Suppression of the anti-erythrocyte immune response in mice by the C5b--9 complex of complement

The C5b--9 complex of complement associated with sheep erythrocyte membranes suppresses the immune response of mice to sheep erythrocytes as measured with the Jerne plaque technique. This type of immune suppression is independent of early complement components and antibody, and is mediated by both human and guinea-pig complement components. The degree of immune suppression correlates with the number of C5b--9 complexes per cell used for immunization: 21,000 C5b--9 complexes per erythrocyte lead to a 97% inhibition of the immune response in comparison to untreated erythrocytes. Inhibition requires the full assembly of the C5b--9 complex including C8 and C9. Virtually no inhibition was observed by the C5b--7 complex. C5b--9 and IgG-mediated immune suppression do not function additively. From dose-response experiments it is concluded that separate and mutually independent sites mediate suppression by C5b--9 and IgG, respectively.