Immunological cross reaction between sera from patients with breast cancer and mouse mammary tumor virus

Sera of Japanese women with breast cancer and without disorders of the mammary gland gave positive immunofluorescence reaction with mouse mammary tumor cells (MMT cells) producing type-A and type-B virus particles. Among these, 55.1% (49/89) of the sera from patients with breast cancer reacted with MMT cells, whereas 60% (3/5) of the sera from patients with benign mammary hyperplasia (2 of 3 mastopathies, 1 of 2 cystosarcoma phyllodes), 30% (12/40) of the patients with other than breast cancer (4 of 14 stomach cancers, 6 of 20 uterine cancers, 1 of 3 lung cancers, 1 of 3 rectum cancers), and 26.5% (18/68) of the sera from apparently healthy women showed positive reaction with MMT cells. Distribution pattern of the specific fluorescence obtained with positive human sera was similar to that resulting from the reaction with rabbit antiserum of type-A particles. Results of absorption studies and blocking tests also suggested that the reaction was due to the antigenic components common to type-A and -B particles. Furthermore, the results of membrane immunofluorescence tests suggested that some human sera also react with envelope antigen(s) of B particles. Antinuclear antibody was found in sera from 15.7% (14/89) of breast cancer patients by the indirect immunofluorescence tests, and antibody cross-reacting with mouse mammary tumor virus was not found in most of the sera from breast cancer patients who have antinuclear antibody.