Аннотация:Helper T cells are critical for protective immunity, CD8 + T-cell memory, and CD4 + recall responses, but whether the same or distinct CD4 + T cells are involved in these responses has not been established. Here we describe two CD4 + T cells, LLO118 and LLO56, specific for an immunodominant Listeria monocytogenes epitope, with dramatically different responses to primary and secondary infection. Comparing in vivo responses, LLO118 T cells proliferate more strongly to primary infection, whereas surprisingly, LLO56 has a superior CD4 + recall response to secondary infection. LLO118 T cells provide more robust help for CD8 + T-cell responses to secondary infection than LLO56. We found no detectable differences in antigen sensitivity, but naive LLO118 T cells have much lower levels of CD5 and their T-cell receptor levels are dramatically down-regulated after their strong primary response. Thus, distinct CD4 + helper T cells are specialized to help either in primary or secondary responses to infection.
