Characterization of Raji cell binding IgG in patients with metastatic breast cancer.

The aim of the present study was to isolate and characterize the immune complexes detected by the Raji cell assay in metastatic breast cancer. However, the Raji cell binding material could not be separated from monomeric IgG by Sephacryl S-300 gel chromatography in any of the 16 sera investigated. The parallel elution profile of monomeric IgG and the Raji cell binding activity suggested that anti-Raji cell antibodies, rather than immune complexes of low molecular weight, were present in these sera. This was further substantiated by pepsin digestion of the Raji cell binding IgG fractions. The binding of F(ab')2 fragments was quantitatively comparable to the binding of undigested IgG, and the bound F(ab')2 fragments could be visualized by immunofluorescence at the cell membrane. The presence of antibodies against Raji cells was further confirmed by the complement-dependent cytotoxicity assay. These antibodies did not react with untransformed lymphocytes and there was no correlation with anti-Epstein-Barr virus antibodies. The incidence of cytotoxic anti-Raji cell antibodies in breast cancer was 12% compared to 20% in malignant lymphoma, to 0% in normals and patients with degenerative cardiovascular diseases, and to 5% in patients with auto-immune diseases.