Calycosin synergizes with methotrexate in the treatment of Sjögren's disease by targeting BATF in T follicular helper cells.

T follicular helper (Tfh) cells are crucially involved in the pathogenesis of autoimmune disorders, including Sjögren's disease (SjD, also known as Sjögren's syndrome), by promoting effector B cell responses and autoantibodies production. However, targeting Tfh cells remains challenging. In this study, we identified that calycosin (Caly), a natural flavonoid, effectively suppressed pathogenic Tfh cell responses, although it did not affect the plasmacytic differentiation of B cells. Under Tfh polarization conditions, Caly rapidly bound to the master transcription factor, BATF, in both human and murine CD4⁺ T cells and thus potently disrupted BATF-mediated Maf gene transcription. Methotrexate (MTX), a first-line medication in the treatment of autoimmune disorders, mainly suppresses B cell responses but fails to target Tfh cells. In a mouse model of experimental Sjögren's syndrome (ESS) that we previously established, MTX synergized with Caly in attenuating the disease pathology and autoantibodies in ESS mice with chronic inflammation, with signs of disease remission. This immunomodulatory function was also validated in peripheral blood mononuclear cells from patients with SjD. Thus, Caly may serve as a novel inhibitor of BATF in suppressing Tfh-cell-mediated humoral autoimmunity and elicit a synergistic effect in combination with B-cell-targeting strategies.