Quantitation of circulating immune complexes in serum by Raji cells using an enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) for the quantitation of immune complexes in sera has been developed using Raji cells. In this assay the Raji cell-adherent complexes are detected by an alkaline phosphatase-conjugated rabbit anti-human IgG and the results are obtained by spectrophotometric measurements of the concentration of yellow colour produced after the enzyme's substrate, p-nitrophenyl phosphate, is added. This assay is as sensitive and reproducible as the Raji cell radioimmune assay using 125I, as it can detect as little as 16 micrograms of immune complex equivalent to heat-aggregated IgG/ml in serum samples. This method is inexpensive, convenient and most importantly, avoids the biohazards of using an isotope.