Studies Of The Effects Of Pregnancy Serum On Polymorphonuclear Leukocyte Functions

The phagocytosis of both viable and heat‐killed Staphylococcus aureus by normal human neutrophils was diminished in the presence of pregnancy serum. Particle ingestion was reduced significantly ( P < 0.0025) after 5 minutes of incubation when leukocytes were in 15% serum obtained during the latter phases of gestation. Control sera from normal adult females or males or from cord blood all functioned normally in support of phagocytosis. Intracellular metabolic events occurring after ingestion, including bacterial killing and nitro‐blue tetrazolium reduction, were decreased in proportion to the number of particles ingested. Differential studies involving leukocytes obtained from either pregnant or control subjects, when suspended in either pregnancy or control serum pools, showed the inhibition was due to a humoral and not a cellular factor. Mixing experiments demonstrated that serum obtained during gestation contained a suppressor or neutrophil function rather than a deficiency of a factor required for phagocytosis. The pregnancy serum suppressant affected cells, not the particles ingested, and was found to be non‐dialyzable and heat‐stable. Hydrocortisone added to control sera to exceed the steroid concentrations found in pregnancy sera did not retard phagocytosis nor diminish bactericidal activity. The data suggest that the active serum component exerts its inhibitory action at the cell surface. Since polymorphonuclear leukocytes are important mediators of inflammation and are implicated in the pathogenesis of tissue destruction, the subsidence of inflammatory diseases during gestation could be related, at least in part, to the inhibitory effects of pregnancy serum on leukocyte functions.