Evidence of increased intestinal synthesis and extracellular deposition of IgM in primary biliary cirrhosis. An immunofluorescence study of liver and small-intestinal biopsy specimens.

Direct immunofluorescence showed intense extracellular granular deposition of IgM and C3 in liver and small-intestinal biopsy specimens from patients with primary biliary cirrhosis. In contrast, IgM deposits were not observed in liver tissue from patients with other liver diseases, whereas small-intestinal IgM deposits were seen also in 2 of 17 patients with various intestinal disorders. The tissue deposition of IgM did not vary with plasma IgM levels, degree of cholestasis, or histological stage of the disease but seemed to reflect an abnormal property of the IgM molecule. The number of IgM-positive mononuclear cells in intestinal mucosa from patients with primary biliary cirrhosis was markedly increased, suggesting increased local synthesis of IgM. Deposition of IgM with complement-activating ability might contribute to the development of tissue damage in primary biliary cirrhosis. In addition, the apparent specificity of these IgM deposits in liver for primary biliary cirrhosis might be of diagnostic value when histological classification is difficult.