Defective CD8 T Cell Memory Following Acute Infection Without CD4 T Cell Help

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 toListeria monocytogenesequal 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.