摘要AIM: To assess the role of IgM and IgG immunohistochemistry (IHC) in the evaluation of autoimmune liver conditions -autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC).METHODS: Forty one biopsies from untreated patients diagnosed with autoimmune liver disease (AIH, n =20; PBC, n = 13; PSC, n = 8) and fourteen biopsies of patients with chronic hepatitis C were selected. IgM and IgGpositive plasma cells were counted in each sample.RESULTS: A predominance of IgGpositive plasma cells was seen in AIH (90% of cases), PSC (75% of cases),and chronic hepatitis C (100% of cases), while IgMpositive plasma cells predominated in PBC (92.8% of cases). The IgM /IgG ratio (< 1 or ≥ 1) accurately distinguished PBC from AIH in 90.9% of cases (sensitivity = 92.3%, specificity = 90%), and PBC from either AIH or PSC in 87.8% of cases (sensitivity = 92.3%,specificity = 85.7%).CONCLUSION: Plasmacytic infiltrates expressing predominantly IgM are characteristic of PBC, while other forms of liver disease analyzed in this study, including AIH, typically show an IgGpredominant plasma cell infiltrate. Our data indicate that IgM and IgG IHC may be a useful tool when PBC is a diagnostic consideration.