Frequency and role of NKp46 and NKG2A in hepatitis B virus infection

Abstract

Background and AimNatural Killer (NK) cells are involved in the control of viral infection. However, the role of NK cells in chronic hepatitis B (CHB) remains unclear. This study investigated the frequencies and roles of NK cells in CHB, with a focus on activating receptor NKp46 and inhibitory receptor NKG2A.Patients/MethodPeripheral blood lymphocytes were obtained from 71 CHB patients and 37 healthy subjects (HS). The expressions of NKp46 and NKG2A were analyzed using flow cytometry. The role of NKp46-ligand was assessed using an in vitro co-culture system. Cytotoxicity and IFN-γ production in NK cells were evaluated using RT-PCR and flow cytometry.ResultsCHB patients were classified into treatment-naïve patients with low HBV DNA titer (CHB-L; n = 28), high HBV DNA titer (CHB-H; n = 24) by the cut-off level of serum HBV DNA 4 log copies/ml, and patients receiving nucleos(t)ide analogue (CHB-NA; n = 19). The expressions of NKp46 and NKG2A were higher in CHB-H than in HS/CHB-L/CHB-NA. HepG2.2.15 had higher NKp46-ligand expression than HepG2. When NK cells from HS were co-cultured with HepG2.2.15, inhibition of the NKp46 and NKp46-ligand interaction by anti-NKp46 antibody significantly reduced cytolysis of HepG2.2.15 and IFN-γ production. However, those reductions were not observed in co-culture with HepG2. Additionally, NK cells that highly expressed NKp46 also highly expressed NKG2A (NKp46highNKG2Ahigh subset). The frequencies of NKp46highNKG2Ahigh subset in CHB-H were higher than those in HS/CHB-L/CHB-NA. Among treatment-naïve CHB patients, the frequencies of NKp46highNKG2Ahigh subset were positively correlated with serum ALT (P<0.01, r = 0.45) and HBV DNA (P<0.01, r = 0.59) levels. The expressions of Fas-L, STAT1, TRAIL and CD107a were higher and IFN-γ expression was lower in the NKp46highNKG2Ahigh subset than in the other subsets.ConclusionThe NKp46 and NKp46-ligand interaction contributes to NK cell activation. A novel NK cell subset, the NKp46highNKG2Ahigh subset, may be associated with liver injury and HBV replication.

Immune function of plasmacytoid dendritic cells, natural killer cells, and their crosstalk in HBV infection

“…This high frequency was also positively correlated with serum ALT and HBV DNA levels. This subset of NK cells showed high cytotoxicity and low production of IFN‐γ and was associated with liver injury, which is in line with the functional dichotomy of NK cells in viral hepatitis …”

“…Studies that evaluated the level of NKG2A, as inhibitory receptor, on NK cells of CHB patients show discrepancies, like other receptors (Table ). Some studies show elevated level of NKG2A, while others show similar or even decreased level of this receptor on NK cells of CHB patients compared with that of healthy subjects . Results of in vitro studies showed that blockade of NKG2A by monoclonal antibodies enhanced cytotoxicity of NK cells isolated from active CHB patients; furthermore, blockade of NKG2A or its ligand Qa‐1 considerably promoted HBV clearance in HBV‐carrier mice .…”

“…Results of in vitro studies showed that blockade of NKG2A by monoclonal antibodies enhanced cytotoxicity of NK cells isolated from active CHB patients; furthermore, blockade of NKG2A or its ligand Qa‐1 considerably promoted HBV clearance in HBV‐carrier mice . Additionally, antiviral therapy in CHB patients leads to downregulation of NKG2A …”

“…This study reported NKp46‐ligand expression in HBV‐producing cell lines. In other words, viral replication often causes upregulation of these ligands and contributes to the activation of NK cells, which makes infected cells highly susceptible to killing by NK cells …”

“…52 There are discrepancies and conflicting results regarding NK cell frequency, phenotype, and function in CHB patients (Table 3). Some studies report that there is no difference in the NK cell numbers (total percentage) and subset distribution between HBV patients and normal individuals [56][57][58] or among different HBV clinical groups, 59 while more studies describe a lower number of NK cells 34,[60][61][62][63] and also NKG2D positive NK cells 61 in CHB patients compared with healthy subjects.…”