Bcl6 expression specifies the T follicular helper cell program in vivo

T follicular helper (Tfh) cells play a pivotal role in germinal center reactions, which requires Bcl6 transcription factor. To analyze their relationships with other effector T cell lineages and their stability in vivo, we developed and analyzed a new Bcl6 reporter mouse alone or together with other lineage reporter systems. Assisted with genome-wide transcriptome analysis, we show substantial plasticity of T cell differentiation in the early phase of immune response. At this stage, CXCR5 appears to be expressed in a Bcl6-independent manner. Once Bcl6 is highly expressed, Tfh cells can persist in vivo and some of them develop into memory cells. Together, our results indicate Bcl6 as a bona fide marker for Tfh polarized program. Three group of samples, with 2 biological replicates within each group and total of 6 samples were analyzed.