Expression of cryptantigen Th on paroxysmal nocturnal hemoglobinuria erythrocytes in association with a hemolytic exacerbation.

Paroxysmal nocturnal hemoglobinuria (PNH) erythrocytes lack complement regulatory membrane proteins and are susceptible to complement. Although the critical role of complement in intravascular hemolysis in PNH is accepted, the precise mechanism of complement activation in vivo is unknown. Accordingly, in a PNH patient who was suffering from a hemolytic precipitation soon after a common cold-like upper respiratory infection, we analyzed the erythrocytes with lectins and by flow cytometry to detect membrane alteration that lead to complement activation. The lectin reactivity of erythrocytes showed the expression of cryptantigen Th. The patient serum at the time of the hemolysis induced the expression of Th on erythrocytes from PNH patients and from healthy volunteers in vitro, whereas neither the patient serum after recovery from the hemolysis nor blood type-matched control serum from healthy donor showed this activity. Moreover, autologous serum selectively hemolyzed Th+ PNH erythrocytes, but not Th- PNH erythrocytes, or Th+ control erythrocytes. Hemolysis was not observed either in complement-inactivated serum or in blood type-matched cord blood serum, which lacks natural antibodies to cryptantigens. These findings indicate that the immunoreaction of infection-induced Th with natural antibody on PNH erythrocytes is a trigger of the complement activation, leading to intravascular hemolysis.