Plasticity in the organization and sequences of human KIR/ILT gene families

The approximate to 1-Mb leukocyte receptor complex at 19q13.4 is a key poly morphic immunoregion containing all of the natural killer-receptor KIR and related ILT genes. When the organization of the leukocyte receptor complex was compared from two haplotypes, the gene content in the KIR region varied dramatically, with framework loci flanking regions of widely variable gene content. The ILT genes were more stable in number except for ILT6, which w as present only in one haplotype. Analysis of Alu repeats and comparison of KIR gene sequences, which are over 90% identical, are consistent with a re cent origin. KIR genesis was followed by extensive duplication/deletion as well as intergenic sequence exchange, reminiscent of MHC class I genes, whi ch provide KIR ligands.