MONOCLONAL-ANTIBODIES AGAINST LUMINAL MEMBRANES OF RENAL PROXIMAL TUBULES WHICH ARE KIDNEY-SPECIFIC

After immunization with porcine brush-border membrane proteins, 11 mon oclonal antibodies were generated which react with proximal tubules. T heir antigenic polypeptides were characterized with respect to apparen t molecular weight, histochemical localization in porcine and human ki dney, and tissue distribution in pig. In porcine kidney, six antibodie s bind selectively to the proximal tubule whereas the others also reac t with other nephron segments. With the exception of one antibody whic h 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 en tire length of the porcine proximal tubule, whereas one (R1A2) binds t o the S3-segment in pig and to the entire length of the proximal tubul e in man. This indicates that segment-specific expression may be speci es-dependent. Testing the antibodies in 21 different extrarenal tissue s it was found that three of the antibodies, specific for the brush-bo rder membrane in renal proximal tubules, only react in kidney. Two of these are specific for pig kidney whereas one also reacts with human k idney. This antibody (N4A4) is directed against a polypeptide with an apparent molecular weight of 400000. Electron microscopic immunohistoc hemistry showed that N4A4 binds to the intervillus region of the brush -border membrane and to subapical vesicles.