Suppression of Natural Killer Cell Activity by Monocytes Following Immunotherapy for Recurrent Spontaneous Aborters

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Abstract
PROBLEM: Natural killer (NK) cell activity has previously been shown to decrease in normal pregnancy as compared with the nonpregnancy state. The purpose of this study was to determine NK cell activity in recurrent aborters and to investigate the kinetics of NK cell activity following immunotherapy. METHODS: Recurrent aborters (N = 17) were immunized with husbands' mononuclear cells (1 × 108) twice during the early stage of current pregnancy. NK cell activity of recurrent aborters as well as that of normal pregnant (N = 12) and nonpregnant (N = 6) women (controls) was determined by 51Cr release assay. Monocytes were depleted from the mononuclear cell fraction and its effect on the NK cell activity was determined as well. RESULTS: At around 5 wk of gestation, NK cell activity in recurrent aborters before treatment was significantly higher (28.0 ± 5.1%) than that in normal pregnancy (18.9 ± 4.3%) (P < 0.01). Following immunotherapy, NK cell activity of recurrent aborters (N = 13) who maintained their pregnancy decreased significantly (21.7 ± 8.9%) (P < 0.05). In contrast, NK cell activity of recurrent aborters (N = 4) who aborted their current pregnancy did not decrease. Depletion of monocytes resulted in a significant increase in NK cell activity (P < 0.05). CONCLUSIONS: This study suggests that the immunotherapy induces suppression of NK cell activity which may contribute for the maintenance of pregnancy. Moreover, monocytes may be involved in this suppression.