From naive to memory. Development and regulation of CD4+ T cell responses.

Specific immune responses proceed through and are regulated at several stages: activation of naive cells and their differentiation into effector cells, completion of effector functions, development of memory cells, and subsequent reactivation of memory cells. To understand the development and regulation of CD4+ T cells in immune responses, naive CD4+ T cells were enriched from T cell receptor (TCR) transgenic mice, and used to generate effector and memory populations in vivo and in vitro. The expression of a common TCR on all of these developmental subsets has allowed us to compare directly their phenotype, cytokine profiles, activation requirements, and susceptibility to apoptosis. Our experiments have revealed interesting distinctions among naive, effector, and memory subsets of CD4+ T cells and have important implications for our understanding of immune responses.