Recurrent miscarriage is associated with a decline of decidual natural killer cells expressing killer cell immunoglobulin‐like receptors specific for human leukocyte antigen C

Aim To investigate the relationship between natural killer ( NK ) cell phenotype and recurrent miscarriage ( RM ). Methods We studied killer cell immunoglobulin‐like receptor ( KIR ) expression on decidual NK cells in women with RM . Results The expression of KIR2DL1/S1 on CD 56 + CD 16 − NK cells in the deciduas of these women was significantly lower than in that of control subjects ( P  = 0.026). There was a significant decline in the frequency of CD 56 + CD 16 − NK cells staining for KIR2DL1/S1 and KIR2DL2/S2/L3 throughout the first trimester in patients ( P  < 0.05). Furthermore, by stratification of the women in three groups according to gestational stage, it was found that KIR2DL1/S1 expressing NK cells were significantly decreased in all groups, especially around gestational days 50–70 ( P  = 0.010). Conclusion This is the first report to demonstrate that RM is associated with a decline in the frequency of decidual NK cells expressing KIR specific for human leukocyte antigen ( HLA )‐ C , and in which gestational stage was considered. The results suggest that KIR phenotype contributes to the pathogenesis of the disease, and that assessment of KIR may serve as a diagnostic tool.