Elevated Natural Killer Cells in the Decidua and Peripheral Blood of Patients with Unexplained Recurrent Miscarriage

OBJECTIVE: To assess natural killer (NK) cell location, phenotype, and quantity within decidua and peripheral blood of patients with unexplained recurrent miscarriage (URM), and to seek feasible detection methods and develop standardized methods for NK cell differentiation in the peripheral blood in URM. STUDY DESIGN: Decidual samples were collected from URM cases (n=35) and normal pregnancies (n=27) after curettage and evaluated via double-label immunofluorescence. Dynamic peripheral blood NK (PBNK) cells were followed for 5 months post-curettage in URM cases and normal nonpregnant women, evaluated by flow cytometry. Nonparametrical Mann-Whitney U tests were used during the analysis. RESULTS: NK cells aggregated around blood vessels in decidua. The CD56(+)CD16(+)NK cell numbers in decidua and peripheral blood and CD56(+)CD16(+)/CD56(+)CD16(-) NK cell ratio in decidua in URM were significantly greater than in normal pregnancy (p<0.05). CD56(+)CD16(+)NK cells in peripheral blood of URM increased more than that in normal nonpregnant women at 4 months post-curettage and recovered to baseline at 5 months post-curettage. CONCLUSION: Overaccumulation of CD56(+)CD16(+)NK cells might be related to abnormal vessel reconstruction during embryo implantation at the maternal-fetal interface, which occurs more frequently in URM. Subsequent pregnancy should be scheduled after the return of PBNK cell levels to normal.