The Hemolysis of Red Cells from Patients with Paroxysmal Nocturnal Hemoglobinuria by Partially Purified Subcomponents of the Third Complement Component*

Abstract

Partially purified preparations of a subcomponent of the third component of complement (C [image]3a) are capable of attaching directly to red cells of patients with paroxysmal nocturnal hemoglobinuria (PNHE). The intermediate complex thus formed (PNHEC[image]3a), in contradistinction to PNHE, is susceptible to hemolysis by high dilutions of human serum in the absence of Ca++ or Mg++. PNHEC[image]3a will hemolyze in serum lacking properdin, or the first, second, or fourth components of complement, but not in serum depleted of C[image]3 by zymosan. Hemolysis of PNHEC[image]3a can be effected by partially purified late-acting subcomponents of C[image]3, and the behavior of PNHEC[image]3a in all respects resembles that of their counterpart in classical immune lysis, EAC[image]1,4,2,3a. Normal human red cells are also susceptible to hemolysis by partially purified subcomponents of C[image]3, but to a much lesser extent than PNHE. These findings confirm earlier speculation that in ordinary acid hemolysis in whole human serum, early fluid phase events in C[image] activation lead to direct attack of PNHE by C[image]3, without the mediation of cell bound complement components. The difference between normal human red cells and PNHE would appear to be a difference involving the number of accessibility of membrane sites concerned with the attachment of C[image]3a.