Id2 is required for antiviral Th1 cell differentiation and represses Tfh cell differentiation

Differentiation of naive CD4+ T cells into T-helper (Th) effector subsets is critical for protection against pathogens. Together, E-protein transcription factors and the inhibitor-of-DNA binding (Id) proteins are important arbiters of T cell development, but their role in the differentiation of Th1 and Tfh cells is not well understood. Th1 cells show robust Id2 expression compared to Tfh cells, and RNAi depletion of Id2 increased Tfh cell frequencies and germinal center responses, while impairing Th1 cell accumulation during viral infection. Further, Th1 cell differentiation was blocked by genetic ablation of Id2, leading to E-protein dependent accumulation of effector cells with 78% of Th1-associated genes showing diminished expression and a concurrent enrichment of the Tfh gene-expression program. The Tfh-defining transcriptional repressor Bcl6 bound to the Id2 locus inhibiting expression, providing a mechanism by which bimodal expression of Id2 in Tfh and Th1 cells can be established. Thus, Id2 is critical in enforcing the reciprocal development of Th1 and Tfh cell fates. We used microarray to assess the changes in gene expression between Id2-sufficient and -deficient Th1 and Tfh cells. Id2-sufficient and -deficient SMARTA CD4+ T cells were sorted into TriZol on day 7 of LCMV infection according to expression of SLAM and CXCR5. Two replicates per sample were analyzed.