Role of lymphokine-secreting CD8+ T cells in cytotoxic T lymphocyte responses against vaccinia virus.

The present study has examined the relative role of CD4+ and CD8+ Th cells in the generation and reactivation of antivaccinia virus memory CTL responses. We show that mice primed in vivo to vaccinia virus generate in vitro antivaccinia virus memory CTL responses through both CD4+ and CD8+ Th cell pathways, with the CD4+ Th pathway being the more prominent of the two. In addition, we show that vaccinia virus-specific CD8+ Th cell function is mediated through production of lymphokines, including IL-2, and that the CD8+ Th cell component in the CTL response is labile, decreasing progressively with increasing time after in vivo priming. Thus, this study demonstrates the existence of two phenotypically distinct Th cell pathways in the generation of antivirus CTL responses.