Genomic organization of the KIR locus.KIR genes segregate into groups A and B haplotypes. Framework genes located at the ends and in the central part of the locus (gray boxes) define 2 haplotype segments: the centromeric (Cen) and the telomeric (Tel). Common centromeric and telomeric segments are shown. In the A haplotype, KIR2DL1 and KIR2DL3 are found in the centromeric segment and KIR3DL1 and KIR2DS4 in the telomeric. Combinations of KIR2DL1/L2/L5/S2/S3/S5 are found in B-haplotype centromeric segments and combinations of KIR2DL5/S1/S3/S5 and KIR3DS1 in B-haplotype telomeric segments.