Immunohistochemical study of porcine nephroblastoma.

Nephroblastoma, a relatively common renal neoplasm of young swine, represents the animal counterpart of Wilms' tumour of children. Five porcine nephroblastomas were examined histologically, and immunohistochemically with antibodies against vimentin (VIM), cytokeratins (CKs), smooth-muscle actin, Factor VIII, and laminin. Histologically all showed the three components typical of this tumour: mesenchymal blastema, epithelium (tubuli, and glomeruloid bodies) and stroma. The only antibody recognizing mesenchymal cells was VIM. One-third of tubular structures were positive for VIM. All of the tubules were positive for CK19, two-thirds expressed CK AE1/AE3, and only one-third expressed CKs 8-18. Small round tubuli, located in the stromal septa, were positive for CK7 (ureteric branches). Stromal cells expressed both VIM and actin, demonstrating myofibroblastic differentiation. The kidney originates from mesenchymal blastema, which changes to epithelium, losing VIM and acquiring CK expression. In the adult mammalian kidney, CK 19 is expressed only by the parietal epithelium of Bowman's capsule and the distal tubules. Nevertheless, CK19 is also considered a "transient" CK, expressed by different kinds of epithelia during differentiation. CK 19 was also detected in several undifferentiated neoplasms. This finding, together with the co-expression of VIM detected in some tubules, demonstrates the embryonic origin of nephroblastoma.