Lineage commitment and differentiation into CD4+ T cell subsets reflect an interplay between chromatin regulators and transcription factors (TF). Follicular T cell development is regulated by the Bcl6 TF, which helps determine the phenotype and follicular localization of both CD4+ follicular helper T cells (TFH) and follicular regulatory T cells (TFR). Here we show that Bcl6-dependent control of follicular T cells is mediated by a complex formed between Bcl6 and the Mi-2β-nucleosome-remodeling deacetylase complex (Mi-2β-NuRD). Formation of this complex reflects the contribution of the intracellular isoform of osteopontin (OPN-i), which acts as a scaffold to stabilize binding between Bcl6 and the NuRD complex that together regulate the genetic program of both TFH and TFR cells. Defective assembly of the Bcl6-NuRD complex distorts follicular T cell differentiation, resulting in impaired TFR development and skewing of the TFH lineage toward a TH1-like program that includes expression of Blimp1, Tbet, granzyme B, and IFNγ. These findings define a core Bcl6-directed transcriptional complex that enables CD4+ follicular T cells to regulate the germinal center response.
Keywords: Bcl6 transcription factor; follicular helper T cells; follicular regulatory T cells; germinal center response; osteopontin.