Monoclonal Antibody against Rat Renal Cell Tumor‐associated Antigen as a New Tool for the Analysis of Renal Tumorigenesis

A monoclonal antibody, NR‐2 MAb, against one of the rat renal cell tumor‐associated antigens was developed. NR‐2 MAb belonged to IgM class and recognized a polypeptide of 81,000 daltons designated as NR‐2 antigen, which is of non‐glycoprotein nature with a pI of 4.6. NR‐2 MAb was employed to probe the histogenesis of renal cell tumors in rats treated with N‐ethyl‐N‐hydroxyethylnitrosamine followed by trisodium nitrilotriacetate monohydrate. Immunohistochemical analysis indicated that NR‐2 antigen was expressed in simple hyperplasia, adenomatous hyperplasia and renal cell tumors. Both clear cells and basophilic cells of the simple hyperplasia showed equally strong positive reactions with NR‐2 MAb, whereas the vacnolated epithelium was negative. Furthermore, the proximal tubules in nontumorous areas also expressed NR‐2 antigen, suggesting that the hyperplastic lesions which eventually lead to renal cell tumors may derive from cpithelia of proximal tubules and not directly from vacuolated epithelium. Such NR‐2 antigen‐positive epithelia of proximal tubules seem to be initiated cells. NR‐2 MAb also cross‐reacted with preneoplastic liver lesions.