Application of Histopathology, Immunohistochemistry, and Antibody Titers in the Diagnosis and Treatment Response Assessment of Autoimmune Liver Diseases

Objective To investigate the differences in histopathological characteristics, immunohistochemical marker expression, and serum antibody titers among autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), AIH-PBC overlap syndrome (OS)[39], and drug-induced autoimmune-like hepatitis (DI-AILH), providing basis to enhance the accuracy of differential diagnosis and rational prediction of treatment response. Methods A retrospective collection of liver biopsy specimens from 40 patients at the Department of Gastroenterology, Leshan People's Hospital, between January 2022 and August 2025 was conducted, including 11 AIH cases, 11 PBC cases, 10 AIH-PBC OS cases, and 8 DI-AILH cases. A comprehensive approach utilizing HE staining (assessing inflammation grade, fibrosis stage, and characteristic pathological changes), immunohistochemistry (detecting markers such as Mum-1, CD38, CD3, CD68), serum antibody titers (anti-nuclear antibody, ANA), and liver biochemical indices (ALT, ALP, IgG) was employed to quantitatively compare histological and immunohistochemical differences among the four groups. Patients with AIH, PBC, and OS were followed up for 6 months to analyze the correlation between treatment response and antibody titers, biochemical indices, and pathological changes. Results Both the AIH and OS groups exhibited significant interface hepatitis, hepatocyte rosette formation, and emperipolesis. The scores for portal plasma cell + lymphocyte infiltration [AIH: (2.00 ± 1.61), (3.91 ± 0.30); OS: (1.90 ± 1.20), (3.70 ± 0.48)] were significantly higher than those in the PBC group [(1.00 ± 0.63), (2.55 ± 1.13)] and the DI-AILH group [(0.38 ± 0.52), (2.38 ± 1.30)] (all P < 0.05). Inflammation grade (Scheuer grade) [AIH: (3.64 ± 0.50), OS: (3.00 ± 0.67)] and fibrosis stage (Scheuer stage) [AIH: (3.09 ± 0.83), OS: (2.80 ± 0.79)] were also higher in the AIH and OS groups compared to the other two groups (all P < 0.05). Serologically, the proportion of high-titer ANA (≥ 1:640) in the OS group was 80.0% (8/10), significantly higher than in other groups (P < 0.05). IgG levels in the AIH group [2520.00 (2190.00, 3565.00)] were significantly higher than in the other three groups (P < 0.05), while ALT levels in the DI-AILH group (360.12 ± 420.84) were significantly higher than in the other three groups (all P < 0.05). The 6-month follow-up showed no significant difference in the complete biochemical response rate between the AIH and OS groups (P > 0.05). Non-responders in the PBC group had significantly higher ALP and ALT levels [ALP: 917.00 ± NA; ALT: 215.00 ± NA] compared to responders [ALP: 195.50 ± 95.68 U/L; ALT: 64.40 ± 47.68 U/L] (both P < 0.05). Multivariate logistic regression analysis showed that elevated IgG was an independent diagnostic factor for AIH (OR = 1.02, 95% CI: 1.00-1.04, P < 0.05), and high-titer ANA was an independent predictive factor for OS (OR = 3.41, 95% CI: 1.12–10.38, P < 0.05). Immunohistochemical features: OS showed the most prominent CD3 and CD38 expression, reflecting dual "cellular immunity + immune activation" overlay. AIH exhibited active CD68 and Mum-1 expression, suggesting a combined "cellular immunity (macrophages) + humoral immunity" drive. PBC had Mum-1 levels comparable to AIH but lower T-cell and immune activation involvement, leaning towards "humoral immunity + bile duct-specific injury". DI-AILH generally showed lower involvement of all immune markers, reflecting the fundamental difference of its "drug-induced" immune injury mechanism compared to traditional autoimmune liver diseases. Conclusion Combining histopathological features (interface hepatitis, rosette formation), immunohistochemical markers (Mum-1, CD3, CD38, CD68), and serological indices (IgG, ANA titer, ALT) can effectively differentiate AIH, OS, PBC, and DI-AILH, improving diagnostic accuracy. Early identification of OS and selection of targeted immunosuppressive regimens can improve treatment response. Pre-treatment ALP and ALT levels in PBC patients can serve as important reference indicators for second-line treatment decisions.