Local development of effector and memory T helper cells.

Clonal evolution underpins all facets of adaptive immunity. In particular, antigen-specific helper T (Th) cell development is central to high-affinity B cell immunity and protective vaccination. Dendritic cell maturation and TCR affinity-based selection mechanisms control the recruitment and effective propagation of preferred antigen-specific Th cell cohorts in local lymphoid tissue. Importantly, follicular B helper T (T(FH)) cells emerge as the specialized local effector Th cells that orchestrate the stepwise development of B cell immunity in these local environments. Recent studies also introduce the role of persistent antigen in the development of effector Th cells with evidence for long-term antigen depots that might contribute to local antigen-specific Th cell memory.