SolubleIL-33; Biomarker; Immunity; Diseases; Hepatitis.

Arshad MI, Khan HA, Piquet-Pellorce C, Samson M (2016) Interleukin-33 and its Soluble Receptor ST2 as Non-Invasive Biomarkers of Human Hepatitis. JSM Hepat 1(1): 1003.

The cytokine interleukin-33 (IL-33) is a member of IL-1 family described in 2005 with pluripotent functions in various diseases and wide spectrum of target immune cells in tissues [1]. In human, IL-33 is encoded on chromosome 9 and full length IL33 is synthesized from two mRNA transcripts translating into one IL-33 protein composing of 270 amino acids [2]. Evolving data evidenced “two lives” of IL-33 due to its unique nuclear localization as nuclear repressor and extracellular cytokine functions (danger signal, immune defense, tissue repair and skewing of T helper cell responses). Primarily, IL-33 was reported to be present in tissue barrier cells (vascular endothelial cells, epithelial cells) as guardian of barriers but later on it was found to be localized/expressed by parenchymal cells such as astrocytes, adipocytes and hepatocytes [3]. The release of IL-33 as an “alarmin” from these cells was described to be linked with cellular demise (apoptosis, necrosis, necroptosis) by infection, injury, mechanical stress or trauma. In contrast to alarmin functions, the expression of IL-33 was associated with chronic diseases as well. Therefore, IL-33 evolved as a biomarker of acute and chronic diseases.As reviewed recently, the extracellular IL33 is prone to cleavage by enzymes such as caspases-(1/3/7), elastase, chymase, calpain and cathepsin G which limits the alarmin signals and degrades the biological activity of IL-33 [3,4]. Another study demonstrated inactivation of IL-33 by structural changes or formation of disulfide bonds upon oxidation of IL-33 protein molecule [5]. The extracellular cytokine functions of IL33 are orchestrated by interaction with dimeric IL-1RAcP/ST2L receptors. The IL-33 specific ST2-receptor is mainly expressed by immune cells such as Th2 cells, nuocytes/innate lymphoid cells (ILCs), granulocytes, macrophages and CD8 T cells [3,4]. The soluble ST2 (sST2) receptor acts as decoy receptor of IL-33 and it abrogates the activity of circulating IL-33. However, the level of sST2 was associated with various diseases as indicator of disease proces.

In human liver pathology, we first evidenced the overexpression of IL-33 in liver sinusoidal endothelial cells and vascular endothelial cells in fibrotic human livers [6]. Accumulating data demonstrated association of circulating levels of IL-33 or sST2 with clinical human liver diseases which poised the role of soluble IL-33/ST2 as biomarkers of hepatitis to discern different stages of hepatitis. Serum IL-33was elevated in human patients (mean values) of acute liver failure (~190 pg/ml), acuteon-chronic liver failure (~200 pg/ml) and chronic liver failure (~110 pg/ml) than healthy control (HC) (~25 pg/ml) [7]. In a cohort of HC and chronic hepatitis C (CHC) patients in Italy, IL33 level was raised in CHC (350-430 ng/ml) than HC (30-60 ng/ ml), moreover, IL-33 level (180-320 ng/ml) varied in early stage of liver fibrosis (F1-F2 METAVIR score) than late stage (F3-F4) of fibrosis (450-550 ng/ml) [8]. Post antiviral treated patients showed lower level of IL-33 in serum indicating a prognostic value of IL-33 (8).Up-regulated circulating level of IL-33 was found in chronic hepatitis B (30-70 pg/ml)and CHC (210-900 pg/ml) affected Chinese patients than HC (10-25 pg/ml) which lowered to 20 pg/ml following 12 weeks of antiviral therapy [9,10]. In hepatocellular carcinoma (HCC) patients, serum IL-33 level raised during metastasis (137 pg/ml mean value) or preoperative HCC (116 pg/ml) than non-metastatic conditions (8 pg/ml) or HC (4 pg/ml) individuals [11]. In infants with biliary atresia, IL-33 increased in sera of children (791 pg/ml) than HC infants (588 pg/ml) and it positively correlated withgammaglutamyl transferase level [12]. In visceral leishmaniasis (hepatotropic parasite) infection in human, the IL-33 level was up-regulated (41 pg/ml) than HC (8 pg/ml) [13] suggesting IL33 as a marker of wide range of liver diseases. The IL-33 level was significantly increased (57-75 pg/m) in sera of primary biliary cirrhosis patients than HC (32 pg/ml) suggesting IL-33 a diagnostic marker of biliary disease [14]. In HBV infected acuteon-chronic liver failure (ACLF) human patients, the serum IL-33 was raised (313 pg/ml) than chronic hepatitis B (97 pg/ml) or HC (28 pg/ml) groups highlighting the use of IL-33 to discern different stages of viral hepatitis [15]. In chronic HBV infection and in ACLF, significantly higher IL-33 serum concentration was detected (14 pg/ml; 17 pg/ml respectively) compared to HC (5 pg/ml), however, in this study the level of soluble IL-33 was lower than other studieswhich may be associated with inclusion of more male patients in this study or difference of ELISA kit used [16,17]. In patients with HCC in Germany, serum IL-33 level (1079 pg/ml) was raised in comparison to HC (218 pg/ml) but not in liver cirrhosis (203 pg/ml), however, IL-33 level in HCC was higher due to HCV or alcohol abuse than HBV infection [18].

The serum sST2 was elevated in human patients (mean values) of acute liver failure (~1910 pg/ml), acute-on-chronic liver failure (~1750 pg/ml) and chronic liver failure (~280 pg/ml) than HC (~50 pg/ml) [7]. In HCC and liver cirrhosis patients sST2 level was up-regulated (741 pg/ml; 1653 pg/ml respectively) than HC (38 pg/ml) [18] with non-significant difference in level of sST2 during HCC/liver cirrhosis induced by HBV, HCV or alcohol [18]. The sST2 level in serum was significantly raised in chronic HBV and HCV patients (12500 pg/ml; 2000-2400 pg/ ml respectively) than HC (900-1000 pg/ml) indicating the differential expression with type of viral infection [9,10]. The soluble sST2 level predicted mortality in HBV related ACLF in a cohort of Chinese population with increased sST2 concentration in ACLF (94 ng/ml) and chronic HBV infection (19 ng/ml) than HC (9 ng/ml), however, the level of soluble IL-33 did not vary in these groups [19]. The sST2 level was significantly augmented (1343- 1439 pg/ml) in sera of primary biliary cirrhosis patients than HC (144 pg/ml) revealing sST2 as good indicator of biliary disease [14]. In HBV infected ACLF patients, sST2 was raised (1545 pg/ml) than chronic hepatitis B (152 pg/ml) or HC (149 pg/ml) groups highlighting sST2 differentiating marker of viral hepatitis [15]. In liver fibrosis caused by HBV, significantly increased level of sST2 (1133 pg/ml) predicted the progression of liver fibrosis in comparison to HC (762 pg/ml) individuals [20]

The ELISA based clinical data strongly evidenced that soluble IL-33 or sST2 can be used as non-invasive diagnostic or prognostic biomarkers of liver diseases. However, variation in results of serum IL-33/sST2 concentration is associated with type of viral hepatitis, liver pathology or stage of liver disease. In future, further studies and considerations of sensitivity, specificity, reproducibility and widespread availability (nonpatented) will be needed to finally accredit the IL-33/sST2 as biomarkers of hepatitis.

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3. Martin NT, Martin MU. Interleukin 33 is a guardian of barriers and a local alarmin. Nat Immunol. 2016; 17: 122-131.

4. Arshad MI, Khan HA, Noel G, Piquet-Pellorce C, Samson M. Potential Therapeutic Aspects of Alarmin Cytokine Interleukin 33 or Its Inhibitors in Various Diseases. Clin Ther. 2016.

5. Cohen ES, Scott IC, Majithiya JB, Rapley L, Kemp BP, England E, et al. Oxidation of the alarmin IL-33 regulates ST2-dependent inflammation. Nat Commun. 2015; 6: 8327.

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7. Roth GA, Zimmermann M, Lubsczyk BA, Pilz J, Faybik P, Hetz H, et al. Up-regulation of interleukin 33 and soluble ST2 serum levels in liver failure. J Surg Res. 2010; 163: e79-83.

8. Cacopardo B, Rita Pinzone M, Palermo F, Nunnari G. Changes in serum Interleukin-33 concentration before and after treatment with pegylated interferon alfa-2a plus ribavirin in patients with chronic hepatitis C genotype 1b infection. Hepat Mon. 2012; 12: 7611.

9. Wang J, Cai Y, Ji H, Feng J, Ayana DA, Niu J, et al. Serum IL-33 levels are associated with liver damage in patients with chronic hepatitis B. J Interferon Cytokine Res. 2012; 32: 248-253.

10. Wang J, Zhao P, Guo H, Sun X, Jiang Z, Xu L, et al. Serum IL-33 levels are associated with liver damage in patients with chronic hepatitis C. Mediators Inflamm. 2012; 2012: 819636.

11. Zhang P, Liu XK, Chu Z, Ye JC, Li KL, Zhuang WL, et al. Detection of interleukin-33 in serum and carcinoma tissue from patients with hepatocellular carcinoma and its clinical implications. J Int Med Res. 2012; 40: 1654-1661.

12. Dong R, Dong K, Wang X, Chen G, Shen C, Zheng S. Interleukin-33 overexpression is associated with gamma-glutamyl transferase in biliary atresia. Cytokine. 2013; 61: 433-437.

13. Rostan O, Gangneux JP, Piquet-Pellorce C, Manuel C, McKenzie AN, Guiguen C, et al. The IL-33/ST2 axis is associated with human visceral leishmaniasis and suppresses Th1 responses in the livers of BALB/c mice infected with Leishmania donovani. MBio. 2013; 4: 00383-13.

14. Sun Y, Zhang JY, Lv S, Wang H, Gong M, Du N, et al. Interleukin-33 promotes disease progression in patients with primary biliary cirrhosis. Tohoku J Exp Med. 2014; 234: 255-261.

15. Gao S, Huan SL, Han LY, Li F, Ji XF, Li XY, et al. Overexpression of serum sST2 is associated with poor prognosis in acute-on-chronic hepatitis B liver failure. Clin Res Hepatol Gastroenterol. 2015; 39: 315-323.

16. Yu X, Guo R, Ming D, Deng Y, Su M, Lin C, et al. The Transforming Growth Factor beta1/Interleukin-31 Pathway Is Upregulated in Patients with Hepatitis B Virus-Related Acute-on-Chronic Liver Failure and Is Associated with Disease Severity and Survival. Clin Vaccine Immunol. 2015; 22: 484-492.

17. Ming D, Yu X, Guo R, Deng Y, Li J, Lin C, et al. Elevated TGF-beta1/IL-31 Pathway Is Associated with the Disease Severity of Hepatitis B VirusRelated Liver Cirrhosis. Viral Immunol. 2015; 28: 209-216.

18. Bergis D, Kassis V, Ranglack A, Koeberle V, Piiper A, Kronenberger B, et al. High Serum Levels of the Interleukin-33 Receptor Soluble ST2 as a Negative Prognostic Factor in Hepatocellular Carcinoma. Transl Oncol. 2013; 6: 311-318.

19. Lei Z, Mo Z, Zhu J, Pang X, Zheng X, Wu Z, et al. Soluble ST2 plasma concentrations predict mortality in HBV-related acute-on-chronic liver failure. Mediators Inflamm. 2015; 2015: 535938.

20. Oztas E, Kuzu UB, Zengin NI, Kalkan IH, Onder FO, Yildiz H, et al. Can Serum ST2 Levels Be Used as a Marker of Fibrosis in Chronic Hepatitis B Infection? Medicine (Baltimore). 2015; 94: 1889.