreased PMN-MDSC response,a phenotype that could be reversed by IPA supplementation.The functional importance of PMN-MDSCs was demonstrated in ESS mice by using a cell-depletion approach.Notably,AhR expression was reduced in PMN-MDSCs during ESS development,while AhR antagonism resulted in exacerbated ESS pathology and dysregulated T effector cells,which could be phenocopied by a tryptophan-free diet.Interferon regulatory factor 4(IRF4),a repressive transcription factor,was upregulated in PMN-MDSCs during ESS progression.Chromatin immunoprecipitation analysis revealed that IRF4 could bind to the promoter region of AhR,while IRF4 deficiency markedly enhanced AhR-mediated PMN-MDSC responses.Furthermore,dietary supplementation with IPA markedly ameliorated salivary glandular pathology in ESS mice with restored MDSC immunosuppressive function.Together,our results identify a novel function of AhR in modulating the PMN-MDSC response and demonstrate the therapeutic potential of targeting AhR for the treatment of pSS.