Hypoxic modulation of hepatocyte responses to the cytokine interleukin-22

Interleukin-22 protects from endotoxemia by inducing suppressive F4/80+Ly6GhiLy6Chi cells population

Background

Excessive inflammatory response is the primary cause of early death in patients with endotoxemia. Interleukin 22 (IL-22) has been shown to play critical roles in the modulation of infectious diseases, but its function in regulating immune responses during endotoxemia remains unclear.

Methods

Lipopolysaccharide (LPS) was used to induce endotoxemia mouse model with or without a recombinant fusion protein containing human IL-22 (F-652). IL-6, TNF-α, IL-1β, and MCP-1 were measured by ELISA assays. The type of macrophage was assessed by flow cytometry. Real-time PCR was used to detect the expression of S100A9.

Results

We found that F-652 injection significantly improved the survival rates and reduced pro-inflammatory cytokines (IL-6, TNF-a, IL-1β, MCP-1) in LPS-induced endotoxemia mice. However, the mice injected with F-652 had a higher number of infiltrated immune cells after LPS treatment, suggesting an impaired immune response. Flow cytometry analysis showed a higher number of F4/80⁺Ly6G^hiLy6C^hi cells that highly expressed M2-like macrophage markers (Ym1, Arg, CCL17) in the peritoneal cavity of the F-652-treated endotoxemia mice. Further investigation found that these suppressive M2 macrophages might be induced by F-652 since the F-652 treatment could increase S100A9 in vitro.

Conclusions

Our study suggests that IL-22 has a protective role against endotoxemia by inducing the development of immunosuppressive cells through S100A9.

IL-18/IL-18BP and IL-22/IL-22BP: Two interrelated couples with therapeutic potential

Interleukin (IL)-18 and IL-22 are key components of cytokine networks that play a decisive role in (pathological) inflammation, host defense, and tissue regeneration. Tight regulation of cytokine-driven signaling, inflammation, and immunoactivation is supposed to enable nullification of a given deleterious trigger without mediating overwhelming collateral tissue damage or even activating a cancerous face of regeneration. In fact, feedback regulation by specific cytokine opponents is regarded as a major means by which the immune system is kept in balance. Herein, we shine a light on the interplay between IL-18 and IL-22 and their opponents IL-18 binding protein (IL-18BP) and IL-22BP in order to provide integrated information on their biology, pathophysiological significance, and prospect as targets and/or instruments of therapeutic intervention.

IL-22: There Is a Gap in Our Knowledge

IL-22 is a critical cytokine in modulating tissue responses during inflammation. IL-22 is upregulated in many chronic inflammatory diseases, making IL-22 biology a potentially rewarding therapeutic target. However, this is complicated by the dual-natured role of IL-22 in inflammation, as the cytokine can be protective or inflammatory depending on the disease model. Although scientific interest in IL-22 has increased considerably in the past 10 y, there is still much we do not know about the environmental, cellular, and molecular factors that regulate the production and function of this cytokine. A better understanding of IL-22 biology will allow us to develop new or improved therapeutics for treating chronic inflammatory diseases. In this article, I will highlight some of the outstanding questions in IL-22 biology.

Excessive Iron Availability Caused by Disorders of Interleukin-10 and Interleukin-22 Contributes to High Altitude Polycythemia

Background: Because the pathogenesis of high altitude polycythemia (HAPC) is unclear, the aim of the present study was to explore whether abnormal iron metabolism is involved in the pathogenesis of HAPC and the possible cause. Methods: We examined the serum levels of iron, total iron binding capacity, soluble transferrin receptor (sTfR), ferritin, and hepcidin as well as erythropoietin (EPO) and inflammation-related cytokines in 20 healthy volunteers at sea level, 36 healthy high-altitude migrants, and 33 patients with HAPC. Mice that were exposed to a simulated hypoxic environment at an altitude of 5,000 m for 4 weeks received exogenous iron or intervention on cytokines, and the iron-related and hematological indices of peripheral blood and bone marrow were detected. The in vitro effects of some cytokines on hematopoietic cells were also observed. Results: Iron mobilization and utilization were enhanced in people who had lived at high altitudes for a long time. Notably, both the iron storage in ferritin and the available iron in the blood were elevated in patients with HAPC compared with the healthy high-altitude migrants. The correlation analysis indicated that the decreased hepcidin may have contributed to enhanced iron availability in HAPC, and decreased interleukin (IL)-10 and IL-22 were significantly associated with decreased hepcidin. The results of the animal experiments confirmed that a certain degree of iron redundancy may promote bone marrow erythropoiesis and peripheral red blood cell production in hypoxic mice and that decreased IL-10 and IL-22 stimulated iron mobilization during hypoxia by affecting hepcidin expression. Conclusion: These data demonstrated, for the first time, that an excess of obtainable iron caused by disordered IL-10 and IL-22 was involved in the pathogenesis of some HAPC patients. The potential benefits of iron removal and immunoregulation for the prevention and treatment of HAPC deserve further research.