Possibly specific immune complexes in sera of patients with untreated acute myelogenous leukemia.

Eleven patients with acute myelogenous leukemia (AML) in the acute stage of the disease were studied. Sera of seven patients were assayed for complement-dependent cytotoxicity to autochthonous AML cells and sera of four patients were tested with allogeneic target cells before and after ultrafiltration at low pH. No specific cytotoxic activity could be detected in any untreated sera. Ultrafiltration at low pH led, however, to the appearance of a significant cytotoxic activity in all of seven autochthonous and in three of four allogeneic combinations. Identical treatment of control AB sera did not result in any similar activity. The results show that potentially cytotoxic antibodies to leukemia-associated antigens are present in the acute stage of acute myelogenous leukemia. However, they do not express complement-dependent cytotoxicity in untreated sera. After ultrafiltration at low pH significant complement-dependent cytotoxicity was detectable in most of the sera. One possible explanation is that cytotoxic antibodies to leukemia-associated antigens are present in the form of circulating immune complexes. Splitting of them at low pH and elimination of the antigen component might result in an increased amount of free cytotoxic antibodies.