Presence Of Immune Complexes In Sera Research Articles

40] Enzyme immunoassay for the demonstration and quantification of immune complexes

This chapter describes the enzyme immunoassay (EIA) for the demonstration and quantification of immune complexes (IC). The occurrence of circulating IC may be suspected in any patient, undergoing chronic antigenic stimulation. Variation of the level of rheumatoid factor (RF), hypocomplementemia, and presence of cryoglobulins are valuable indirect signs of the presence of IC in sera. The enzyme immunoassay is based upon the inhibition of the binding of a polyclonal RF (PRF) to an IgG-cellulose solid phase by IC in biological fluids. Its principle derives from that of the EIA for RF measurement, and comprises three steps that include: (1) elimination of endogenous RF present in some sera by adsorption onto an aggregated IgG-sepharose sorbent, (2) incubation of the adsorbed samples with a known amount of PRF, and (3) aggregated IgG cellulose. Results obtained with the IC-EIA were correlated with polyethylene glycol precipitation test and Clq binding activity. It is shown that the use of various binding agents leads to the detection of IC, differing by their size, antigen/antibody ratio, and classes of antibody.