DISTRIBUTION OF KILLER-CELL IMMUNOGLOBULIN-LIKE RECEPTORS (KIR) AND THEIR HLA CLASS I LIGANDS IN THE BULGARIAN POPULATION

Killer-cell immunoglobulin-like receptors (KIR) and their corresponding ligands are the main regulators of natural killer cells function. Herein, we analyzed KIR gene and genotype diversity, and KIR HLA class I ligands in the Bulgarian population and compared the results with those published for other human populations. Thirty-three different KIR genotypes were observed, one of which had not been previously described. The most frequent KIR genotype (ID1) corresponded to the homozygous KIR A haplotype (AA). KIR HLA ligand typing demonstrated prevalence of C1/C2 heterozygosity (52.4%) over C1 (31.5%) and C2 (16.1%) homozygosity. The carriers of HLA-BBw4 amounted to 72.6%. Analysis of co-presence of inhibitory KIR+/-activating KIR+HLA ligand revealed that each of the individuals studied possessed at least one inhibitory KIR/HLA ligand pair. The observed KIR and HLA class I ligand gene frequencies and the genotypes that they form demonstrated high similarity between Bulgarians and other Caucasians, but great difference from non-Caucasians. Predominance of inhibitory KIR/ligands genotypes in our population, together with the data for higher frequencies of inhibitory in comparison to activating KIRs and prevalence of KIR A haplotypes support the positive selection of inhibitory KIR combinations in different populations worldwide.