Different NK cell surface phenotypes defined by the DX9 antibody are due to KIR3DL1 gene polymorphism

KIR3DL1 and KIR3DL2 are NK cell receptors for polymorphic HLA-E and -A dete rminants. The proportion of NK cells that bind anti-KIR3DL1-specific Ab DX9 and their level of binding vary between individuals. To determine whether these differences are due to KIR polymorphism, we assessed KIR3D gene diver sity in unrelated individuals and families. Both KIR3DL1 and KIR3DL2 are hi ghly polymorphic genes, with KIR3DS1 segregating like an allele of KIR3DL1, A KIR haplotype lacking KIR3DL1 and KIR3DS1 was defined, The two KIR3DL1 a lleles of a heterozygous donor were expressed by different, but overlapping , subsets of NK cell clones. Sequence variation in KIR3DL1 and KIR3DL2 appe ar distinct; recombination is more evident in KIR3DL1, and point mutation i s more evident in KIR3DL2. The KIR3DL1 genotype correlates well with levels of DX9 binding by NK cells, but not with the frequency of DX9-binding cell s. Different KIR3DL1 alleles determine high, low, and no binding of DX9 Ab, Consequently, heterozygotes for high and low binding KIR3DL1 alleles have distinct subpopulations of NK cells that bind DX9 at high and low levels, g iving characteristic bimodal distributions in how cytometry, The Z27 Ab gav e binding patterns similar to those of DX9, Four KIR3DL1 alleles producing high DX9 binding phenotypes were distinguished from four alleles producing low or no binding phenotypes by substitution at one or more of four positio ns in the encoded protein: 182 and 283 in the extracellular Ig-like domains , 320 in the transmembrane region, and 373 in the cytoplasmic tail.