A new enzymatic assay for evaluating the clearance of immune complexes from the circulation of mice

Abstract

A new photometric in vivo enzymatic immune complex clearance (EIC) assay was developed in a homologous system using glucose oxidase-anti-glucose oxidase complexes (GAG) as a model of immune complexes. Chromatographically purified GAG was injected into mouse tail veins and at intervals thereafter the enzyme activities of GAG remaining in the circulation were estimated. The GAG were cleared in a size dependent manner and were stable, being eluted as the same discrete peaks on HPLC size-exclusion chromatography both before and after injection into mice. The complement consuming activity of the GAG was weak, and depletion of complement components with cobra-venom factor did not alter clearance of the GAG from the circulation, whereas pretreatment of aggregated mouse gamma globulin suppressed the clearance rate. These results suggested that most of the GAG were not cleared via complement receptors but via FcR. Normal clearance rates were significantly changed by administration of immunomodulators such as carrageenan or LPS. Intravenous administration of GAG at a dose 50 times higher than normal caused no deaths suggesting that the complexes were of low toxicity. The enzymatic method presented should be of value for measuring the function of the mononuclear phagocytic system with respect to immune complex clearance. It provides a rapid and sensitive alternative assay which avoids using radioisotopes.