The objective of this project is to isolate and characterize major murine mammary tumor virus (MuMTV)-related antigens from the plasma membranes of the mouse mammary tumor cells and to elucidate the biochemical basis of the immunological cross-reactivity between the mouse mammary tumor and human breast carcinoma. The role of carbohydrates in the assembly, in biological properties of the mouse mammary tumor virion and in MuMTV-related antigens of the plasma membrane of mouse mammary tumor cells will be examined. Two mouse mammary cell lines, BALB/cf C3H and GR, grown in vivo and in vitro, will be used to produce MuMTV, mouse mammary tumor cells and solid tumors. The antigens of MuMTV isolated by ion exchange chromatography or affinity chromatography with plant lectins, gel filtration and/or preparative polyacrylamide gel electrophoresis in sodium dodecyl sulfate will be used to prepare monospecific antisera in rabbits. Indirect immunofluorescence and radioimmunoassay will be employed to determine the specificity of MuMTV-related antigens in mouse and human tumors and the specificity of antibodies, in the sera of patients with breast carcinoma, that are responsible for immunological cross-reactivity with MuMTV. Amino acid and carbohydrate analyses, determination of the molecular weight, pK of the protein and peptide maps will be performed to characterize the MuMTV-related antigens isolated from mouse and human tumors by affinity chromatography with immobilized antibody or physicochemical separation techniques.