PROTEASE-MODIFIED ERYTHROCYTES - CD55 AND CD59 DEFICIENT PNH-LIKE CELLS

The increased susceptibility to homologous complement in paroxysmal no cturnal haemoglobinuria (PNH) is known to be associated with the defic iency of the membrane complement inhibitors CD59 and CD55. Proteases h ave been used in this study to modify normal human RBC to complement s ensitive PNH-like cells. To investigate the protective role of CD59 an d CD55, the relationship between the content of CD59 and CD55 and the complement susceptibility of the PNH-like cells has been determined. T he differential resistance of the enzyme-treated RBC to complement-med iated injury was measured by acidified serum lysis. Pronase-treated er ythrocytes lacked both CD59 and CD55 and were very susceptible to comp lement-mediated lysis. Papain treatment of RBC reduced the CD55 conten t but did not affect CD59 and induced slight susceptibility to complem ent-mediated lysis. Trypsin treatment of RBC destroyed 80% of CD59, ha d little effect on CD55 (unless incubation was extended) and slightly increased susceptibility to lysis. Thus, partial CD55 and CD59 activit y was sufficient to protect cells from complement-mediated lysis. In t he reactive lysis assay, anti-CD55 and anti-CD59 induced haemolysis, a nti-CD59 having the more pronounced effect. Lysis was enhanced when RB C were treated by both antibodies simultaneously.