Correlation between anti-mitochondrial antibodies and clinical serological and cirrhotic markers of primary biliary cholangitis

Objective To explore the correlation between the level of anti-mitochondrial antibody (AMA) and clinical indicators of first visited primary biliary cholangitis (PBC) patients with positive AMA. Methods From January 2013 to December 2016, the clinical data of 1 323 patients with positive AMA and/or AMA-M2 detected for the first time were collected through the Information System of Peking University People′s Hospital. Among them, 183 were detected by indirect immunofluorescence assay, 431 were measured by immunoblotting, and 709 were determined by enzyme-linked immunosorbent assay (ELISA). Patients were divided into undiagnosed PBC group (non-PBC group, 973 cases) and newly diagnosed PBC group (new-PBC group, 350 cases including 268 cases of non-liver cirrhosis and 82 cases of liver cirrhosis); among 709 cases detected by ELISA, there were 567 cases in the non-PBC group and 142 cases in the new-PBC group (115 cases of non-liver cirrhosis PBC group and 27 cases of liver cirrhosis PBC group). Among 183 cases determined by indirect immunofluorescence assay, there were 118 cases in the non-PBC group and 65 cases in the new-PBC group. Among them 69 cases with low AMA titer (1∶40—1∶80) (53 cases of non-PBC group and 16 cases of new-PBC group), 95 cases with medium titer (1∶160—1∶320) (59 cases of non-PBC group and 36 cases of new-PBC group) and 19 cases with high titer (≥1∶640) (six cases of non-PBC group and 13 cases of new-PBC group). AMA levels among groups were compared, and its correlation with clinical serology and cirrhosis indicators of PBC including immunoglobulin (Ig)G, IgM, platelet, alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyltranspeptadase (GGT), alkaline phosphatase (ALP), serum total protein, serum albumin, total bilirubin (TBil), total cholesterol (TC), and aspartate aminotransferase to platelet ratio index (APRI) and fibrosis (Fib-4) was analysed. Mann-Whitney U test, Kruskal-Wallis test, and linear regression analysis were performed for statistical analysis. Results By ELISA method, the median titer of AMA-M2 of 709 patients was 53 RU/mL, the serum AMA and AMA-M2 levels of new-PBC group were both higher than those of non-PBC group (1∶320 vs. 1∶80, 180 RU/mL vs. 47 RU/mL), and the differences were statistically significant (χ2 = 14.111, Z = -7.531, both P 0.05). AMA-M2 value of patients in PBC with liver cirrhosis group was positively correlated with IgM level (r = 0.38, P = 0.039), but was not correlated with APRI and Fib-4 (all P > 0.05). The median of AMA value of 183 patients who underwent indirect immunofluorescence test was 1∶160. In non-PBC group, the IgM levels of patients with low, medium and high AMA titers gradually increased (the median levels were 1.2, 1.7 and 1.8 g/L, respectively); in new-PBC group, the levels of IgM, GGT and ALP of patients with low, medium and high AMA titers gradually increased (median IgM levels were 1.5, 3.7 and 4.1 g/L, respectively; GGT levels were 144, 182 and 317 U/L, respectively; and ALP levels were 137, 168 and 221 U/L, respectively), and the differences were statistically significant (χ2 =6.260, 7.081, 8.030, 15.226, all P<0.05). In non-PBC group, the median level of serum AMA-M2 of men was lower than that of women (41 RU/L vs. 50 RU/L), and the difference was statistically significant (Z = -2.945, P = 0.003). In new-PBC group, the median level of serum AMA-M2 of men tended to be lower than that of women (113 RU/mL vs. 206 RU/mL), but the difference was not statistically significant (P=0.257). Conclusion Serum AMA level is correlated with many clinical parameters and may be related with the disease severity in patients with PBC. Key words: Anti-mitochondrial antibody; Primary biliary cholangitis; Liver cirrhosis; Clinical significance