Infection with cytomegalovirus (Béziat et al. 2013a), KIR gene copy number variation (Béziat et al. 2013b), and polymorphisms in KIR promotor regions (Bruijnesteijn et al. 2020) also directly impact KIR expression level or the number of KIR expressing NK cells. Here, KIR3DL1 is linked to infection.