| Abstract: | Antibodies specific for bovine ribonuclease A (antiRNase A) were raised in rabbits, and immunologic cross-reactivity between bovine RNase A and human salivary gland RNase was demonstrated. The antiRNase A served as the primary antibody in the peroxidase-antiperoxidase immunohistochemical technique. Paraffin blocks of five normal human parotids and 20 parotid tumors were examined. In normal parotid and in cases of cystadenoma lymphomatosum, immunoreactive RNase was localized in the ductal epithelium, evidence of the ductal cell origin of these benign tumors. RNase immunoreactivity was noted in the adenomatous structures and in cells isolated in the myxoid matrix of pleomorphic adenomas, which supports recent evidence of an epithelial origin of these tumors. Malignant acinar cells of acinic cell carcinoma were strongly positive for immunoreactive RNase, while acinar cells of normal parotid were uniformly negative. This expression of the gene for RNase A probably represents a loss of differentiation (i.e., control) of the neoplastic acinar cells. Further evidence for this hypothesis was obtained by treating these tumors with an antihuman salivary amylase antibody, which is localized in normal acinar cells. No immunoreactive amylase was observed. The results support the idea that immunoreactivity need not accompany enzyme activity, as the presence of immunoreactive RNase was noted in all neoplastic tissues examined. Immunohistochemical localization of two antigens in the same tissue demonstrates the varied biochemical changes associated with parotid neoplasia. |
