Elevation of interleukin-18 in chronic hepatitis C: implications for hepatitis C virus pathogenesis

Abstract

The outcome of hepatitis C virus (HCV) infection is determined by the interplay between the virus and the host immune response. Interleukin (IL)-18, an interferon-gamma-inducing factor, plays a critical role in the T helper type 1 (Th1) response required for host defence against viruses, and antibodies to IL-18 have been found to prevent liver damage in a murine model. The present study was conducted to investigate the possible role of IL-18 in the pathogenesis and persistence of HCV. IL-18 levels were measured in sera of 50 patients at various stages of HCV infection (resolved, chronic and cirrhosis) and compared with those of normal controls. IL-18 gene expression was studied in peripheral blood mononuclear cells (PBMC) from each group, and in liver biopsy tissue from patients with chronic hepatitis C. The mean levels of IL-18 in sera were markedly elevated in patients with chronic hepatitis and cirrhosis, and were reduced in patients with resolved HCV infection. The serum IL-18 concentrations were related to the Child-Pugh severity of liver disease in cirrhotic patients. There also existed a strong positive correlation of IL-18 levels with histological activity score and necrosis. IL-18 mRNA expression was significantly up-regulated in the PBMC of cirrhotic patients when compared with other groups, while in the liver, higher levels of IL-18 transcripts were expressed in patients with chronic hepatitis C. The results of our study indicate that IL-18 levels reflect the severity and activity of HCV infection, and may contribute to the pathogenesis and progression of liver disease associated with HCV.

Figure 1

Serum interleukin (IL)-18 levels are elevated in patients with chronic hepatitis C and cirrhosis. IL-18 production was measured in the sera of 50 patients at various stages of hepatitis C virus (HCV) infection and 15 controls using a commercial enzyme-linked immunosorbent assay (ELISA) system. The mean levels of IL-18 were 140·9 ± 81·7 pg/ml in the resolved HCV group (G 1), 865·4 ± 283·4 pg/ml in the chronic hepatitis C group (G 2), 1315·5 ± 714·1 pg/ml in the group of cirrhotic patients (G 3) and 297·6 ± 88·6 pg/ml in normal healthy controls (G 4). The increase in serum IL-18 was significant in group 2 (P< 0·005) and group 3 patients (P< 0·005) as compared with the control group 4.

Figure 2

Interleukin (IL)-18 levels in serum correlate with Child–Pugh severity in cirrhosis. The patients with hepatitis C virus (HCV)-related cirrhosis were graded by calculating the Child–Pugh severity index based on their laboratory and clinical findings. The mean levels of IL-18 in patients with Child–Pugh stages A, B and C were 798·7 ± 162·9, 1142·6 ± 109·2 and 2220·7 ± 852·7 pg/ml, respectively. IL-18 levels correlated with the severity of liver dysfunction according to the Child–Pugh classification in patients with cirrhosis (r = 0·777; P< 0·05).

Figure 3

Interleukin (IL)-18 mRNA expression is up-regulated in the peripheral blood mononuclear cells (PBMC) of cirrhotic patients and in the livers of patients with chronic hepatitis C. The gene expression of IL-18 was studied using semiquantitative reverse transcriptase–polymerase chain reaction (RT-PCR) which yielded products of 342 bp for IL-18 (upper panel) and 983 bp for GAPDH (lower panel). The densitometric assessment was performed using scion image analysis software and the results are expressed as the ratio of IL-18:GAPDH mRNA in PBMC of (a) subjects with resolved hepatitis C virus (HCV) infection, (b) chronic hepatitis C patients, (c) patients with HCV-related cirrhosis, and (d) normal healthy controls. IL-18 mRNA expression in the PBMC of cirrhotic patients was significantly up-regulated compared with that in the resolved (P< 0·001), chronic hepatitis (P< 0·01) and control groups (P< 0·001). (e) The patients with chronic hepatitis C (lanes 4–9) expressed significantly higher levels of IL-18 transcripts in the liver (P< 0·025) compared with the controls (lanes 1–3).

Figure 4

Interleukin (IL)-18 levels in sera show a strong positive correlation with hepatic histological activity in patients with chronic hepatitis C. The hepatitis activity index (HAI) score, reflecting severity, was determined in liver biopsies of 20 patients using the modified Knodell system. The mean IL-18 concentration in patients with HAI scores > 7 was higher than that in patients with HAI ≤ 7 (1101·1 ± 235·5 versus 672·5 ± 131·5 pg/ml, respectively), and IL-18 production was strongly associated with HAI (correlation coefficient r = 0·945; P< 0·001).