ANTIADHESIVE GLYCOSYLATION OF FIBRONECTIN-LIKE MOLECULES IN HUMAN PLACENTAL MATRIX-TYPE FIBRINOID

Recently, fibrinoid of the human placenta has been described as being composed of two main types differing in origin and chemical compositio n. Fibrin-type fibrinoid is mostly a blood clot product. Matrix-type f ibrinoid was defined as the extracellular matrix secreted by extravill ous trophoblast cells. The structure and composition of matrix-type fi brinoid was addressed in this study, focusing on fibronectins as one m ajor constituent. A pan el of antibodies directed against different fi bronectin isoforms generated by different mRNA splicing, as well as an tibodies recognizing oncofetal carbohydrate epitopes, were used on cry ostat, paraffin and Lowicryl sections of placental tissue from differe nt stages of pregnancy. The oncofetal carbohydrate epitopes studied co mprised the blood group precursor antigens i and I. We identified the blood group-related antigen i as an additional marker for matrix-type fibrinoid. The antigen was detected on a glycoprotein that was also re cognized by the fibronectin antibodies in western blots. Immunohistoch emically this i-glycosylated oncofetal fibronectin-like molecule of ab out 55 kDa is expressed only by the invasive phenotype of extravillous trophoblast. Long chain carbohydrate moieties with a structure fulfil ling the criteria for i reactivity on human placental fibronectin are known to have antiadhesive properties and to enhance resistance of the protein chain to proteolysis. These properties underline the function al relevance of glycosylation of fibronectins in matrix-type fibrinoid and suggest matrix-type fibrinoid is a typical matrix of invasive cel ls. In contrast, the more mature blood group precursor I could be dete cted after sialidase pretreatment of sections. This antigen was expres sed by villous, non-invasive trophoblast.