Activation of the alternative pathway of human complement by haemoglobin

Haemoglobin solutions (concentration greater than 1.5 mg/ml), prepared from lysates of erythrocytes from a normal subject and from a patient with sickle cell anaemia, caused factor B and C3 cleavage and loss of haemolytic activity of factor B wehn incubated with fresh autologous serum. Under the same experimental conditions, preparations of erythrocyte stroma or of buffycoat lysates did not produce factor B and C3 cleavage. This reaction required Mg++ but not C1q or C4, indicating that the alternative complement pathway was activated.