Human pregnancy serum suppresses the proliferative response of lymphocytes to autologous PHA-activated T lymphoblasts.

PROBLEM

We have previously demonstrated that human serum can suppress the proliferative response in autologous mixed lymphocyte reaction (AMLR) in which phytohemagglutinin (PHA)-activated T lymphoblasts act as stimulators (T-TPHA AMLR). The aim of the present work was to determine whether pregnancy serum (PS) possesses an inhibitory capacity similar or different in magnitude.

METHODS

Sixteen PS were added to T-TPHA AMLR cultures and the proliferative response was compared with that in the presence of human serum. The effect of PS on the IL-2 dependent proliferation of PHA-activated T Lymphoblasts was examined as well.

RESULTS

PS induced a significantly more pronounced suppression of T-TPHA AMLR than human serum (P < 0.05). One PS tested was not inhibitory but rather stimulatory. This PS was obtained from a woman who subsequently had IUGR. The inhibition is related to the existence of a serum inhibitory factor and not to the lack of a serum supporting factor. PS inhibited not only T-TPHA AMLR of the same woman but also T-TPHA AMLR of other individuals as well, implying that the inhibitor is a non-MHC restricted factor. IL-2 dependent cell proliferation was not inhibited by PS, implying that the inhibitor detected in T-TPHA AMLR is not a general cell proliferation inhibitor.

CONCLUSIONS

These results suggest that a non-MHC restricted inhibitory factor present in PS may play an important biological role in regulating local immune responses in the fetal-placental unit mediated by autoreactive T cells restricted to autologous activated T lymphocytes.