Prevalence and distribution of murine mammary tumor virus antigen detectable by immunocytochemistry in spontaneous breast tumors of wild mice

Mouse mammary tumor virus (MuMTV) antigens were detected by immunoperoxldase cytochemistry In spontaneous breast tumors of wild mice from two widely separated areas of southern California. Eleven of 25 (44%) tumors from Lake Casltas (LC) mice and 4 of 5 tumors from Bouquet Canyon mice were positive. Included among the tumors lacking detectable MuMTV antigen were well-differentiated type A and type B carcinomas as well as tumors with an atypical pattern. In the antigen-positive tumors the distribution of staining was patchy and extremely variable in extent (`1-70% stained cells). The intensity and extent of staining were generally greater In breast tumors from hybrids of LC wild mice and C5LBL/10Sn or AKR inbred mice. A good correlation was found In the same tumors between immunoperoxldase staining, detection of MuMTV gp52 antigen by radioimmunoassay, and detection of type B particles by electron microscopy. All of the breast tumors in LC mice were positive for type C virus particles.