LYSOZYME-CONTAINING RENAL TUBULAR HYALINE DROPLETS IN F344 RATS BEARING A RAT FIBROSARCOMA-DERIVED TRANSPLANTABLE TUMOR

Renal tubular hyaline droplets developed in male and female F344 rats bearing a rat fibrosarcoma-derived transplantable tumor (SS). The drop lets accumulated exclusively in the proximal renal tubular epithelia a s eosinophilic granules of various sizes in hematoxylin and eosin-stai ned sections. The granules stained bright red with azan-Mallory stain. Immunohistochemically, the droplets were positive for lysozyme to var ious degrees but were negative for alpha 2u-globulin, albumin, and alp ha 1-antitrypsin. These findings indicated the involvement of lysozyme , a low-molecular-weight protein, in the droplet formation. The morpho logical and immunohistochemical findings of the hyaline droplets bore a close resemblance to those reported in rats as a secondary lesion to spontaneous histiocytic sarcomas. Others have speculated that renal t ubular hyaline droplets in histiocytic sarcoma-bearing rats are formed in lysosomes through cellular overload of lysozyme secreted excessive ly by the tumor cells. However, neoplastic cells of SS tumors were neg ative to lysozyme. The pathogenesis of renal hyaline droplets appearin g in SS tumor-bearing rats remains to be investigated.