Expression of the human p55 and p75 tumor necrosis factor receptors in primary villous trophoblasts and their role in cytotoxic signal transduction

Tumor necrosis factor alpha (TNF alpha) induces the apoptotic death of primary villous cytotrophoblasts in culture (Yui et al., Placenta 1994; 15:819). Since both p55 and p75 TNF receptors (TNFRs) localize to the villous trophoblast, we examined their roles in mediating trophoblast apoptosis. Comparison of I-125-TNF alpha binding competition by receptor-specific antibodies revealed 2.7-fold more TNFRp75 than TNFRp55. Immunohistochemical analysis of receptor distribution showed TNFRp75 to be expressed strongly in < 20% of cells and TNFRp55 moderately in approximately 50%. Culture with TNF alpha increased the percentage of cells expressing TNFRp75 to > 40% but had little effect on TNFRp55 expression. Agonistic anti-TNFRp55 antibody and TNFRp55-specific TNF mutant protein stimulated both apoptosis and loss of trophoblast viability. In contrast, TNFRp75-specific mutant TNF alpha protein failed to induce either of these responses. Furthermore, neither cell death nor apoptosis stimulated by wild-type TNF alpha was inhibited by an antagonistic anti-TNFRp75 antibody. Thus, the apoptotic death of primary cytotrophoblasts is mediated almost entirely by TNFRp55, and the p75 receptor appears to have little effect on the process.