Rat Heymann nephritis antigen is closely related to brushin, a glycoprotein present in early mouse embryo epithelia

Abstract

Heymann nephritis is a glomerulonephritis induced in rat by injecting kidney extracts. The responsible antigen is known to consist of two high molecular weight glycoproteins, gp330 and gp300, located in renal tubular brush border cells. We show that rabbit antibodies made against purified rat gp330 react in immunofluorescence tests with several polarized epithelia present in pre- and post-implantation mouse embryos, as well as with murine trophoblastoma cells. Immunoprecipitation experiments demonstrate that anti-gp330 antibodies also recognize two components with relative molecular weights of 330 and 300 Kd in mouse embryonic cells. Furthermore, sequential immunoprecipitation experiments and limited proteolysis tests suggest that these two components are identical with brushin, a glycoprotein set known to be present in a mouse early embryonic epithelium and in adult kidney cells. Finally, ultrastructural studies demonstrate that anti-gp330 antibodies react with molecules preferentially located in coated pits of murine early epithelial cells. These results show that Heymann nephritis antigen has an embryonic counterpart closely related to, if not identical with, previously identified brushin glycoproteins. These molecules could be a receptor to an unknown ligand or a structural component of coated pit membrane.