Follicular Regulatory T Cells Regulate the Development of Cytotoxic-like Follicular Helper T Cells

T follicular regulatory (TFR) cells are found in the germinal center (GC) response and help shape the antibody (Ab) response. Whether TFR cells have a suppressive role, a helper role or both types of roles in the GC is unclear. Here, we addressed TFR cell function using 3 different strains of TFR cell mutant mice. After immunization, GC B cells but not T follicular helper (TFH) cell positively correlated with TFR cell levels. Using a gene profiling approach, we found that TFH cells from TFR-deficient mice showed strong up-regulation of granzyme B (Gzmb) and other effector CD8 T cell genes, many of which were Stat4 dependent. This aberrant cytotoxic T cell gene profile was increased in TFR-deficient mice crossed on a pro-inflammatory background. We detected Gzmb+ and Eomesodermin+ TFH cells and a higher rate of apoptotic GC B cells in the absence of TFR cells. Klrg1+ TFH cells expressed higher Gzmb and less IL-4 and IL-21. Our data show that TFR cells repress the development of abnormal cytotoxic TFH cells that correlate with a lower GC and Ab response. This data shows a novel mode of helper function for TFR cells in the GC response. Overall design: RNA sequenced from freshly isolated TFH cells of different mice with presence or loss of TFR cells