Ultrastructural localization by monoclonal antibodies of brush border antigens expressed by glomeruli. II. Extrarenal distribution.

An immunoultrastructural study has been undertaken for analysis of the extrarenal localization of two brush border (BB) glycoproteins of 90 kd and 330 kd expressed by glomeruli. In previous studies on renal tissue, it has been shown that gp 330 is restricted to coated pits and BB intermicrovillar invaginations, whereas gp 90 is diffusely distributed on epithelial cell membranes and in addition expressed on glomerular endothelial cells. At variance from observations made in the kidney, gp 330 and gp 90 are mainly expressed on different epithelial cell types: gp 330 is found on the coated pits of the epithelium lining the epididymis and on the entire surface of the microvilli of Type II pneumocytes, whereas gp 90 is detected on the gut brush border and the biliary pole of hepatocytes; gp 90 is also found on endothelia lining all distal capillary beds studied in heart, lung, liver, and spleen. These observations thus indicate that gp 90 is expressed by a wide variety of cell types, all associated with high membrane turnover. Conversely, gp 330 has a restricted distribution at the organ, cellular and subcellular level and may be related with a defined system of receptor-mediated endocytosis.