B-cell activating factor and IL-21 levels predict treatment response in autoimmune hepatitis

Abstract

Background & aims: Increased serum IgG and autoantibodies suggest involvement of B cells in autoimmune hepatitis (AIH). The aim of this study was to assess levels of B cell activating factor of the tumour necrosis family (BAFF), IL-21, and circulating B cell populations in AIH and correlate these to treatment response.

Methods: BAFF and IL-21 levels were determined in 66 patients with AIH before treatment and 10 healthy controls. Flow cytometry was performed on circulating B cells of 10 patients with AIH and 12 healthy controls.

Results: Based on BAFF and IL-21 levels, untreated patients with AIH were divided into 3 groups: 27 (41%) patients with normal BAFF and IL-21 (normal BAFF), 27 (41%) patients with elevated BAFF but normal IL-21 (high BAFF), and 12 (18%) patients with elevated IL-21 (high IL-21). The high BAFF group presented with higher bilirubin compared with the normal BAFF and high IL-21 groups (159 vs. 26 vs. 89 μmol/L; p = 0.001; Mann-Whitney U test). After 12 months of treatment, 54% of the high BAFF group reached remission compared with 34% of the normal BAFF group and 0% of the high IL-21 group (p = 0.006, Chi-square test). During follow-up, 3 patients (25%) with high IL-21 developed primary sclerosing cholangitis (PSC) variant syndrome. Autoimmune-associated B cells were increased in patients with AIH compared with healthy controls (4.4 vs. 1.4%; p = 0.003, Mann-Whitney U test). BAFF levels were correlated positively with naïve B cells (p = 0.01) and negatively with class-switched B cells (p = 0.003) and nonclass-switched B cells (p = 0.005, Spearman correlation).

Discussion: Using BAFF and IL-21, we identified different immunological phenotypes of AIH with a different presentation, treatment response, and outcome. Patients with high IL-21 had the poorest treatment response and a risk of developing PSC variant syndrome. BAFF level was related to shifts in circulating B-cell populations.

Lay summary: In patients with untreated autoimmune hepatitis (AIH), circulating B-cell activating factor of the tumour necrosis family (BAFF), IL-21, and B-cell populations were determined. Three subgroups were identified: with (1) normal BAFF and IL-21, (2) elevated BAFF and normal IL-21, and (3) elevated IL-21. Remission after 1-year treatment occurred in 54, 34, and 0% in Groups 1, 2, and 3, respectively. Group 2 had higher bilirubin, indicating more liver dysfunction. In 25% of patients with high IL-21, AIH-PSC variant syndrome developed, but none in the other groups. Autoimmune-associated B cells were elevated and BAFF levels correlated with certain B cells.

Keywords: AIH, autoimmune hepatitis; ALT, alanine aminotransferase; AP, alkaline phosphatase; AST, aspartate aminotransferase; Autoimmune hepatitis; B-cell immunity; BAFF; BAFF, B-cell activating factor of the tumour necrosis family; Biochemical remission; GGT, gamma-glutamyltransferase; IL-21; LKM-1, liver–kidney–microsomal type 1; MRCP, magnetic resonance cholangiopancreaticography; PBC, primary biliary cholangitis; PBMC, peripheral blood mononuclear cell; PSC, primary sclerosing cholangitis; UDCA, ursodeoxycholic acid; ULN, upper limit of normal.

Graphical abstract

Fig. 1

Levels of BAFF and IL-21 in patients with AIH and healthy controls. (A) Compared with healthy controls, BAFF levels were higher before treatment (p = 0.003, Mann–Whitney U test), and compared with pre-treatment levels, they decreased after treatment (p <0.001, Wilcoxon signed-rank test). (B) IL-21 was elevated only in a subpopulation of patients, and with treatment, these levels remained unchanged compared with pre-treatment values (p = 0.480, Wilcoxon signed-rank test). AIH, autoimmune hepatitis; BAFF, B-cell activating factor of the tumour necrosis family.

Fig. 2

Treatment response in BAFF- and IL-21-based subgroups (Kaplan–Meier survival analysis). Time to first biochemical remission during follow-up was significantly longer in patients with high IL-21 than in patients with high BAFF (p = 0.001) and in patients with normal BAFF (p = 0.045). Patients with high BAFF tended to reach remission faster than patients with normal BAFF (p = 0.052). A value of p <0.050 was the level of significance (log-rank test). BAFF, B-cell activating factor of the tumour necrosis family.

Fig. 3

Prevalence of different B-cell populations in patients with AIH and healthy controls. All B-cell populations are expressed as percentage of B cells except for the total of B cells, which is expressed as percentage of lymphocytes. Median percentages are indicated by lines. The number on top of each figure indicates the p value, with p <0.050 as the level of significance (Mann–Whitney U test). AIH, autoimmune hepatitis.

Fig. 4

Correlation between BAFF level and B-cell populations. (A) Naïve B cells (Spearman correlation r = 0.78; p = 0.01), (B) autoimmunity-associated B cells (Spearman correlation r = -0.26; p = 0.470), (C) no-nclass-switched B cells (Spearman correlation r = -0.83; p = 0.005), and (D) class-switched B cells (Spearman correlation r = -0.85; p = 0.003). A p value <0.050 was considered significant. BAFF, B-cell activating factor of the tumour necrosis family.