Immunological studies of human placentae: complement components in immature and mature chorionic villi.

The localization and distribution of complement components in term and pre-term normal human placentae have been studied by using haemadsorption and immunofluorescence experiments. The components Clq, C4, C5, C6 and C9 were identified in characteristic locations. Receptors for C3 and C4 were not found. Complement was associated with certain stromal cells, areas of fibrinoid necrosis within the trophoblastic mantle, and in the walls and endothelia of foetal stem vessels. Activation of the complement system on trophoblastic basement membranes (TBM) did not appear to involve the early reacting components of the classical pathway of complement activation, because C1q, C4 and C2 could not be identified on TBM. The C6 component was identified within cytoplasmic granules of foetal stem vessel endothelia, suggesting that it may be synthesized by these cells. These findings put forward the possibility that complement may play an immunobiological role in the materno-foetal relationship during normal human pregnancy.