KLRB1 and cytomegalovirus infection: These results indicate an expansion of CD300a+ on NK cell subsets (CD56bright and CD56dim) from healthy old individuals (all CMV-seropositive), likely associated with the combined effect of CMV infection and age, and a decrease of CD161+ NK cells related to CMV seropositivity (CD56dim NK cells) and age (CD56bright and CD56dim NK cells).