The effect of human pregnancy serum on the synthesis and action of interleukin-1.

Supernatants from mixed lymphocyte reactions performed in the presence of pregnancy serum (PS) or normal human serum (NHS) were tested for interleukin-1 (IL-1) activity in a thymocyte assay. A lower response was obtained with PS-containing supernatants, suggesting that PS exerts its suppressive effect by inhibiting IL-1 synthesis or by blocking its mode of action. IL-1 activity generated by human peripheral blood mononuclear cells (PBMC) stimulated with LPS and cultured in the presence of PS or NHS was similar. However, when PS was present, the proliferation of thymocytes co-mitogenically stimulated with PHA and exogenous IL-1 was diminished compared with the control (NHS), exhibiting its maximum inhibition when PS was added at the highest concentration and at the beginning of the incubation period. The suppressive effect of PS in the thymocyte assay disappeared with the combined action of exogenous IL-1 and IL-2. The response of T lymphocytes allogeneically stimulated was decreased in the presence of PS even when IL-1 was added; the recovery of proliferation being strictly dependent on the presence of the appropriate dose of exogenous IL-2. These results indicate that PS was interfering with IL-1 activity by rendering IL-2-producer cells unable to synthesize IL-2 and subsequently to proliferate.