Most pronounced are the associations observed for the presence of KIR haplotype B/X, especially the telomeric B haplotype, and reduced HCMV infection or reactivation (52, 75–77, 82), which presumably could be explained by the presence of a higher number of activating KIR’s in the KIR B/X-haplotype as compared to the KIR AA-haplotype, facilitating NK cell mediated killing of virally infected cells. This evidence concerns the gene KIR3DL1 and cytomegalovirus infection.