Flow cytometric determination of circulating immune complexes with the indirect granulocyte phagocytosis test

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Abstract
A method for the determination of circulating immune complexes (CIC) was adapted for flow cytometric analysis. Human granulocytes were used to phagocytose IgG‐bearing CIC of serum from systemic lupus erythematosus (SLE) patients. A method for labeling the phagocytosed CIC with FITC‐conjugated anti‐human IgG was developed where the granulocytes remain in suspension during fixation and labeling. The fluorescence per cell, measured with a flow cytometer, is a measure of the total amount of the phagocytosed IgG. The results indicate that a rapid and quantitative method for the detection and measurement of phagocytosed CIC is possible using the flow cytometer.