Abstract
Follicular helper T (T(FH)) cells are essential for generating protective humoral immunity. To date, microRNAs (miRNAs) have emerged as important players in regulating T(FH) cell biology. Here, we show that loss of miR-23~27~24 clusters in T cells resulted in elevated T(FH) cell frequencies upon different immune challenges, whereas overexpression of this miRNA family led to reduced T(FH) cell responses. Mechanistically, miR-23~27~24 clusters coordinately control T(FH) cells through targeting a network of genes that are crucial for T(FH) cell biology. Among them, thymocyte selection-associated HMG-box protein (TOX) was identified as a central transcription regulator in T(FH) cell development. TOX is highly up-regulated in both mouse and human T(FH) cells in a BCL6-dependent manner. In turn, TOX promotes the expression of multiple molecules that play critical roles in T(FH) cell differentiation and function. Collectively, our results establish a key miRNA regulon that maintains optimal T(FH) cell responses for resultant humoral immunity.