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Interleukin-22(IL-22) is a member of a group of the IL-10 family, a class of potent mediators of cellular inflammatory-responses. IL-22 is produced by activated DC and T cells. IL-22 and IL-10 receptor chains play a role in cellular targeting and signal transduction. It can initiate and regulate innate immune responses against bacterial pathogens especially in epithelial cells such as respiratory and gut epithelial cells. IL-22 along with IL-17 likely plays a role in the coordinated response of both adaptive and innate immune systems. IL-22 also promotes hepatocyte survival in the liver and epithelial cells in the lung and gut similar to IL-10. Biological activity of IL-22 is initiated by binding to a cell-surface complex consisting of IL-22R1 and IL-10R2 receptor chains. IL-22 biological activity is further regulated by interactions with a soluble binding protein, IL-22BP. IL-22BP and an extracellular region of IL-22R1 share sequence similarity. In some cases, the pro-inflammatory versus tissue-protective functions of IL-22 are regulated by cytokine IL-17A.

Usage

IL-22 can exhibit anti-inflammation effects at the inflammed site, thus protect which from further inflammatory damage.

In our project, IL-22 is expected to inhibit the local inflammation on liver that is induced by the excessive intake of alcohol, and perform protective effect on liver[1]. At the same time, IL-22 can promote regeneration of damaged liver thus restore liver function to certain degree [2].

Biology

IL-22 is a member of the IL-10 family and is primarily a cytokine secreted by Th22 cells [3].

The production of TNF-α by macrophages is significantly increased in patients with alcoholic hepatitis, and this is further exacerbated by exogenous LPS, resulting in significant inflammation of the liver. In addition, LPS decreased the level of IL-22 production by macrophages through the JNK signaling pathway [4]. Taken together, this leads to apoptosis of hepatocytes.

IL-22 reduces inflammation through the JAK-STAT pathway as well as the NF-κB pathway to inhibit TNF-α production, reducing hepatocyte apoptosis and protecting hepatocytes [5].

Characterization

We constructed a secretory expression vector for IL-22, using E.coli as chasis. IL-22 was detected using an ELISA kit.

Figure 1.Result of activity assay using human IL-22 ELISA kit.

(A1/B1) are blank-corrected wells. Wells (A2/B2), (A3/B3), (A4/B4), (A5/B5), (A6/B6), (A7/B7), (A8/B8) are standard human IL-22 protein sample with concentration at 2000pg/ml, 1000pg/ml, 500pg/ml, 250pg/ml, 150pg/ml, 62.5pg/ml and 0pg/ml respectively. Wells C1-C3 are duplicate wells for protein sample 1 while C4-C6 are duplicate wells for protein sample 2. C7-C8 are negative control wells. Protein sample 1 was induced by adding 1M IPTG, and protein sample 2 was induced by adding 0.5M. No induction agent was added to the negative control group.

Figure 2.Standard curve of human IL-22.

Table 1

Table 2

Table 1&2 Result of activity assay using human IL-22 ELISA kit.

The protein expression of protein sample 1 is approximately 5.43ng/ml, while sample 2 is approximately 3.094ng/ml.

Figure 3.Comparison of Corrected A450 of Sample Groups.

Both sample groups were significantly different compared to the negative control group.*P < 0.05, ** P < 0.01, *** P < 0.001, and ****P < 0.0001 by t test.

Figure 4.Comparison of the levels of TNF-α produced by different groups.

We examined the TNF-α reducing efficacy of IL-22 standard samples and the culture supernatant of our engineered bacteria which contains secreted IL-22 protein for a concentration about 5ng/ml (analyzed by ELISA test). As can be seen, both groups of IL-22 significantly inhibited the production of TNF-α and were significantly different from the negative control group (without IL-22).*P < 0.05, ** P < 0.01, *** P < 0.001, and ****P < 0.0001 by t test.

Reference

[1] Kong, X., Feng, D., Mathews, S. & Gao, B. Hepatoprotective and anti-fibrotic functions of interleukin-22: therapeutic potential for the treatment of alcoholic liver disease [J]. Gastroenterol. Hepatol. 28,56–60(2013).

[2] Park O, Wang H, Weng H, et al. In vivo consequences of liver specific interleukin-22 expression in mice: Implications for human liver disease progression [J]. Hepatology, 2011 54(1): 252-261.

[3] Shabgah A G , Navashenaq J G , Shabgah G , et al. Interleukin-22 in human inflammatory diseases and viral infections.[J]. Autoimmunity Reviews, 2017:S1568997217302549.

[4] Liu Y, Verma VK, Maihi H, et al. Lipopolysaccharide downregulates macrophage-derived IL-22 to modulate alcohol-induced hepatocyte cell death [J]. Am J Physiol Cell Physiol，2017,313(3): C305-C313.

[5] Radaeva S, Sun R, Pan HN, Hong F, Gao B. Interleukin 22 (IL-22) plays a protective role in T cell-mediated murine hepatitis: IL-22 is a survival factor for hepatocytes via STAT3 activation [J]. Hepatology, 2004; 39: 1332-1342.

Sequence and Features