Abstract
T follicular helper (TFH) cells are a helper T-cell subset that is defined by their localisation to B-cell areas of secondary lymphoid tissues, enabling them to provide their B-cell helper function. Precursors of TFH cells migrate to the B-cell follicles by upregulating CXCR5 and downregulating CCR7, a process that can be blocked by S1PR1 overexpression. TFH cells and their precursors also express the early activation antigen CD69, which is a negative regulator of S1PR1. In this study, we tested the hypothesis that CD69 expression by TFH cells is important for their differentiation and localisation after immunization. Genetic deletion of CD69 on TFH cells and a proportion of their precursors did not alter their formation, nor their ability to support high-affinity B-cell responses. This demonstrates that although CD69 is expressed highly on TFH cells, it is not necessary for their formation or their B-cell helper functions in lymph nodes (LNs).