CD4 and infection: This raises the following questions: (1) weather the kinetics of CD8+/CD4+ responses during AIV infection are similar to those observed during a mild influenza disease; (2) whether CD8+ T cell responses are mainly protective or could also be immunopathogenic; (3) whether the expanded CD8+ T cell responses are derived predominantly from the memory pools or possibly recruited from naïve precursors; and (4) what is the relationship between CD8+ T cells, CD4+ T cells, and humoral immunity.