Origins of CD4⁺ effector and central memory T cells

Lineage-committed effector CD4⁺ T cells are generated at the peak of the primary response and are followed by heterogeneous populations of central and effector memory cells. Here we review the evidence that T helper type 1 (T_H 1) effector cells survive the contraction phase of the primary response and become effector memory cells. We discuss the applicability of this idea to the T_H 2 cell, T_H 17 helper T cell, follicular helper T cell (T_FH cell) and induced regulatory T cell lineages. We also discuss how central memory cells are formed, with an emphasis on the role of B cells in this process.