Complement sensitivity of erythrocytes in a patient with inherited complete deficiency of CD59 or with the Inab phenotype

We investigated the complement sensitivity of erythrocytes from three patie nts, one with inherited complete deficiency of CD59, one with the Inab phen otype, and one with paroxysmal nocturnal haemoglobinuria (PNH). The complem ent lysis sensitivity units on the erythrocytes were 11.7, 4.6, and 47.6 fo r inherited CD59 deficiency, Inab phenotype, and PNH, respectively. Two-col our flow cytometric analysis showed that the erythrocytes from the three pa tients consisted of a single population negative for CD59, negative for dec ay accelerating factor (DAF), and negative for both proteins, respectively. In addition, only the Inab phenotype patient had no haemolysis in vivo. Th ese facts suggest that CD59 deficiency plays a more important role than DAF deficiency in complement-mediated haemolysis in vitro and in vivo, and tha t deficiency of both proteins, but not CD59 or DAF alone, causes complement sensitivity corresponding to that of PNH III erythrocytes in vitro.