Murine mammary tumor virus expression during mammary tumorigenesis in ICRC mice.

The expression of murine mammary tumor virus (MuMTV) antigens was examined in the mammary epithelium of strains ICRC and C3H/Jax mice during sequential events leading to mammary tumorigenesis, employing immunoperoxidase technique and competition radioimmunoassays (RIA). The MuMTV antigens could be localized in the lobule alveolar structures of normal, lactating, preneoplastic and neoplastic mammary epithelium as well as in metastatic nodules of mammary tumors of ICRC force breeders. A graded increase in staining reaction was evident with increase in cellularity of the mammary gland due to age and parity. These observations compared well with the quantitation of MuMTV antigens by RIA. The levels of MuMTV antigens in the mammary glands of ICRC mice of different experimental groups were consistently lower than those in C3H/Jax mice. The differential response of the mammary glands to ovariectomy observed in these two strains was reflected in the MuMTV expression.