Inhibition of phytohaemagglutinin-induced lymphocyte blastogenesis by serum from pregnant women: correlation between cortisol level and in vitro immunosuppression.

Peripheral human blood lymphocytes stimulated by optimal doses of phytohaemagglutinin (PHA) were cultured in the presence of serum obtained from non-pregnant (controls) and pregnant women at different stages of gestation. A significant inhibitory influence on cellular growth was identified in the serum from pregnant women from the second trimester onward but more pronounced at the end of gestation. This inhibition was strongly correlated with the levels of cortisol in the sera. The action of commercial cortisol on lymphocyte reactivity in cultures stimulated by various concentrations of PHA and containing either a pool of pregnancy sera, or a pool of non-pregnancy sera, or a mixture of these pools was also investigated. The hormone provoked a significant inhibition more evident when low doses of PHA were used. The same finding occurred with the gravida's sera pool supplemented cultures.