ANTIGEN EXPRESSION IN NORMAL AND NEOPLASTIC CANINE TISSUES DEFINED BYA MONOCLONAL-ANTIBODY GENERATED AGAINST CANINE MESOTHELIOMA CELLS

Monoclonal antibody (MAb) 3B5 generated against canine mesothelioma ce lls was applied to canine tumors and normal tissues via immunohistoche mical and immunoblotting techniques to evaluate antigen binding. By us e of an avidin-biotin immunoperoxidase complex (ABC) method, immunorea ctivity was noted in reactive mesothelial cells and in normal tissues was observed primarily in mesothelial cell linings, endothelial cells, and smooth muscle of blood vessels and soft tissues; the reactivity w as nearly equivalent in frozen or formalin-fixed, paraffin-embedded ti ssue sections. Use of the ABC method on formalin-fixed, paraffin-embed ded tumors yielded moderate to strong cytoplasmic immunostaining of ne oplastic cells in 10/11 (91%) mesotheliomas, 18/23 (78%) hemangiosarco mas, 4/10 (40%) intestinal and lung carcinomas, and less than or equal to 20% of hemangiomas, leiomyosarcomas, leiomyomas, mammary carcinoma s, and squamous cell carcinomas. No immunostaining of tumor cells was observed in fibrosarcomas, hemangiopericytomas, perianal gland carcino mas, and melanomas. Immunoblotting was performed on samples that demon strated strong immunoreactivity with MAb 3B5 by the ABC method: mesoth elioma, hemangiosarcoma, urinary bladder (smooth muscle), and lung (al veolar capillaries). These analyses showed that MAb 3B5 bound a major antigen of 78 kilodaltons (kd) and minor antigens at 56 and 54 kd in n ormal and neoplastic tissues. The preliminary immunohistochemical resu lts suggest that MAb 3B5 may possess utility in diagnosis of mesotheli omas and hemangiosarcomas, discrimination of cell types in proliferati ve serosal lesions, and demonstration of vascularity or angiogenesis i n neoplastic and inflammatory lesions.