Altered humoral immunoregulation during human pregnancy

The in vitro production of immunoglobulins in response to stimulation with pokeweed mitogen (PWM) and fixed/killed Staphylococcus aureus Cowan 1 (SAC) was measured in conjunction with in vivo assays of plasma immunoglobulin levels to examine the quality and quantity of humoral immunity during human pregnancy and at parturition. Following stimulation with PWM, there is a significant enhancement of in vitro immunoglobulin-G (IgG) production during pregnancy. Following stimulation with PWM and SAC, there was a significant reduction in in vitro immunoglobulin-M (IgM) production immediately following parturition. There was a significant decrease in the plasma levels of IgG during pregnancy, although no change in the plasma levels of IgM were observed. The decrease in plasma immunoglobulin levels during pregnancy cannot be explained as the result of hemodilution and transplacental transfer. Altered humoral immunoregulation is the most likely means whereby an increase in immunoglobulin production during human pregnancy could occur. The possible effects of this on the outcome of pregnancy are discussed.