Anchoring villi in human placental basal plate: lymphocytes, macrophages and coagulation

We have studied basal plates in 25 normal placentae, ten placentae from primary aborters and six placentae from secondary aborters for leukocyte markers and coagulation components. Anchoring villi contained class II MHC antigen-reactive (HLA-DR, DP and DQ) macrophages and T-lymphocytes of the helper (CD4) phenotype. Antibodies to coagulation components revealed the presence of tissue factor, factor IX and fibrin in and around anchoring villi. Immune cells and coagulation components in anchoring villi were more frequently identified in secondary aborters. These findings provide morphological support for an idea that there is a linkage between the presence of immune cells and coagulation in anchoring villi of the basal plate. Helper T-lymphocytes can activate macrophages which release cytokines that activate coagulation through the extrinsic pathway. We envision this as an expression of maternal allogeneic recognition of extraembryonic tissues in the basal plate.