The 3 HCMV seropositive participants in each group were evenly distributed across the CD56dim CD57+NKG2C+ and CD57+FCεR1γ- frequency range suggesting HCMV infection (known to expand populations of highly differentiated and adaptive NK cells13), was not driving the differences observed between the two groups (Supplementary Fig. 4f). Here, KLRC2 is linked to cytomegalovirus infection.