Human polymorphonuclear leukocyte phagocytosis in pregnancy. Development of inhibition during gestation and recovery in the postpartum period.

The phagocytosis of S. aureus by normal human PMN leukocytes was inhibited by pregnancy serum. Control sera from normal adult nulliparous women, from men, and from cord blood all functioned normally in support of phagocytosis. However, particle ingestion was reduced significantly (p less than 0.001) when leukocytes were in 15% pregnancy serum obtained at term. To determine at what stage in pregnancy the inhibition of phagocytosis could first be detected, sera were obtained from multiple pregnant donors and pooled according to week of gestation. Significantly fewer bacteria were ingested in each of the serum pools obtained after week 16 of pregnancy and the inhibitory effect persisted through gestation. Following delivery, less inhibition was detected as early as 2 days post partum. Phagocytosis assays were performed in six matched maternal and cord serum pairs. Five of the six maternal sera showed inhibition of phagocytosis; one pregnancy and all cord sera functioned normally in support of bacterial ingestion by normal granulocytes. Since neutrophils are essential to the development of rheumatoid arthritis and certian other inflammatory disorders, the subsidence of these diseases during gestation and their exacerbation post partum could be related, at least in part, to the inhibitory effects of pregnancy serum on leukocyte functions.