Four killer cell Ig-like receptor (KIR) genes, collectively referred to as framework genes, characterize almost all KIR haplotypes. In particular, KIR3DL3 and KIR3DL2 mark the ends of the locus, whereas KIR3DP1 and KIR2DL4 are located in the central part. A recombination hot spot, mapped between KIR3DP1 and KIR2DL4, splits the haplotypes into two regions: a centromeric (Cen) region (spanning from KIR3DL3 to KIR3DP1) and a telomeric region (from KIR2DL4 to KIR3DL2), both varying in KIR gene content. In this study, we analyzed KIR3DP1 polymorphism in a cohort of 316 healthy, unrelated individuals. To this aim, we divided KIR3DP1 alleles into two groups by the use of a sequence-specific primer-C PCR approach. Our data clearly indicated that KIR3DP1 alleles present on haplotypes carrying Cen-A or Cen-B1 regions differ from those having Cen-B2 motifs. Few donors (~3%) made exceptions, and they were all, except one, characterized by uncommon haplotypes, including either KIR deletions or KIR duplications. Consequently, as KIR2DL1 is present in Cen-A and Cen-B1 regions but absent in Cen-B2 regions, we demonstrated that KIR3DP1 polymorphism might represent a suitable marker for KIR2DL1 gene copy number analysis. Moreover, because Cen-B1 and Cen-B2 regions are characterized by different KIR3DP1 alleles, we showed that KIR3DP1 polymorphism analysis also provides information to dissect between Cen-B1/Cen-B1 and Cen-B1/Cen-B2 donors. Taken together, our data suggest that the analysis of KIR3DP1 polymorphism should be included in KIR repertoire evaluation.
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