INHIBITORY EFFECT OF CHORIOCARCINOMA-DERIVED HIGH-MOLECULAR-WEIGHT FACTOR (HMWF) ON LYMPHOCYTE-PROLIFERATION AND ADHESION TO TROPHOBLASTS

Trophoblast-secreted soluble factors may deter the immune rejection of the fetus which can occur from interaction between maternal lymphocytes and fetal trophoblasts in decidua. The effect of size-fractionated culture fluid of choriocarcinoma cells on the function of lymphocytic cells was studied. The results show that dialyzed soluble factor (HMWF) of molecular weight > 100 kDa was inhibitory to lymphocyte proliferation in a dose-dependent manner and prevented lymphocyte-to-trophoblast adhesion in a similar fashion. The effect was abrogated by a freezing-thawing process and heat treatment. Similarly, the fractions below 100 kDa size had no effect on lymphocyte functions. Although the nature of HMWF is not yet known, it appears that this factor differs from most of the well-characterized pregnancy factors but is similar to the recently described high molecular weight factor found in primary cultures of trophoblasts and choriocarcinoma lines. The inhibitory effect of trophoblast-derived HMWF on cell-contact-based immune recognition may contribute to maternal tolerance.