Deviated lysis: lysis of unsensitized cells by complement. V. Generation of the activity of low pH or low ionic strength.

In serum exposed to acid pH (6.4), a serum activity was generated which lyzed unsensitized erythrocytes in the presence of EDTA. It was similar to the d.l. activity found following serum activation by inulin (2). In contrast to the d.l. generation by the classical or by the alternative pathway of C activation, the generation of d.l. by acid pH did not require C4 plus C2 or C3 plus factor B resp. It was, thus, not dependent on any hitherto known pathway of C activation. A similar activity appeared when NHS was centrifuged in a sucrose gradient at low ionic strength. Physicochemical alterations of the component proteins which influence their affinity for each other are seen as the basis for the activation of the attack phase of C.