Ph Optima in Immune Hemolysis: a Comparison between Guinea Pig and Human Complement.

Certain in vitro hemolytic systems involving human erythrocytes and human serum function more effectively if hemolysis is allowed to proceed in serum that has been slightly acidified, the optimal pH being approximately 6.5. Among such "pHdependent" hemolytic systems are the hemolysis of normal erythrocytes by sera containing high titer cold agglutinins (1); the hemolysis by normal human serum of human erythrocytes whose membranes have been altered by a variety of proteolytic enzymes, chemicals, and viruses (2); the hemolysis of normal human red cells induced by the addition of poly I 1 to normal serum (3); and the hemolysis of red cells from patients afflicted with PNH (4). The diagnosis of PNH usually rests upon what has come to be known as the "acid hemolysis" test (4, 5). The C' system clearly plays a role in all these systems, since removal of any one of the four components of C' from serum renders it incapable of participating in these reactions (la, 2, 3, 6). On the other hand, it has been suggested that some other mechanism may be involved in red cell ly-