Based on our observation of a major decline in the production of IL-2 in aged human PBMC in response to influenza challenge (unpublished data) and in vitro studies in the mouse, we designed experiments to evaluate the effect of possible key cytokines including IL-2, IL-6, IL-4, IL-10, and IL-17A, on the generation of cytotoxic effector CD8+ T cells in response to influenza virus. The gene discussed is IL4; the disease is influenza.