CD4 and infection: IAV‐specific CD8+ cytotoxic T lymphocytes and IFN‐γ‐producing CD4+ T lymphocytes promote clearance of IAV and recovery from infection.5 Intranasal HA–SF–10 activated IFN‐γ‐producing lymphocytes in the nasopharynx and NALT and probably stimulated cellular immunity against IAV.