Immune complexes and circulating antibodies against autologous leukaemic cells in patients with acute leukaemias.

Serum of patients with different forms of acute leukaemias were analysed either for the presence of circulating antibodies against autologous leukaemic cells or for that of soluble immune complexes. At the moment of their diagnosis, twelve of twenty-five patients with different types of leukaemias, showed circulating serum immunoglobulins capable of binding to the leukaemic cell surface (LCS). These anti-LCS immunoglobulins were of the IgG class and were detectable by a binding assay employing glutaraldehyde-fixed target cells and radioiodinated Staphylococcus aureus Protein A. Their digestion with pepsin showed that the site involved in the binding was in the F(ab')2 fragment. The anti-LCS immunoglobulins were observed in patients with non-lymphatic leukaemias but not in the four cases of acute lymphocytic leukaemia studied. Forty percent of the patients with anti-LCS immunoglobulins had high levels of circulating immune complexes, detectable by a competitive test with bovine conglutinin and an enzymatically-active antigen-antibody probe. After cytostatic chemotherapy, the level of circulating immune complexes decreased in all the patients, while the anti-LCS immunoglobulins remained constantly detectable and appeared also in those who were negative at the day of the diagnosis.