Expression and clinical significance of the NK cell-activating receptor NKG2D and its ligand in liver tissue of patients with primary biliary cholangitis

Objective To investigate the association of the expression of the NK cell-activating receptor NKG2 D,its ligand major histocompatibility complex class I chain-related gene A( MICA),and related cytokines [interferon-γ( IFN-γ),interleukin-10( IL-10),and interleukin-15( IL-15) ] with intrahepatic inflammation in primary biliary cholangitis( PBC). Methods Liver biopsy specimens were collected from 30 patients with PBC( PBC group),15 patients with chronic hepatitis B( CHB group),and 10 patients with nonalcoholic fatty liver disease( NAFLD group),who were hospitalized in The Second Affiliated Hospital of Kunming Medical University from August 2014 to June 2015. The degree of liver inflammation( G) and fibrosis degree( S) of the liver specimens were determined,and immunohistochemistry was used to measure the expression of NKG2 D,MICA,IFN-γ,IL-10,and IL-15 in liver tissue( the scores were determined based on the number of cells stained and the degree of staining to evaluate the expression of each marker). A one-way analysis of variance was used for comparison of continuous data between multiple groups,and the t-test was used for comparison between two groups; a Spearman correlation analysis was used to investigate correlation. Results In the PBC group,the expression of NKG2 D increased with the degree of inflammation,and the patients with G3-4 inflammation had significantly higher expression than those with G1-2 inflammation( G1 vs G2 vs G3 vs G4: 1. 4 ± 0. 05 vs 1. 56 ± 0. 05 vs 1. 86 ± 0. 11 vs 2. 60 ± 0. 17,F = 150. 8,P < 0. 05); the expression of NKG2 D decreased with fibrosis degree( S3 vs S4: 2. 30 ± 0. 17 vs 1. 56 ± 0. 05,t =-1. 52,P < 0. 05). In the PBC group,there was no significant difference in MICA between G3 and G4( 0. 11 ± 0. 01 vs 0. 20 ± 0. 03,t =-2. 20,P > 0. 05) and between S3 and S4( 0. 12 ±0. 02 vs 0. 18 ± 0. 03,t =-2. 64,P > 0. 05). In the PBC group,there was a significant difference in the expression of IL-15 between the patients with different degrees of inflammation( G1 vs G2 vs G3 vs G4: 0. 70 ± 0. 10 vs 1. 50 ± 0. 10 vs 1. 93 ± 0. 11 vs 2. 60 ± 0. 17,F =251. 3,P < 0. 05),while there was no significant difference between the patients with different fibrosis degrees( S3 vs S4: 2. 00 ± 0. 05 vs2. 40 ± 0. 30,t =-1. 62,P > 0. 05). In the CHB group,there was a significant difference in the expression of IL-15 between the patients with different degrees of inflammation( G1 vs G2 vs G3: 0. 73 ± 0. 15 vs 1. 96 ± 0. 15 vs 2. 50 ± 0. 17,F = 150,P < 0. 05) and between the patients with different fibrosis degrees( S1 vs S2 vs S3: 0. 70 ± 0. 10 vs 21. 96 ± 0. 15 vs 2. 50 ± 0. 17,F = 158. 7,P < 0. 05). In the PBC group,the expression of IL-10 was only observed in the patients with G1 inflammation( 0. 16 ± 0. 01),and in the CHB group,the expression of IL-10 was observed in the patients with G1 and G2 inflammation,with no significant difference( G1 vs G2: 0. 19 ± 0. 01 vs0. 13 ± 0. 01,t =-1. 522,P > 0. 05). In the patients with PBC,the expression of IL-15 in liver tissue was positively correlated with the levels of alkaline phosphatase( ALP) and gamma-glutamyl transpeptidase( GGT)( r = 0. 241 and 0. 407,P = 0. 014 and 0. 045).Conclusion The NK cell-activating receptor NKG2 D affects the degree of intrahepatic inflammation in PBC,and the NKG2 D ligand MICA is expressed in the advanced stage of PBC and can downregulate NKG2 D. The expression of IL-15 increases with the degree of inflammation in PBC and is positively correlated with the levels of ALP and GGT,suggesting that the activation of NK cells and abnormal secretion of cytokines are involved in the development and progression of PBC and IL-15 may be used as an auxiliary index for the diagnosis of PBC.