Immunohistological characterization of lymphoid cell populations in the early human placental bed.

The distribution of leukocytes in first trimester human decidual tissue has been studied by using a panel of monoclonal antibodies in an indirect immunoperoxidase technique on acetone-fixed cryostat sections. The results indicate that bone marrow-derived cells are abundant in the placental bed and a proportion of these are HLA-DR positive. However, a major leukocyte population in the decidua of early pregnancy is of cells which carry the E-rosette receptor but which do not express peripheral pan-T cell antigens nor HLA-DR. The distribution of these cells suggests that they are endometrial granulocytes. A similar large number of cells express OKT 10, a marker of immature or activated cells. The presence of this unusual T lineage cell raises the possibility that a form of lymphocyte processing is occurring in the decidua in early pregnancy, perhaps in response to foetal antigens presented on trophoblast.