A quantitative enzyme-linked immunoassay for serum immune complexes.

A sensitive, quantitative, non-complement dependent enzyme-linked immunoassay (ELIA) for human serum immune complexes has been developed utilizing the L1210 murine leukemia cell and peroxidase-conjugated anti-IgG. At end-point O-dianisidine dihydrochloride method was developed which detects as little as 16.45 x 10(-5) purpurogallin units of horse radish peroxidase. The L1210 ELIA requires only five microliters of serum and reproducibly quantitates as little as 55 nanograms of an artificial immune complex standard (heat aggregated IgG). The validity of using aggregated IgG as a standard was demonstrated by the fact that it produced a dose dependent inhibition of binding of a known immune complex (peroxidase-anti-peroxidase) to the L1210 cells whereas monomeric IgG showed no inhibition. Results of the L1210 ELIA are similar to those of the L1210 radioimmune assay (RIA) which we have previously reported. There was no significant difference in mean immune complex levels between the ELIA and the RIA when serums from normal healthy blood donors were tested. A strong correlation (rs equals +0.787) of immune complex levels as determined by the ELIA and the RIA was found in 17 serum samples from patients with disease associated with elevated levels of circulating immune complexes.