Immunocytochemical characterization of a monoclonal antibody directed against mitochondria reactive in paraffin-embedded sections.

The monoclonal antibody mES 13 was previously produced against bacterially expressed BALB ras p21 and was reported to have both membrane and cytoplasmic reactivity in formalin-fixed, paraffin-embedded tissue sections. In the current study, the cytoplasmic reactivity of mES 13 is investigated and demonstrated to be mitochondrial. Immunoelectron microscopic studies showed specific labeling of mitochondria without labeling of other organelles. In normal tissues, the antibody strongly labeled tissues known to have large amounts of mitochondria such as renal tubules, hepatocytes, and myocardium. The pattern of reactivity of tumors generally mimicked that of normal tissues, with carcinomas and melanomas usually showing stronger staining than sarcomas and lymphomas. Two granular cell tumors were negative. Among renal neoplasms, mES 13 strongly labeled renal oncocytomas and granular cell renal cell carcinomas and showed weaker staining of clear cell and chromophobe cell tumors. The mES 13 antibody should be useful in the characterization and diagnosis of tumors in which oncocytoma is in the differential diagnosis, especially when only paraffin-embedded tissue is available for study.