Placental isoferritin as a physiological downregulator of cellular immunoreactivity during pregnancy.

CM-H-9 monoclonal antibody specific for placental isoferritin (PLF) was used to quantify PLF in the serum and on peripheral blood lymphocytes derived from term delivery women and healthy controls. It was found that the mean level of PLF in maternal sera was 50.4 +/- 50.1 U/ml, whereas in normal adults the mean serum PLF level was very low (4.5 +/- 7.7 U/ml). Furthermore, term mothers exhibited a sub-population of peripheral blood lymphocytes (PBL) which stained positively with CM-H-9 MoAb (mean 11.6 +/- 7.8%). Such lymphocytes were scarce in normal non-pregnant women (mean 0.8 +/- 1.2%). The effect of PLF on lymphocyte transformation in MLC was studied in mixed lymphocyte cultures of maternal-newborn and normal non-related PBL controls. It was found that placental isoferritin was immunosuppressive in comparison to normal adult ferritin. The suppressive effect was significantly higher in maternal-newborn MLC compared to normal adult controls. Furthermore, it was found that PLF which is present in maternal serum has an immunosuppressive activity since, its removal on CM-H-9 MoAb affinity column abrogated this effect. The results of this study suggest that both PLF and PLF binding lymphocytes play a role in the development of immunosuppression during pregnancy. Therefore the lack of one of the factors may result in diminished immunosuppression or in fetal rejection.