IFNG and pertussis: Because our previous work has indicated that NK cell IFN-γ production after restimulation with vaccine Ags is cytokine dependent (3), we predicted that fewer NK cells from HCMV+ donors would produce IFN-γ in response to pertussis or influenza Ags because of the reduced capacity of the expanded CD56dimCD57+NKG2C+ subset to respond to cytokines.