Immunological studies of human placentae: identification and distribution of proteins in immature chorionic villi

Cryostat sections of normal human first-trimester placentae have been studied by indirect immunofluorescence to localize numerous protein antigens to well-defined anatomical regions. Transferrin was identified in the apical aspect of all trophoblasts. Fibrinogen/fibrin was also clearly demonstrated in speckled pattern in this location and similar reactions were also observed for alpha-2-macroglobulin, IgG and C3. Plasminogen was identifiable in trophoblasts, and beta-2-microglobulin was uniformly absent from these cells. Collagen and fibrinogen/fibrin were demonstrated on trophoblastic basement membrane, whereas IgG and C3 were only very rarely identified at this site. Few antisera gave strong staining of first-trimester villous stroma, although collagen was shown to contribute much of the stromal matrix. Fibrinogen/fibrin, plasminogen, alpha-2-macroglobulin, C4, C3, C1q, IgG and caeruloplasmin gave positive reactions in fibrin and fibrinoid areas, and phytohaemagglutinin was demonstrated to bind strongly to these areas as well as to trophoblastic basement membrane.