Diagnostic utility of IgG and IgM immunohistochemistry in autoimmune liver disease.

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 IgG-positive plasma cells were counted in each sample. RESULTS: A predominance of IgG-positive plasma cells was seen in AIH (90% of cases), PSC (75% of cases), and chronic hepatitis C (100% of cases), while IgM-positive 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 IgG-predominant plasma cell infiltrate. Our data indicate that IgM and IgG IHC may be a useful tool when PBC is a diagnostic consideration.