Immunohistochemical localization of extracellular matrix in perivillous fibrinoid of normal human term placenta

The extracellular matrix of perivillous fibrinoid in normal human term placenta was investigated by means of the indirect immunofluorescent technique. Polyclonal antibodies to collagen types I, III, IV, V, fibronectin, fibrinogen, laminin, entactin and heparan sulphate proteoglycan and monoclonal antibodies BC-1, IST-9 and IST-4 to human fibronectin were used. The antigens can be grouped according to their presence in fibrinoid as abundant (fibrinogen, fibronectin, heparan sulphate proteoglycan, basement membrane collagen types IV and V), absent (laminin) and variable between fibrinoids (interstitial collagen types I and III, entactin). Our results also demonstrate that fibronectin in fibrinoid originates from placental cells (presumably cytotrophoblast). Monoclonal antibodies BC-1 and IST-9 specific to tissue fibronectin do not stain neighbouring placental extracellular matrix but do bind to fibrinoids on the same sections. Work by other authors has presented evidence that fibrin actually originates from maternal blood and even makes an attempt to substitute the term “fibrinoid” for “fibrin deposition”. Our data on the composition of perivillous fibrinoids and the abundance of extracellular matrix components do not support this view and suggest that fibrinoid is a more relevant term for this interesting phenomenon, which deserves further investigation.