IFNG and infection: In patients with chronic hepatitis B virus (HBV) infections, the frequency of circulating CD4− NKT cells is lower than that in asymptomatic carriers or healthy controls, but infection did not impair the ability of peripheral NKT cells to produce IFN-γ or IL-4 in response to activation with either α-GalCer or the mitogen phorbol 12-myristate 13-acetate (PMA) (221).