Evidence for the influence of the initial complement components on the assembly and activity of the membrane attack...

The failure of functionally purified C5gp to reconstitute the hemolytic complement (C) activity of C5-deficient human serum was studied. The lack of hemolytic activity of C5gp in this system could not be correlated with the failure of EAC1-3hu to bind and activate C5gp, but was related to the failure of EAC1-3hu5gp6hu to efficiently bind C7hu in a form that would lead to lysis when HuC8 and HuC9 were added. This failure was not observed with EAC1-3gp5gp6hu or EAC1-3hu5hu6hu, which could be lysed with any combination of human or guinea pig C7 through C9. The implications of these findings on the control of the lytic C attack mechanism by the initial components in the C cascade are discussed.