KLRK1 and chronic hepatitis B virus infection: In results, peripheral NKG2D+ and IFN-γ+ NK cells frequencies, intrahepatic NKG2D and IFN-γ mRNA and protein levels, and serum IFN-γ, TNF-α, perforin and granzyme B levels were all highest in HBV-related acute-on-chronic liver failure group, followed by chronic hepatitis B and chronic HBV carrier groups.