Human pregnancy serum inhibits interleukin-2 production.

Cell-mediated immunity may be depressed during pregnancy. We used the two way mixed lymphocyte reaction as an in vitro model of cell mediated immunity and studied the effect of pregnancy sera on this system by the amount of tritiated thymidine taken up by activated lymphocytes. We found that: (1) pregnancy sera contain a factor inhibiting the mixed lymphocyte reaction; (2) the inhibition of the mixed lymphocyte reaction induced by sera could be reversed by the addition of the supernatant from allogeneic mixed lymphocyte reaction; (3) pure interleukin-1 could not reverse the inhibitory effect and (4) recombinant interleukin-2 (IL-2) completely reversed the inhibitory effect of pregnancy sera on the mixed lymphocyte reaction. We conclude that a factor (or factors) present in serum from pregnant women is capable of inhibiting the generation of IL-2 during lymphocyte activation.