Immunological studies of human placentae: the distribution and character of immunoglobulins in chorionic villi.

All four human IgG subclasses, and both kappa and lambda light chains, were detected by immunofluorescence in similar distributions in chorionic villi of human placentae. IgG1 and IgG3 were the predominant subclasses. No evidence was obtained for local enzymatic digestion of IgG during placental transfer. Most of the IgG on the trophoblastic basement membrane (TBM) was loosely bound and could be removed by prolonged washing, although some appeared to be more tightly bound to small segments of the TBM. IgM, but not IgA, was present in small amounts in placental villous structures. Immunoglobulin was never observed within the syncytiotrophoblast. Antisera to IgG genetic (Gm) markers were used to locate IgG thought to be of foetal or maternal origin. The presence of paternal Gm markers not carried by the mother was taken as evidence for foetal IgG. Foetal (paternal) Gm markers were observed in placentae, although maternal IgG was the major immunoglobulin present in placental villi. Both maternal and foetal IgG were demonstrated in fibrinoid deposits, vessel walls and the cytoplasm of some stromal cells. Only foetal IgG was definitively observed in the immunoglobulin that is tightly bound to the TBM.