Complex memory T-cell phenotypes revealed by coexpression of CD62L and CCR7

Antigen-experienced T cells have been divided into CD62L(+) CCR7(+) central memory (T-CM) and CD62L(-) CCR7(-) effector memory (T-EM) cells. Here, we examined coexpression of CD62L and CCR7 in lymphocytic choriomeningitis virus-specific memory CD8 T cells from both lymphoid and nonlymphoid tissues. Three main points emerged: firstly, memory cells frequently expressed a mixed CD62L(-) CCR7(+) phenotype that differed from the phenotypes of classical T-EM and T-CM cells; secondly, T-EM cells were not restricted to lymphoid organs but were also present in significant numbers in nonlymphoid tissues; and thirdly, a major shift from a T-CM to T-EM phenotype was found in memory cells that had been stimulated repetitively with antigen.