Antigen-specific memory T cells are a critical component of protective immunity because of their increased frequency and enhanced reactivity after restimulation. However, it is unclear whether 'memory-like' T cells generated during lymphopenia-induced homeostatic proliferation can also offer protection against pathogens. Here we show that homeostatic proliferation-induced memory (HP-memory) CD8+ T cells controlled bacterial infection as effectively as 'true' memory CD8+ T cells, but their protective capacity required the presence of CD4+ T cells during homeostatic proliferation. The necessity for CD4 help was overcome, however, if the HP-memory CD8+ T cells lacked expression of TRAIL (tumor necrosis factor-related apoptosis-inducing ligand; also called Apo-2L). Thus, like conventional CD8+ memory T cells, the protective function of HP-memory CD8+ T cells shows dependence on CD4+ T cell help.
Bibliographical noteFunding Information:
We thank T. Griffith for providing TRAIL-deficient mice; and K. Hogquist, M. Jenkins, M. Mescher and members of the Jamequist lab for input. Supported by the National Institutes of Health (S.C.J. and S.P.S.), the Centers for Disease Control (S.C.J.), the American Cancer Society (S.P.S.), the National Cancer Institute (T32 CA009138 to S.E.H.), the American Cancer Society (S.E.H.) and the Irvington Institute (M.C.W.).