Complement-independent lysis of human red blood cells by cold hemagglutinins.

Hemolysis mediated by human antibodies is generally ascribed to the attack of red blood cells (RBC) by complement. We here extend earlier in vitro observations which indicate that potent cold agglutinins can directly cause lysis of RBC without the participation of complement. We have noted that EDTA plasma taken from patients with cold agglutinin disease is frequently reddish if the plasma is not immediately separated from the cells at 37 degrees C. Moreover, eluates prepared in such cases from plasma or heat-inactivated serum (30 min at 56 degrees C) by absorption (at 4-20 degrees C) and elution (at 37 degrees C) are usually contaminated with hemoglobin, and a large number of RBC used for absorption is lost during the procedure. To characterize this phenomenon further, we examined the effect of different hemagglutinating antibodies in vitro on normal RBC in the absence of complement. Hemolysis (5-17%) of RBC only occurred after treating the cells with potent antibodies at low temperatures (0-20 degrees C). This hemolysis increased 2- to 3-fold when the RBC were treated with an enzyme and decreased with rising temperature. Unlike cells hemolyzed by complement activation, no C5b-9 complexes could be detected on RBC damaged by this mechanism.