The transcription factor Foxp1 is a critical negative regulator of the differentiation of follicular helper T cells

Abstract

CD4+ follicular helper T cells (T FH cells) are essential for germinal center (GC) responses and long-lived antibody responses. Here we report that naive CD4+ T cells deficient in the transcription factor Foxp1 'preferentially' differentiated into T FH cells, which resulted in substantially enhanced GC and antibody responses. We found that Foxp1 used both constitutive Foxp1A and Foxp1D induced by stimulation of the T cell antigen receptor (TCR) to inhibit the generation of T FH cells. Mechanistically, Foxp1 directly and negatively regulated interleukin 21 (IL-21); Foxp1 also dampened expression of the costimulatory molecule ICOS and its downstream signaling at early stages of T cell activation, which rendered Foxp1-deficient CD4+ T cells partially resistant to blockade of the ICOS ligand (ICOSL) during T FH cell development. Our findings demonstrate that Foxp1 is a critical negative regulator of T FH cell differentiation. © 2014 Nature America, Inc. All rights reserved.