Exogenous Interleukin-37 Alleviates Hepatitis with Reduced Dendritic Cells and Induced Regulatory T Cells in Acute Murine Cytomegalovirus Infection

Abstract

Human cytomegalovirus (HCMV) infection is globally distributed, and the liver is one of the major targeting organs. So far, the mechanisms for cell and organ damage have not fully been elucidated and the treatments for the infection are mainly at symptoms. IL-37 has shown a protective role in certain inflammatory diseases. In the present study, potential protective effect of exogenous IL-37 on murine cytomegalovirus- (MCMV-) infected hepatitis was evaluated through analyses of serum transaminases, the liver histopathology and cytokine expression, and functional state of dendritic cells (DCs) and regulatory T cells (Tregs). These analyses showed a significant decrease in serum transaminase levels and a lower Ishak histopathologic score at the early stage of MCMV-infected mice with exogenous IL-37 pretreatment. The frequencies of MHC-Ⅱ, CD40, CD80, and CD86 positive DCs in the liver and spleen were decreased significantly at 7 days postinfection (dpi) in MCMV-infected mice with IL-37 pretreatment when compared with those without the pretreatment, while the total number of DCs in the liver was reduced in IL-37-pretreated mice. The induction of Tregs in the spleen was enhanced at dpi 3 with IL-37 pretreatment in MCMV-infected mice. The mRNA expression levels of cytokines in the liver were decreased significantly (IL-1β, IL-6, IL-10, IL-4) or to some extent (TGF-β and TNF-α). The present study suggested that exogenous IL-37 can alleviate MCMV-infected hepatitis, likely through reduced DCs and induced Tregs with a weaker cytokine storm, demonstrating its potential value in clinical management for HCMV-infected hepatitis.

Figure 1

Protective effect of exogenous IL-37 on MCMV-induced hepatitis in mice (n = 3 − 5 mice in each group): (a) quantitative analysis of serum ALT and AST at dpi 3, 7, and 14 ( ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001); (b) representative images of liver sections rom mice of the four groups at dpi 3, 7, and 14, scale = 50 μm. (c) Quantitative analysis of Ishak score ( ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001) of liver in experimental groups on dpi 3, 7, and 14.

Figure 2

Effects of IL-37 on the accumulation and maturation of DCs in the liver of MCMV-infected mice at the early stage of viral hepatitis (n = 3 − 5 mice in each group): (a) distribution and quantitative analysis of CD11⁺ cells with the area under curve (AUC) at dpi 3, 7, and 14; (b–e) the frequencies of MHC-Ⅱ-, CD40-, CD80-, and CD86-positive DCs at dpi 3, 7, and 14 and quantitative analysis of DC subsets in flow cytometry.  ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001.

Figure 3

Effects of IL-37 on MCMV-induced accumulation and maturation of DCs in the spleen of MCMV-infected mice (n = 3 − 5 mice in each group): (a) distribution and frequency of CD11⁺ cells at dpi 3, 7, and 14; (b–e) frequencies of MHC-Ⅱ-, CD40-, CD80-, and CD86-positive DCs at dpi 3, 7, and 14 and quantitative analysis of DC subsets in flow cytometry.  ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001.

Figure 4

Effects of IL-37 on the induction and activation of Tregs in the spleen of MCMV-infected mice (n = 3 − 5 mice each group). Representative diagrams of flow cytometry and quantitative analysis of CD4+ CD25+ Foxp3+ Tregs in the spleen of mice at dpi 3, 7, and 14.  ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001.

Figure 5

Effects of IL-37 on cytokine expression in the liver of MCMV-infected mice (n = 3 − 5 mice in each group). Each colored dot is for the mean value of a group and the vertical lines represent the standard error in a group of mice (n = 3).  ^∗P < 0.05,  ^∗∗P < 0.01,  ^∗∗∗P < 0.001.