Perforin-like immunoreactivity in four cases of lymphoma of large granular lymphocytes in the cat.

Tumors composed of discrete round cells with large eosinophilic granules in their cytoplasm were observed in four cats. These cats were presented with severe gastrointestinal signs, including anorexia, vomiting, and diarrhea. The exploratory laparotomy in two cats and necropsy in the other two revealed thickening and perforation of the intestinal walls, enlargement of the mesenteric, ileocolic, and/or colic lymph nodes, and splenomegaly. Histologically, there was severe and disseminated infiltration of the tumor cells in the affected organs. In the two cats necropsied, the spleen and the jejunal mucosa appeared to be the primary organs involved. The tumor cells of all the cats showed the pore-forming protein (perforin)-like immunoreactivity unique to the cytotoxic lymphocytes but failed to show histamine immunoreactivity. These results indicate that the tumor cells were derived from large granular lymphocytes and that perforinlike immunoreactivity may be a useful marker for histologic diagnosis of feline large granular lymphoma.