Binding of complement component C5 to model immune complexes and the use of anti-C5 antibodies for determination of C5-containing circulating immune complexes.

When normal human or mouse serum is added to micro ELISA plates coated with monomeric or aggregated IgG, complement component C5 binds to IgG. C5 binding was demonstrated with a specific chicken anti-C5 antibody. Hydrazine treatment of the serum or addition of EDTA to the serum abolished the binding of C5. C5-deficient mouse serum was negative for C5 binding, whereas the same serum supplemented with human C5 restored the binding of C5. Chicken anti-C5-coated plates were used for determination of C5-containing circulating immune complexes (CIC). Increased concentrations of CIC were found in sera from patients with rheumatoid arthritis and Bell's palsy.