Monoclonal antibodies against luminal membranes of renal proximal tubules which are kidney-specific

After immunization with porcine brush-border membrane proteins, 11 monoclonal antibodies were generated which react with proximal tubules. Their antigenic polypeptides were characterized with respect to apparent molecular weight, histochemical localization in porcine and human kidney, and tissue distribution in pig. In porcine kidney, six antibodies bind selectively to the proximal tubule whereas the others also react with other nephron segments. With the exception of one antibody which reacts with the luminal and the basolateral membrane of the porcine proximal tubule, the other antibodies specific for the proximal tubule only stain the brush-border membrane. Four of them react along the entire length of the porcine proximal tubule, whereas one (R1A2) binds to the S3-segment in pig and to the entire length of the proximal tubule in man. This indicates that segment-specific expression may be species-dependent. Testing the antibodies in 21 different extrarenal tissues it was found that three of the antibodies, specific for the brush-border membrane in renal proximal tubules, only react in kidney. Two of these are specific for pig kidney whereas one also reacts with human kidney. This antibody (N4A4) is directed against a polypeptide with an apparent molecular weight of 400,000. Electron microscopic immunohistochemistry showed that N4A4 binds to the intervillus region of the brush-border membrane and to subapical vesicles.