CXCR5+ T cells: follicular homing takes center stage in T-helper-cell responses

The development of effector and memory T cells is a multistep and spatially controlled process. Resting T helper (Th) cells are primed during antigen-specific contact with dendritic cells in the T-cell zone of secondary lymphoid tissues and then, develop further to become specialized effector or memory T cells. Chemokines are key players in the control of cellular traffic. Here, we argue for a crucial role for the chemokine B-cell-attracting chemokine 1 (BCA-1/CXCL13) and its receptor CXC-chemokine receptor 5 (CXCR5) in the follicular homing and further differentiation of newly primed, nonpolarized Th cells. The rapid induction of this follicular localization program in these cells supports the concept of an unprecedented role for the B-cell compartment in Th-cell responses.