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Antibodies to the 280-kd coated pit protein, target of teratogenic antibodies, produce alterations in the traffic of internalized proteins.

Previous studies have identified two high-molecular weight (280 and 330 kd) glycoproteins expressed by coated pits of the proximal renal tubule and yolk sac and have further established that, in vivo, antibodies to gp280 but not to gp330 induce fetal malformations. In the present study, we report the effect of these antibodies on the endocytic process by yolk sac visceral epithelial cells of rat embryos explanted at day 10 of gestation. Antibodies to gp280 markedly altered development of the yolk sac and embryo, induced malformations, inhibited by 40% the uptake of [14C] sucrose and perturbed the intracellular traffic of internalized proteins. Under control conditions, rat immunoglobulin G present in the culture medium was immunolocalized in lysosomes of epithelial cells, whereas in the presence of antibody, it was detected in small vesicles scattered through the apical cytoplasm. Alterations of the endocytic pathway were confirmed by experiments analyzing the uptake of peroxidase added to the medium for 2 to 60 minutes. The initial compartments of endocytosis visualized by peroxidase were increased in size and abnormal in shape and the transfer of the internalized peroxidase to the lysosomal compartment was delayed. In contrast, antibodies to gp330 had a minimal effect on embryonic development and did not induce fetal malformations. Endocytosis was only modestly altered; uptake of [14C] sucrose was decreased by 25%, and only minor modifications of the intracellular transit of peroxidase could be detected. We suggest that the key role of anti-gp280 antibodies is via trapping of the target antigen in the early endocytic compartment thus preventing its normal function in lysosomal transfer.