Erythrocytes of patients with paroxysmal nocturnal haemoglobinuria acquire resistance to complement attack by purified 20-kD homologous restriction factor.

A 20-kD homologous restriction factor (HRF20) which is a membrane inhibitor of the terminal stage of human complement action can be detected by the monoclonal antibody 1F5, and is deficient on abnormal erythrocytes as well as leucocytes from patients with paroxysmal nocturnal haemoglobinuria (PNH). The erythrocytes of PNH patients significantly improved their resistance to homologous complement after adsorption of purified HRF20.