Role of intestinal barrier in the pathogenesis of autoimmune hepatitis

Objective To observe and analyze the role of intestinal barrier in the pathognesis of autoimmune hepatitis (AIH), to explain the pathogenesis of AIH and to explore the intestinal based new treatment strategies. Methods A total of 14 AIH patients from January to December 2017 at Tianjin Medical University General Hospital (six patients without liver cirrhosis, and eight patients with liver cirrhosis) and 10 healthy controls were enrolled. The serum levels of D-lactic acid (D-Lac) and diamine oxidase (DAO) were detected by enzyme-linked immunosorbent assay. Real time fluorescence quantitative polymerase chain reaction was used to detect the relative expression levels of connexin (zonula occluden-1 (ZO-1), occludin), cytokines (interleukin(IL)-2, interferon(IFN)-γ, IL-4, IL-10) and Toll-like receptor 4 (TLR4) in terminal ileal tissues of each group. The relative expression of secretory immunoglobulin A (sIgA) in the terminal ileum was determined by Western blotting. Thirty BALB/c mice were selected and divided into blank control group, dextran sulfate sodium (DSS) group, concanavalin A (ConA) group, DSS+ ConA group, and DSS+ bacterium+ ConA group, with six mice in each group. The relative expression levels of ZO-1, occludin in mouse colonic tissues, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, and inflammatory activity degree of liver tissues (Knodell score) of each group were measured. T-test and one-way analysis of variance were performed for statistical analysis. Results The serum D-Lac and DAO levels of AIH with liver cirrhosis group and AIH without liver cirrhosis group were both higher than those of healthy control group ((1 768.2±147.1) μg/L, (436.2±197.0) μg/L vs. (100.2±10.9) μg/L, and (11.5±2.5) U/L, (5.4±0.9) U/mL vs. (3.5±0.9) U/mL), and the levels of D-Lac and DAO of AIH with liver cirrhosis group were the highest; and the differences were statistically significant (t=5.512, 36.010, 4.088 and 9.443, F=396.958 and 46.640, all P<0.01). The relative expression levels of ZO-1 and occludin in the terminal ileal mucosa of AIH with liver cirrhosis group were lower than those of healthy control group (0.20±0.14 vs. 1.67±0.51, 0.12±0.09 vs. 0.90±0.21), and the relative expression of ZO-1 in AIH without liver cirrhosis group was lower than that in healthy control group (0.99±0.37 vs. 1.67±0.51); and the differences were statistically significant (t=8.641, 7.407 and 2.295, all P<0.05). The relative expression levels of IL-2 and IFN-γ in terminal ileal tissues of AIH with liver cirrhosis group were higher than those of healthy control group (1.11±0.43 vs. 0.24 ±0.16, and 3.50 ± 1.90 vs. 0.32±0.30), however the relative expression of sIgA in terminal ileal tissues was lower than that of healthy control group (0.506±0.024 vs. 1.081±0.102); and the differences were statistically significant (t=4.679, 3.981 and 5.493, all P<0.05). While the relative expression levels of IL-10 in AIH with liver cirrhosis group and AIH without liver cirrhosis group were lower than that in healthy control group (0.30±0.20, 0.42±0.24 vs. 0.84± 0.23), and the relative expression levels of TLR4 in ileum mucosa of the both groups were higher than that of healthy control group (8.74 ±5.13, 6.74 ±3.65 vs. 0.89 ± 0.70); and the differences were statistically significant (t=3.095, 4.816, 3.856 and 3.685, all P<0.05). The relative expression levels of ZO-1 and occludin of DSS+ ConA group were lower than those of ConA group (0.14±0.08 vs. 0.98±0.13, and 0.09±0.02 vs. 0.98±0.16), however serum ALT, AST levels and the Knodell score were all higher than those of ConA group ((5 496.67±618.83) U/L vs. (3 325.00±1 030.06) U/L, (8 825.00±1 165.35) U/L vs. (5 433.33±1 691.14) U/L, and 18.00±2.00 vs. 9.33±3.01); and the differences were statistically significant (t=13.480, 13.520, 4.227, 4.045 and -2.892, all P<0.05). The relative expression levels of ZO-1 and occludin in DSS+ bacterium+ ConA group were higher than those in DSS+ ConA group (0.46±0.08 vs. 0.14±0.08, and 0.53±0.15 vs. 0.09±0.02), while serum ALT and AST levels were lower than those of DSS+ ConA group ((4 343.33±252.16) U/L vs. (5 496.67±618.83) U/L, and (6 123.33±1 086.60) U/L vs. (8 825.00±1 165.35) U/L); and the differences were statistically significant (t=6.928, 7.122, 4.228 and 4.153, all P<0.01). Conclusions AIH patients have increased intestinal permeability and impaired intestinal barrier which is more serious in patients with liver cirrhosis than in patients without cirrhosis. The intestinal barrier injury can aggravate ConA-induced immune-mediated liver injury. While the protection and repair of intestinal barrier can alleviate immune-mediated liver injury induced by ConA. Key words: Hepatitis, autoimmune; Concanavalin A; Intestinal mucosal barrier; Dextran sulfate sodium; Bifidobacterium