(Auto)antibodies in human breast cancer sera against antigens associated with breast cancer cells, detected by immunoblotting

Sera of patients with breast cancer (as well as control normal sera and sera of patients with ovarian cancer or melanoma) were screened for the presence of antibodies against antigens expressed by the MDA breast cancer cell line. The techniques employed were radioimmunoassay with radioiodinated protein A and immunodotting with peroxidase-conjugated anti-human immunoglobulin antibodies. Sera reacting strongly by immunodotting were subsequently tested against antigens of the MDA and T47D cell lines in immunoblotting experiments. Both the breast cancer and the control sera yielded highly complex band patterns, which varied from serum to serum. The cancer sera differed from the normal sera, however, as they produced in most cases one or several bands that were distinctly stronger than the others. One of the strong bands, in fact a doublet of approximately 50 kilodaltons (kd), was produced preferentially (although not exclusively) when breast cancer sera were reacted with T47D cell membrane antigens. Absorption of selected sera with normal tissue or MDA antigens abolished or greatly reduced the intensity of some of the bands. It is concluded that, with the possible exception of the 50-kd band, most (probably all) of the bands seen in immunoblots resulted from the binding of autoantibodies to normal antigens expressed by the breast cancer cell lines. The main difference between cancer and normal sera would seem to be an increased content of autoantibodies in cancer, the specificity of these autoantibodies varying, however, from serum to serum.