Immunological Study of Anti-M2 in Antimitochondrial Antibody-Negative Primary Biliary Cirrhosis

We investigated the specificity of various autoantibodies in antimitochondrial antibody (AMA)-negative patients with primary biliary cirrhosis (PBC). We examined sera from 144 patients with PBC, 17 of whom were AMA negative by indirect immunofluorescence. The AMA-negative group showed a significantly higher positivity for smooth muscle antibody, but not for antinuclear antibody, as compared with the AMA-positive group. IgG class anti-PDH by enzyme-linked immunosorbent assay (ELIS A) were detected in 13 % of the AM A-negative group. However, all PBC patients showed positive IgG, IgA, and/or IgM class anti-M2 to the four M2 proteins by immunoblotting. These results suggest that the detection of IgG and IgM class anti-PDH and that of antibodies to the four M2 proteins increases the positivity of this ELISA method, and that detection of IgG, IgA, and IgM class anti-M2 to the four M2 proteins by immunoblotting is useful in diagnosing AMA-negative patients with PBC. (Internal Medicine 34: 496-501, 1995)