Department of Immunology and the Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA.
The CD8+ cytotoxic T cell response to pathogens is thought to be CD4+ helper T cell independent because infectious agents provide their own inflammatory signals. Mice that lack CD4+ T cells mount a primary CD8 response to Listeria monocytogenes equal to that of wild-type mice and rapidly clear the infection. However, protective memory to a challenge is gradually lost in the former animals. Memory CD8+ T cells from normal mice can respond rapidly, but memory CD8+ T cells that are generated without CD4 help are defective in their ability to respond to secondary encounters with antigen. The results highlight a previously undescribed role for CD4 help in promoting protective CD8 memory development.