Circulating immune complexes and complement activation in primary biliary cirrhosis

We evaluated 20 patients with primary biliary cirrhosis and seven controls with extrahepatic biliary obstruction for presence of circulating immune complexes, having found serologic evidence of alternate complement-pathway activation in eight of the 20. Immune complexes were isolated by cryoprecipitation from serum and measured directly by the sensitive Raji-cell radioimmunoassay. Cryoproteins, found in high concentrations in 90 per cent of the patients with cirrhosis but undetectable in the controls, were composed of IgM (60 per cent), IgG-IgM (25 per cent) and IgA-IgM (5 per cent) and were capable of activating the complement system in vitro. Immune complexes detected by the Raji assay were found in 95 per cent of the patients with cirrhosis and circulated in exceedingly high concentrations (474 microgram per milliliter; range, 16.2 to 2192) but were absent in the controls. Furthermore, the alternate complement pathway was activated in eight cirrhotic patients. These complement-fixing immune complexes differ from immune complexes isolated from other types of liver diseases and may be important in the pathogenesis of primary biliary cirrhosis.