• Immunosuppressor factor;
  • immunohistochemistry;
  • trophoblast;
  • embryo

PROBLEM: To study whether embryo associated immunosuppressor factor (EASF) is synthesized at the maternal-fetal interface.

METHOD: Anti-EASF monoclonal antibody H5D12 was used to identify EASF. Paraffin-embedded sections were prepared from placental and fetal tissues and immunohistochemistry was done by the avidin-biotin-peroxidase technique. EASF was affinity purified using H5D12-Sepharose 4B from culture media of placental villi and analyzed for immunosuppressive activity (by Concanavalin A-induced lymphocyte proliferation assay) and molecular weight identity (by metabolic labeling studies with 35S-methionine followed by immunoprecipitation and SDS-PAGE).

RESULTS: Immunohistochemical studies demonstrates intense immunostaining of villous syncytiotrophoblast and cytotrophoblast cells of first trimester placental tissues. Hoffbauer cells and decidual cells stained positive. The same cells in second and third trimester placental tissues stained weakly. However, the endothelium and smooth muscle cells of fetal blood vessels, fetal ovarian stroma and primordial follicles, kidney epithelium, cerebral neurons, and glial cells all stained negative. The affinity-purified EASF from the conditioned media of placental villi (less than 12 wk gestational age) was identified as a 37-kDa molecule with immunosuppressive activity. Metabolic labeling studies revealed that placental villi from early gestational age secretes a major factor of 37-kDa and minor factors of 41-kDa and 47-kDa molecular weight.

CONCLUSIONS: Monoclonal antibody H5D12 identifies a factor that is produced by the pre-implantation embryo and also synthesized by decidua and trophoblast cells.