Significance of natural killer cell G2D expression and activation in patients with different immune status of chronic hepatitis B virus infection

Abstract

Objective To investigate the differences of expression and activation of natural killer (NK) cell G2D (NKG2D) in patients with different immune status of chronic hepatitis B virus (HBV) infection, and to explore the significance of NKG2D-mediated immune injury in HBV infection. Methods Fifteen chronic HBV carriers (immune tolerance), 15 chronic hepatitis B (CHB, immune activation) patients, 15 HBV-related acute/subacute-on-chronic liver failure (HBV-ACLF, immune over-activation) patients were enro1led in this study from January 2010 to December 2011 in the Third Hospital of Hebei Medical University. The frequencies of NK cells and NKG2D+ NK cells in peripheral blood mononuclear cells (PBMC) were detected by flow cytometry. The NKG2D mRNA expressions were measured by real-time fluorescent quantitative polymerase chain reaction. Localization and hemi-quantitative analysis of NKG2D+ cells in liver tissue were performed by immunohistochemistry staining. Concentrations of serum interferon(IFN)-γ, tumor necrosis factor(TNF)-α, perforin and granzyme B were quantified by enzyme 1inked immunosorbent assay (ELISA). Normally distributed continuous variables were analyzed using one-way analysis of variance (ANOVA), followed by Student-Newman-Keuls q test for evaluating variances between each two groups. For non-normally distributed data or heterogeneity of variance, differences between groups were analyzed using nonparametric Kruskal-Wallis H test, followed by Nemenyi test for pairwise comparisons. Pearson chi-square test was used to analyze categorical variables. Results The percentages of NK cells in PBMC were (13.58±3.24)% in healthy controls, (5.42±2.18)% in chronic HBV carriers, (7.92±2.85)% in HBV-ACLF group and (8.43±2.92)% in CHB group.The percentage of NK cells in PBMCs was lower in each chronic HBV-infected group compared with healthy controls (F=22.04, P<0.05). The frequency of NKG2D+ NK cells in HBV-ACLF group (18.92±5.85)% was the highest, followed by CHB group (12.85±3.39)%, healthy controls (8.45±2.86)%, and chronic HBV carriers (3.36±1.05%), with the statistically significant differences between each two groups (H=46.09, P<0.01). Intrahepatic NKG2D mRNA expression and NKG2D+ cells density were highest in HBV-ACLF group (6.58±1.86 and 30.69±6.67, respectively), followed by CHB group (3.25±0.95 and 17.36±4.13, respectively) and chronic HBV carriers (0.69±0.20 and 3.16±1.24, respectively), with the statistically significant differences between each two groups (H=52.10 and 52.73 respectively, both P<0.01). The similar patterns were observed in serum IFN-γ, TNF-α, perforin and granzyme B concentrations. Conclusions NKG2D expresses variously in patients with different immune status of chronic HBV infection. Activation of NKG2D may take part in the immune pathogenesis of chronic HBV infection. Key words: Killer cells, natural; NKG2D; Hepatitis B virus; Hepatitis B, chronic; Acute-on-chronic liver failure