IL18 and cytomegalovirus infection: However, somewhat unexpectedly, when we stratified the data by HCMV infection status, postvaccination enhancement of NK cell IFN-γ responses to high concentrations of IL-12 plus IL-18 was observed only among HCMV+ individuals, in whom the frequencies of responding cells approached those consistently observed in HCMV− individuals (Fig. 7G).