Frequencies of killer immunoglobulin-like receptor genotypes influence susceptibility to spontaneous abortion

Natural killer (NK) cells are the most abundant lymphocyte population in the decidua. These cells express killer immunoglobulin-like receptors (KIRs), which upon recognition of HLA class I molecules on trophoblasts may either stimulate NK cells (activating KIRs) or inhibit them (inhibitory KIRs) to produce soluble factors necessary for the maintenance of pregnancy.KIR genes exhibit extensive haplotype polymorphism; individuals differ in both the number and kind (activating vs. inhibitory) ofKIR genes. This polymorphism affects NK cell reactivity and susceptibility to diseases, including gynecological disorders. Therefore weKIR-genotyped 149 spontaneously aborting women and 117 control multiparae (at least 2 healthy-born children). Several genotypes (i.e. combinations of variousKIR genes) were differently distributed among the patients and control subjects. Differences were observed in the numbers and the ratios of activating to inhibitory KIRs between patients and healthy women: (i) genotypes containing 6 activatingKIR genes were less frequent and those containing 6 inhibitoryKIR genes were more frequent in patients than in control subjects, and (ii) an excess of inhibitory KIRs (activating-to-inhibitoryKIR gene ratios of 0.33 to 0.83) was associated with miscarriage, whereas ratios close to equilibrium (0.86–1.25) seemed to be protective. In addition, the results suggest for the first time that sporadic and recurrent spontaneous abortions as well as miscarriage in the presence or absence of autoantibodies may have differentKIR genotypic backgrounds.