Monoclonal antibodies were prepared against the Madin-Darby canine kidney (MDCK) cell line to identify epithelial cell surface macromolecules involved in renal function. Lymphocyte hybrids were generated by fusing P3U-1 myeloma cells with spleen cells from a C3H mouse immunized with MDCK cells. Hybridomas secreting anti-MDCK antibodies were obtained and clonal lines isolated in soft agarose. We are reporting on one hybridoma line that secretes a monoclonal antibody that binds to MDCK cells at levels 20-fold greater than background binding. Indirect immunofluorescence microscopy was utilized to study the distribution of antibody binding on MDCK cells and on frozen sections of dog kidney and several nonrenal tissues. In the kidney the fluorescence staining pattern demonstrates that the antibody recognizes an antigenic determinant that is expressed only on the epithelial cells of the thick ascending limb of Henle's loops and the distal convoluted tubule and appears to be localized on the basolateral plasma membrane. This antigen also has a unique distribution in non-renal tissues and can only be detected on cells known to be active in transepithelial ion movements. These results indicate the probable distal tubule origin of MDCK and suggest that the monoclonal antibody recognizes a cell surface antigen involved in physiological functions unique to the kidney distal tubule and transporting epithelia of nonrenal tissues.

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