Follicular regulatory T cells control humoral autoimmunity via NFAT2-regulated CXCR5 expression

Maturation of high-affinity B lymphocytes is precisely controlled during the germinal center reaction. This is dependent on CD4(+) CXCR5(+) follicular helper T cells (T-FH) and inhibited by CD4(+) CXCR5(+) Foxp3(+) follicular regulatory T cells (T-FR). Because NFAT2 was found to be highly expressed and activated in follicular T cells, we addressed its function herein. Unexpectedly, ablation of NFAT2 in T cells caused an augmented GC reaction upon immunization. Consistently, however, TFR cells were clearly reduced in the follicular T cell population due to impaired homing to B cell follicles. This was T-FR- intrinsic because only in these cells NFAT2 was essential to up- regulate CXCR5. The physiological relevance for humoral (auto-) immunity was corroborated by exacerbated lupuslike disease in the presence of NFAT2-deficient TFR cells.