Niclosamide suppresses the expansion of follicular helper T cells and alleviates disease severity in two murine models of lupus via STAT3

Background Autoantibody production against endogenous cellular components is pathogenic feature of systemic lupus erythematosus (SLE). Follicular helper T (T FH ) cells aid in B cell differentiation into autoantibody-producing plasma cells (PCs). The IL-6 and IL-21 cytokine-mediated STAT3 signaling are crucial for the differentiation to T FH cells. Niclosamide is an anti-helminthic drug used to treat parasitic infections but also exhibits a therapeutic effect on autoimmune diseases due to its potential immune regulatory effects. In this study, we examined whether niclosamide treatment could relieve lupus-like autoimmunity by modulating the differentiation of T FH cells in two murine models of lupus. Methods 10-week-old MRL/ lpr mice were orally administered with 100 mg/kg of niclosamide or with 0.5% methylcellulose (MC, vehicle) daily for 7 weeks. TLR7 agonist, resiquimod was topically applied to an ear of 8-week-old C57BL/6 mice 3 times a week for 5 weeks. And they were orally administered with 100 mg/kg of niclosamide or with 0.5% MC daily for 5 weeks. Every mouse was analyzed for lupus nephritis, proteinuria, autoantibodies, immune complex, immune cell subsets at the time of the euthanization. Results Niclosamide treatment greatly improved proteinuria, anti-dsDNA antibody levels, immunoglobulin subclass titers, histology of lupus nephritis, and C3 deposition in MRL/ lpr and R848-induced mice. In addition, niclosamide inhibited the proportion of T FH cells and PCs in the spleens of these animals, and effectively suppressed differentiation of T FH -like cells and expression of associated genes in vitro. Conclusions Niclosamide exerted therapeutic effects on murine lupus models by suppressing T FH cells and plasma cells through STAT3 inhibition.