Genotyping of natural killer cell immunoglobulin-like receptors in human early reproductive losses.

Genotyping of killer cell immunoglobulin-like receptors (KIR) of NK-cells was performed in 634 women with early pregnancy losses (EPL), including 158 women with recurrent implantation failure (RIF) after at least three IVF cycles, and 110 women with at least two intrauterine pregnancy losses characterized by clinically confirmed retention of a non-viable fetus in the uterus without spontaneous miscarriage, defined as recurrent pregnancy loss (RPL). The control group consisted of 431 women with at least two healthy children. In the RIF, a significant shift in the frequency of KIR-genotypes was observed compared with both the control and the RPL groups. A significantly higher frequency of the KIR-AA genotype was observed in the RIF group compared to the control group (χ² = 26.78; p < 0.0001; OR = 2.7) and the RPL group (χ² = 15.83; p < 0.0001; OR = 2.86). Analysis of the frequency of full-length/deletion alleles of KIR2DS4 among AA genotype carriers showed an increased frequency of the 2DS4-del in the RIF compared with the RPL and control groups. A significantly higher frequency of the cenAA was also observed in RIF compared with the control (χ² = 20.10; p < 0.0001) and the RPL(χ² = 12.05; p < 0.005). The significantly increased frequency of the KIR-AA genotype with predominance of deletion KIR2DS4 alleles, along with the elevated frequency of the cenAA in RIF, may indicate insufficient NK-cell activation at the stage of embryo implantation. These findings suggest different etiological mechanisms for RIF and RPL.