Demonstration of the ability of Hofbauer cells to phagocytose exogenous antibodies.

We have studied the effects of the anti-human chorionic gonadotropin and anti-human antithrombin III antibodies on Hofbauer cells from human immature placenta, when applied to either intact villi or on cell culture. Trypsin treatment of the villi results in a mixed cell culture mainly composed of isolated Hofbauer cells but which also contains a variable number of mesenchymal cells and a few syncytiotrophoblastic cells. In all samples analysed only 7-8% of the Hofbauer cells and some syncytiotrophoblastic cells exhibited a macrophagic activity 24 h after incubation of the cultures with the antisera. That only certain proportions of Hofbauer and syncytiotrophoblastic cells express macrophagic activity is also seen when intact villi are incubated for 24 h with these antibodies. Indeed, neither all the villi nor all these cells within a single villus are positively stained. The fact that only a fraction of Hofbauer cells and syncytiotrophoblast express a macrophagic activity may suggest that only some cells, amongst both these cell types, are involved in the protection of the fetus against maternal immunological rejection by removing immunological complexes.