BACKGROUND: Interleukin-18 (IL-18), a pro-inflammatory cytokine that induces interferon-γ (IFN-γ) production in T cells and natural killer cells, plays a critical role in the T-lymphocyte helper type 1 (Th1) response. This study was designed to explore the effect of IL-18 on peripheral blood mononuclear cells (PBMCs) derived from chronic hepatitis B (CHB) and on hepatitis B virus (HBV) DNA released by HepG2.2.15 cell lines, which were transfected with hepatitis B virus gene in vitro.
METHODS: PBMCs isolated from 25 healthy people and 25 patients with CHB were stimulated with HBcAg and IL-18 of various concentrations for 72 hours. The levels of IFN-γ in the supernatants of cultured PBMCs were determined by ELISA. After the stimulation of IL-18 of various concentrations, PBMCs derived from one patient were co-cultured for 96 hours with HepG2.2.15 cells which had been cultured for 24 hours, and then the supernatants were collected by centrifugation and used for HBV DNA quantitative assay.
RESULTS: When PBMCs were stimulated by HBcAg and IL-18 at various concentrations, the levels of IFN-γ in the supernatants of CHB groups were much higher than those in normal control groups, at 0.2 ng/ml: t=11.70, P<0.01; at 1.0 ng/ml: t=16.19, P<0.01; and at 5.0 ng/ml: t=20.12, P<0.01. In the CHB groups, the levels of IFN-γ in the supernatants of PBMCs stimulated by HBcAg alone were lower than both those stimulated by HBcAg and IL-18 at various concentrations and those stimulated by HBcAg and IL-18 (5.0 ng/ml) together with IL-12 (mild: t=2.20, P<0.05; moderate: t=2.97, P<0.05; severe: t=0.66, P>0.05). The content of HBV DNA in the supernatant of co-cultivation of HepG2.2.15 cells and PBMCs without stimulated materials was higher than that stimulated by HBcAg and IL-18 at various concentrations of HBcAg and IL-18 together with IL-12/IFN-α 1b.
CONCLUSION:  IL-18 can induce IFN-γsecretion and probably play a key role in the modulation of both innate and adaptive immunity. It has implications in improving immunoregulatory effect and increasing the ability of immune cells to kill cells infected by virus.