Depression of cellular immunity in pregnancy due to a serum factor.

Lymphocytes from pregnant women and non-pregnant individuals were cultured under the stimulus of phytohaemagglutinin in the presence of their own and heterologous (allogeneic) sera. The results indicate that heterologous sera have an inhibitory effect on the lymphocyte transformation rate and suggest that the inhibitory property is more powerful in pregnant and fetal sera. Conversely, the addition of heterologous non-pregnant sera to cultures of pregnant lymphocytes increases their transformation rate. These findings suggest that there is a serum inhibitor in pregnancy and this finding may be relevant to the survival of the fetal allograft.