A microassay for antibody binding to tumor cell surface antigens using 125I-labelled protein a from Staphylococcus aureus.

A sensitive assay for antibodies bound to the surface antigens of adherent tumor cells using protein A from Staphylococcus aureus is described. Cells, as monolayers in microtest wells, are incubated first with immune or control serum, and then with 125I-labelled protein A (IPA), which binds to IgG antibodies bound to cell surface antigens. The IPA assay is shown to be more sensitive than the conventional isotopic antiglobulin (IAG) assay, because IPA binds to a lesser extent to IgG bound non-specifically to cells.