Electron microscope study of antigens in cells of mouse mammary tumor cell lines by peroxidase-labeled antibodies in sera of mammary tumor-bearing mice and of patients with breast cancer.

Sera of C3H/Z/Dm mice bearing spontaneous mam mary tumors, sera of apparently normal C3H/Z/Dm mice at different ages, and a serum of an A/Dm mouse with spontaneous breast cancer were tested by the indirect immunoperoxidase method against cells of C3H/HeJ spon taneous mammary tumor line constantly producing type B or mouse mammary tumor virus particles. The sera were also tested against cells of C3H/He/TEX spontane ous mammary tumor line producing no virus particles. Sera of C3H/Z/Dm and A/Dm tumor-bearing mice and serum of an apparently normal C3H/Z/Dm mouse gave peroxidase labeling of immature and mature type B or mouse mammary tumor virus particles and also of budding type B particles. No peroxidase labeling of intracytoplasmic type A virus particles was observed. In addition, peroxidase labeling of certain parts (presumably, antigen formation sites) of plasma membrane of the C3H/HeJ mammary tumor cells was seen. Absorption of the posi tive mouse sera with guinea pig kidney cells, C3H/Z/Dm mouse embryo cells, C3H/Z/Dm spontaneous mammary tumor cells, or with mammary tumor virus from milk of C3H/Z/Dm mice demonstrated that the immunoperoxidase reaction was due to specific antivirus antibodies. Positive sera failed to react with cells of the C3H/He/ TEX mammary tumor line producing no virus particles. A number of sera from patients with breast cancer and from their relatives were also tested by immunoperoxidase reaction against cells of the C3H/HeJ spontaneous mouse mammary tumor line. As in the case of positive mouse sera, some human sera gave peroxidase labeling of type B and budding virus particles. Absorption with suitable ma terial (guinea pig kidney, sheep red blood cells, whole hu man embryo cells, breast tumor tissue homogenates, and a mouse mammary tumor virus preparation) demon strated that the antibodies in human sera are specifically directed against mouse mammary tumor virus particles. INTRODUCTION