Renal cell tumours in mice: electron microscopy versus immunohistochemistry

15 renal cell tumours induced in CBA male mice by 1,2-dimethylhydrazine were studied electronmicroscopically (EM). All these tumours earlier were investigated histochemically and immunohistochemically with the use of gamma-glutamyltranspeptidase (GGT) as a marker of the proximal tubules and antigen A6 as a marker of distal tubules and/or collecting ducts. One of the tumours was GGT-positive and antigen A6-negative and ultrastructurally well developed brush border was found. This correlation between immunohistochemistry and EM data allowed to conclude that the site of origin of this tumour were the cells of the proximal tubules. All other tumours were GGT-negative and antigen A6-positive, i.e. the development of these tumours from the distal tubules (and not from the proximal tubules) could be suspected. However in 5 of these neoplasms reduced brush border was found. Microvilli were of a smaller size than in normal proximal tubules and were frequently located not on the apical cell surface but in the narrow spaces between two cells. Invaginations and apical vesicles typical for the normal proximal tubules were also found in some tumour cells. EM and immunohistochemical data combined allow to suggest the origin of these tumours from the common precursor cell capable of differentiation, in the course of tumour progression, into the cells with properties of proximal and/or distal tubules.