Effect of pregnancy plasma upon in vitro parameters of cell mediated immunity

Pregnant women were classified according to their serological status for cytomegalovirus, herpes simplex virus or rubella virus. Lymphocytes taken from non-pregnant women were shown to be able to recognise viral antigens and the mitogen phytohaemagglutinin by the measurement of proliferative responses and by the production of gamma interferon. Proliferative responses or gamma interferon production were greatly reduced in the presence of plasma taken during the first, second or third trimester and immediately post-partum. The responses then gradually returned to normal after delivery. The availability of serial sera taken before pregnancy as well as during and after pregnancy in individual women showed that this effect was maintained even when sera had been stored frozen for more than one year. Mixing experiments were performed to vary the proportion of pregnancy serum in any particular assay but this did not prove that pregnancy sera were actively suppressive. Instead, the data suggest that pregnancy sera are deficient in some factor or factors which are required to support lymphocyte proliferation. The effect was not attributable to the physiological haemodilution of pregnancy leading to a reduced concentration of putative factors nor could transferrin levels or the iron binding capacity of this protein be implicated.