Cutting edge: local recall responses by memory T cells newly recruited to peripheral nonlymphoid tissues.

Infection results in the formation of a circulating effector memory T cell population able to enter peripheral tissues either in the steady state or in response to localized infection. As a consequence, recall is thought to result from a phased response first involving those T cells already at the site of infection followed by the infiltration of memory cells from the wider circulation. We have recently reported that tissue-resident T cells can undergo stimulation and proliferation in response to local infection. In this study, we examine the proliferation of memory T cells newly recruited from the circulation. Our results show that although recruitment of circulating memory cells is nonspecific in nature, there is preferential proliferation of specific T cells within infected tissues. Thus, expansion represents a means of local Ag-specific enrichment of T cells recruited from a circulating memory pool of mixed specificities.