Implication of membrane factors other than DAF and CD59 in complement-mediated lysis of paroxysmal nocturnal hemoglobinuria erythrocytes.

Erythrocytes from two patients (F.K. and A.M.) with paroxysmal nocturnal hemoglobinuria, which were almost completely deficient in decay-accelerating factor and CD59, were found to differ in their susceptibility to homologous complement. Whereas 50-70% of F.K. erythrocytes were lysed, almost 100% of the erythrocytes from A.M. were lysed. These observations were seen under both acidified and nonacidified conditions, and regardless of whether or not the normal human serum was adsorbed with normal erythrocytes to remove natural antibodies. Erythrocytes from two other patients, J.S. and Y.K., about 85% of which did not express CD59, showed lytic profiles similar to those of patient F.K. The differences between patients were not related to levels of natural antibody or other membrane regulatory proteins such as complement receptor type I or membrane cofactor protein. Erythrocytes from F.K. and A.M. differed in their reconstitution with decay accelerating factor and CD59. While erythrocytes from F.K. were reconstituted with CD59 in a unimodal pattern, erythrocytes from A.M. showed a bimodal pattern of reconstitution assessed by flow cytometry. After reconstitution with CD59, erythrocytes from F.K. and A.M. differed in their protection against homologous complement. It is concluded that erythrocyte membrane constituents other than the known inhibitors differ in these patients.