Naive CD8 T cells express relatively few trafficking molecules (e.g., CD62L, CCR7 and LFA-1). However, following sufficient antigenic and costimulatory activation, CD8 T cells will rapidly proliferate and expand. In addition to this marked expansion, effector CD8 T cells lose expression of CD62L and CCR7, while gaining the expression of P- and E-selectin ligands, inflammatory chemokine receptors (e.g., CXCR3 and CCR5) and additional integrins (e.g., VLA-1, VLA-4, α4 and β7), resulting in efficient recruitment of these cells to inflamed tissues. Following contraction, 90–95% of the effector cells die via apoptosis. However, the CD8 T cells that survive the contraction phase are maintained long term and progress into memory cells. Collectively, memory CD8 T-cell populations contain a heterogeneous mixture of cells that express a variety of trafficking molecules, shared with both naive and effector CD8 T cells.
ESelL: E-selectin ligands; LFA: Lymphocyte function-associated antigen; PSelL: P-selectin ligands; VLA: Very-late antigen.