CXCR5-negative natural killer cells ameliorate experimental autoimmune myasthenia gravis by suppressing follicular helper T cells

BACKGROUND: Recent studies have demonstrated that natural killer (NK) cells can modulate other immune components and are involved in the development or progression of several autoimmune diseases. However, the roles and mechanisms of NK cells in regulating experimental autoimmune myasthenia gravis (EAMG) remained to be illustrated. METHODS: To address the function of NK cells in experimental autoimmune myasthenia gravis in vivo, EAMG rats were adoptively transferred with splenic NK cells. The serum antibodies, and splenic follicular helper T (Tfh) cells and germinal center B cells were determined by ELISA and flow cytometry. The roles of NK cells in regulating Tfh cells were further verified in vitro by co-culturing splenocytes or isolated T cells with NK cells. Moreover, the phenotype, localization, and function differences between different NK cell subtypes were determined by flow cytometry, immunofluorescence, and ex vivo co-culturation. RESULTS: In this study, we found that adoptive transfer of NK cells ameliorated EAMG symptoms by suppressing Tfh cells and germinal center B cells. Ex vivo studies indicated NK cells inhibited CD4(+) T cells and Tfh cells by inducing the apoptosis of T cells. More importantly, NK cells could be divided into CXCR5(-) and CXCR5(+) NK subtypes according to the expression of CXCR5 molecular. Compared with CXCR5(-) NK cells, which were mainly localized outside B cell zone, CXCR5(+) NK were concentrated in the B cell zone and exhibited higher expression levels of IL-17 and ICOS, and lower expression level of CD27. Ex vivo studies indicated it was CXCR5(-) NK cells not CXCR5(+) NK cells that suppressed CD4(+) T cells and Tfh cells. Further analysis revealed that, compared with CXCR5(-) NK cells, CXCR5(+) NK cells enhanced the ICOS expression of Tfh cells. CONCLUSIONS: These findings highlight the different roles of CXCR5(-) NK cells and CXCR5(+) NK cells. It was CXCR5(-) NK cells but not CXCR5(+) NK cells that suppressed Tfh cells and inhibited the autoimmune response in EAMG models.