The described gene induction of KIR2DL3 after YFV vaccination might therefore have been restricted to other KIR-expressing cell populations, such as T cells, as only bulk KIR2DL3 mRNA levels on whole blood were quantified in the study by Gaucher et al. As previous studies also suggested an influence of HCMV infection on NK cell expansion (14, 16, 30), we assessed the HCMV status of our study subjects, and did not observe any differences in frequencies of tetramer+ KIR2DL2/3+ NK cells between HCMV+ and HCMVneg individuals. Here, KIR3DL1 is linked to cytomegalovirus infection.