Extracellular matrix components of the placental extravillous trophoblast: immunocytochemistry and ultrastructural distribution

Abstract

Invasive extravillous trophoblast cells of the human placenta are embedded in a self-secreted extracellular matrix, the matrix-type fibrinoid. The ultrastructure and molecular composition of the matrix-type fibrinoid of the term human placenta were studied by transmission electron microscopy and immunogold labelling. We used antibodies directed against different matrix proteins such as collagen type IV, laminin, vitronectin, heparan sulfate, various fibronectin isoforms, and against the oncofetal blood group antigen, "i". Immunogold labelling patterns of matrix proteins are the basis for the subdivision of the trophoblast-derived matrix-type fibrinoid into mosaic-like patches of structurally and immunocytochemically different compartments. Firstly, fine granular patches with structural similarities to basal lamina material are composed solely of collagen type IV and laminin. Secondly, an ultrastructurally amorphous glossy substance shows reactivity with antibodies against heparan sulfate and vitronectin. A third type of patches, fine fibrillar networks embedded in the above-mentioned glossy matrix, are reactive with antibodies against normal fibronectin isoforms (IST-4, IST-6, IST-9) and oncofetal isoforms (BC-1, FDC-6). The blood group precursor antigen "i" was not only expressed on the surfaces of the extravillous trophoblast cells but was associated with the fibronectin-positive fibrils. In conclusion, within this extracellular matrix, clear compartments of different composition can be distinguished from each other. Glycosylation with "i" in this matrix may be involved in immunological masking, thus preventing rejection of placenta and fetus.

Invasive depth of extravillous trophoblast correlates with cellular phenotype: a comparison of intra- and extrauterine implantation sites

“…They correspond to the former X-cells (for review see Benirschke and Kaufmann 2000). Their basement membrane-like ECM (called matrix-type fibrinoid; Frank et al 1994;Huppertz et al 1996) is composed of three different patches of matrix molecules: (a) collagen IV and laminin, (b) amorphous ground substance consisting of heparan sulphate and vitronectin and (c) fibronectins and fibrillin embedded in the same amorphous ground substance (Frank et al 1995;Huppertz et al 1996Huppertz et al , 1998King and Blankenship 1997). Interestingly, each individual cell of this type co-expresses different integrins in different membrane domains.…”

“…8B; Huppertz et al 1996), (b) heparan sulphate and vitronectin or (c) fibrillin and fibronectins (Fig. 8C) embedded in heparan sulphate and vitronectin (Huppertz et al , 1998King and Blankenship 1997).…”

“…The latter consists of a patchy pattern of laminins, collagen IV, vitronectin, heparan sulphate, cellular fibronectins including oncofetal isoforms and fibrillin (Frank et al 1994(Frank et al , 1995Huppertz et al 1996;Kaufmann et al 1996;King and Blankenship 1997). The EVT cells in this transitional zone are not thought to be really invasive.…”

“…In parallel, matrix composition changes to mostly fibronectins and fibrillin (Frank et al 1994(Frank et al , 1995Huppertz et al 1996;Kaufmann et al 1996;King and Blankenship 1997) and the integrin expression switches to predominance of α5β1, α1β1 and αvβ3/5 integrin, while α6β4 is no longer found (Damsky et al 1992(Damsky et al , 1994Irving and Lala 1995).…”

Adhesion Molecules in Human Trophoblast – A Review. II. Extravillous Trophoblast

“…Initially, within and nearby the cell columns, CTB interacts with a type of provisional ECM known as matrix-type fibrinoid (Figure 2a, b) that contains fibronectin [17], the ligand 50 for integrin α5β1, and vitronectin, which ligates αvβ3, as well as the basement membrane ligands laminin and collagen IV which bind α1β1. Fibrinoid accumulates between the cells and at the periphery of columns and probably anchors the columns to the maternal surface [18].…”