Lytic activity of C5-9 complexes for erythrocytes from the species other than sheep: C9 rather than C8-dependent variation in lytic activity

With the reactive lysis system, a form of hemolysis mediated solely by the late-acting complement components (C56, C7, C8, and C9), guinea pig C9 (C9(gp)) was found to be very inefficient in inducing the lysis of guinea pig and mouse erythrocytes bearing human C5-8. By contrast, C9(gp) could efficiently induce the lysis of sheep and goat erythrocytes bearing human C5-8. By contrast, C9(gp) could efficiently induce the lysis of sheep and goat erythrocytes bearing human C5-8. Human C9 was efficient in the lysis of erythrocytes from the species mentioned above. Further study showed: 1) the observed inefficiency in the lysis of guinea pig erythrocytes was not due to incompatibility between human C7 or C8 and C9(gp); 2) C9(gp) could efficiently bind to guinea pig erythrocytes bearing human C5-8 but was inactive in the subsequent lytic process. The present finding emphasizes a role for C9 in complement-mediated membrane damage which may not be a simple effector function of C8 action.