Follicular helper T cells
, or ThF
cells, are antigen
-experienced CD4+ T cells
found in the lymph node
and are identified as being PSGL-1- and CXCR5+. ThF cells are found at the periphery of B cell
follicles and appear to mediate naïve B cell activation and germinal center formation, probably through the expression of ligand
and the secretion of Th1
– and Th2
. It is possible that ThF cells might arise as branches in the Th1 and Th2 differentiation pathways but their precise lineage relationship to the other effector CD4+
T cell subsets is still uncertain.
Inducible T-cell co-stimulator (CD278 or ICOS) has proven to be a particularly critical signal for ThF cells, although it is not clear if that role is in induction or progressive maturation. Also Bcl-6 is a factor identified in ThF cells, but it may have roles that extend beyond this subset, because it has been implicated in memory CD8+ T cell development.
Finally, it has been shown that dysregulated ThF cells can cause systemic autoimmunity and auto-antibody production or contribute to T cell–mediated organ-specific autoimmunity.