THE EXPRESSION OF A PROGESTERONE-INDUCED IMMUNOMODULATORY PROTEIN IN PREGNANCY LYMPHOCYTES

PROBLEM: The immunological effects of progesterone are mediated by a p rotein, named the progesterone-induced blocking factor (PIBF). The PIB F blocks NK activity in vitro and therefore prevents the abortive effe ct of high NK activity in mice. Increased NK activity has been suggest ed to play a role in pregnancy termination; thus NK inhibitory effect of the PIBF should contribute to the maintenance of normal gestation. This study was designed to investigate the relationship between in viv o PIBF-producing capacity and in vitro cytotoxic activity of pregnancy lymphocytes, as well as the clinical status or the outcome of pregnan cy. METHOD: Lymphocytes of 168 pregnant women (96 normal pregnancies, 16 showing clinical symptoms of threatened preterm pregnancy terminati on, 46 recurrent aborters, and 10 women sampled at the onset of sponta neous abortion or preterm delivery) were isolated on Ficoll-Paque grad ient. The lymphocytes were tested for reactivity with a PIBF-specific antibody by immunocytochemistry, and simultaneously for cytotoxic acti vity to human embryonic fibroblast targets. RESULTS: The percentage of PIBF-positive lymphocytes in peripheral blood of healthy pregnant wom en was significantly higher than in that of women at risk for prematur e pregnancy termination. In peripheral blood of patients undergoing sp ontaneous pregnancy termination at the time of sampling, and in those of women showing symptoms of premature pregnancy termination we found lower than normal percentage of PIBF-positive cells. PIBF expression o f the lymphocytes showed an inverse correlation with NK activity, and the rate of PIBF positive lymphocytes was related to the outcome of pr egnancy. CONCLUSION: These data suggest a strong relationship between PIBF producing capacity as well as NK activity of the lymphocytes and the success of gestation.