Further Characterization of the in Vitro Tumoricidal Activity of Staphylococcal Protein A

Treatment of plasma or serum from leukemic patients with solid phase staphylococcal Protein A induced leukemic blast cell lysis in vitro , but this effect was relatively independent of the amount of immunoglobulin G (IgG) removed. Samples with approximately equal cytotoxic activity contained markedly different IgG levels, while samples with similar IgG levels had a wide range of tumoricidal activity. Assays of plasma samples collected during a perfusion of one plasma volume through a Protein A-Sepharose column indicated that the duration of the procedure had a greater effect on cytotoxic activity than did the amount of IgG removed. Neither added leukemic nor normal IgG significantly improved blast cell viability in treated serum. Cytotoxic activity was not dialyzable and concentrated in the M r <100,000 fraction of samples separated by filtration. Treated cytotoxic serum samples did not have important C1q binding activity. These results suggest that the in vitro tumoricidal activity of solid phase Protein A is probably due to a toxic substance added to serum during immunoadsorption rather than to its immunoadsorptive capacity.