[Functional analysis of immune complex-rich serum fractions in autoimmune diseases by in vitro C3 activation of fresh blood].

A method, measuring the activity of circulating immune complexes, based on C3 conversion of fresh human plasma by means of 3 per cent PEG precipitable immune complex-rich sera fractions is reported. Sera of patients suffering from autoimmune diseases of the connective tissue as well as of healthy controls were investigated. In case of standardised protein concentration of immune complexes, significantly low C3 conversion frequency of the isolated fractions has been observed in the control group as compared to the examined patients (rheumatoid arthritis with and without extraarticular manifestations, or juvenile chronic arthritis, or systemic lupus erythematosus). PEG fractions of RA with extraarticular manifestations induced the significantly highest C3 splitting. It is assumed that immune complexes will show a distinct interaction with the complement system also in vivo, and are therefore directly implicated in the systemic course of the disease process.