The Requirement for the Association of two Adjacent Rabbit γG-Antibody Molecules in the Fixation of Complement by Immune Complexes

Abstract

Summary: An amidinated and benzylated rabbit γG-antibody preparation has been used to study the mechanism of complement fixation. This doubly conjugated antibody retained only 8% of the complement-fixing ability of untreated antibody, but had not lost the ability to combine and precipitate with antigen. It partially suppressed the ability of untreated, complement-fixing rabbit γG-antibody to fix complement, when the two were reacted together with antigen. This effect could be explained if two or more active (untreated) antibody molecules were required to be in close juxtaposition for complement fixation to occur. Under these circumstances, the presence of inactive (treated) molecules would result in a failure of some of the active ones to associate, since there is random co-precipitation of the two types of antibody in the immune lattice. A quantitative study of this suppressive effect led to the conclusion that there is a requirement for two adjacent active γG-antibody molecules acting together in the fixation of complement.