IL-19 and IL-20: two novel cytokines with importance in inflammatory diseases

IL-19 and IL-20 are two cytokines that were discovered in 2000 and 2001, respectively. Based on the structure and location of their genes, their primary and secondary protein structures and the used receptor complexes, they were classified with IL-10, IL-22, IL-24, IL-26, IL-28 and IL-29 in the IL-10 family of cytokines, and form a subgroup with IL-24 within this family. IL-19 and IL-20 are produced by monocytes as well as non-immune tissue cells under inflammatory conditions. IL-19 and IL-20 act via a receptor complex that consists of the IL-20R1 and IL-20R2 chains. IL-20 is additionally able to signal via a second receptor complex (IL-22R1/IL-20R2). It is controversial whether or not IL-19 and IL-20 regulate the function of immune cells. However, the expression of their receptors aliments the perception that the cells of the skin, lungs and reproductive organs as well as various glands are major targets of these mediators. Results from animal experiments and massively increased expression of these mediators in human inflamed tissues support the assumption that they play an important role in the pathogenesis of a few inflammatory diseases. For this reason, the authors have reviewed the facts known at present regarding these cytokines and postulate that IL-19 and IL-20 are pharmacologically interesting distal elements of an inflammatory cascade.     

IL-19 and IL-20: two novel cytokines with importance in inflammatory diseases

IL-19 and IL-20 are two cytokines that were discovered in 2000 and 2001, respectively. Based on the structure and location of their genes, their primary and secondary protein structures and the used receptor complexes, they were classified with IL-10, IL-22, IL-24, IL-26, IL-28 and IL-29 in the IL-10 family of cytokines, and form a subgroup with IL-24 within this family. IL-19 and IL-20 are produced by monocytes as well as non-immune tissue cells under inflammatory conditions. IL-19 and IL-20 act via a receptor complex that consists of the IL-20R1 and IL-20R2 chains. IL-20 is additionally able to signal via a second receptor complex (IL-22R1/IL-20R2). It is controversial whether or not IL-19 and IL-20 regulate the function of immune cells. However, the expression of their receptors aliments the perception that the cells of the skin, lungs and reproductive organs as well as various glands are major targets of these mediators. Results from animal experiments and massively increased expression of these mediators in human inflamed tissues support the assumption that they play an important role in the pathogenesis of a few inflammatory diseases. For this reason, the authors have reviewed the facts known at present regarding these cytokines and postulate that IL-19 and IL-20 are pharmacologically interesting distal elements of an inflammatory cascade.     

Allergic inflammation: role of cytokines with special emphasis on IL-4

This review examines recent articles on the relationship of cytokines to allergy and inflammation with particular emphasis on interleukin (IL)-4. The objective of this article is therefore to review published studies to identify cytokines consistently involved in allergic inflammation. Proinflammatory cytokines, including IL-4, IL-5, IL-13 and GM-CSF along with TNF-alpha play a role in allergen-induced airway leukocyte recruitment and these cytokines can be generated by T mast cells and other cells. In addition, IL-9, IL-25, IL-33, IL-17, IL-27 and IFN-gamma are deeply involved in the regulation of asthma. Blocking the effect of these proinflammatory cytokines might provide new therapeutic approaches for the control of allergy and inflammation.     

IL-17-expressing cells as a potential therapeutic target for treatment of immunological disorders

IL-17 is a multifunctional cytokine produced by activated CD4+ and CD8+ lymphocytes as well as stimulated unconventional Tγδ and natural killer T cells. IL-17 induces expression of chemokines, proinflammatory cytokines and metalloproteinases, thereby stimulating the inflammation and chemotaxis of neutrophils. Elevation of proinflammatory cytokines is associated with asthma and autoimmune disorders, such as multiple sclerosis, rheumatoid arthritis and psoriasis. Although the role of IL-17 in these disorders is not always easy to define, extensive research has demonstrated an aggravating influence of IL-17 in some animal models. Thus, the development of therapeutics to reduce IL-17 levels is a promising strategy for ameliorating inflammatory diseases. This review briefly summarizes recent knowledge about stimulants and intracellular signaling pathways that induce development and maturation of IL-17-expressing cells. Its positive and negative roles on disease progression and its importance in vaccine-induced memory are also discussed. Finally, recent literature describing potential therapeutic approaches for targeting IL-17 is presented.     

IL-37 is protective in allergic contact dermatitis through mast cell inhibition

Allergic contact dermatitis (ACD), characterized predominantly by erythema, vesiculation, and pruritus, is a T cell-mediated skin inflammatory condition. Among immune cells involved in ACD, mast cells (MCs) play an essential role in its pathogenesis. As an inhibitor of proinflammatory IL-1 family members, interleukin 37 (IL-37) has been shown to ameliorate inflammatory responses in various allergic diseases. In this study, we assessed the immunomodulatory effect of IL-37 on allergic inflammation using a 2,4-dinitrofluorobenzene (DNFB)-induced ACD rat model and isolated rat peritoneal mast cells (RPMCs). Systematic application of IL-37 significantly relieved ear swelling, reduced inflammatory cell infiltration, decreased inflammatory cytokine production (TNF-α, IL-1β, IFN-γ, and IL-13), inhibited MC recruitment, lowered IgE levels, and reduced IL-33 production in the local ear tissues with DNFB challenge. Additionally, RPMCs isolated from ACD rats with IL-37 intervention showed downregulation of IL-6, TNF-α, IL-13, and MCP-1 production following IL-33 stimulation, and reduction of β-hexosaminidase and histamine release under DNP-IgE/HSA treatment. Moreover, IL-37 treatment also significantly restrained NF-κB activation and P38 phosphorylation in ACD RPMCs. SIS3, a specific Smad3 inhibitor, abolished the suppressive effects of IL-37 on MC-mediated allergic inflammation, suggesting the participation of Smad3 in the anti-ACD effect of IL-37. These findings indicated that IL-37 protects against IL-33-regulated MC inflammatory responses via inhibition of NF-κB and P38 MAPK activation accompanying the regulation of Smad3 in rats with ACD.     

IL-31 a Th2 cytokine involved in immunity and inflammation

Cytokines are immunal regulatory proteins, however they also play a relevant role in inflammatory diseases. IL-31 is a newly discovered cytokine expressed primarily in TH2 cells, introduced by activated CD4+ T cells. IL-31 is capable of inducing chemokines and other cytokines in several inflammatory diseases via its surface receptor. This cytokine is also produced by mast cells and mast cell line, suggesting a role in allergic diseases. In this editorial we revisit the biological role of IL-31 in immunity and inflammation.     

IL-19 as a potential therapeutic in autoimmune and inflammatory diseases

Interleukin-19 (IL-19) is a member of the IL-10 family of cytokines. The last ten years from the finding of IL-19, investigations underline the role of IL-19 in the immunological diseases. It is known that expression of IL-19 is increased in the epidermis of patients with psoriasis, which is a Th1 dominant disease. Increased concentration of IL-19 has also been found in the serum of patients with asthma, which is a Th2 dominant disease. There is an increasing body of data demonstrating that IL-19 is associated with the pathogenesis of both Th1 and Th2 dominant diseases. Regarding the role of IL-19 on the innate immunity and inflammation, interestingly, in vitro studies have shown that lipopolysaccharide can stimulate human monocytes and macrophages to upregulate the expression of IL-19. IL- 19 is upregulated in macrophages after infection and lessens inflammation by suppressing the production of tumor necrosis factor-α , IL-6 and IL-12, but not by inducing IL-10. In addition, IL-19-deficient mice are susceptible to experimental colitis induced by dextran sodium sulfate, a disease which is characterized by excessive inflammatory responses of local macrophages and epithelial cells to intestinal microflora. In this review, we discuss our current understanding of the role of IL-19 in autoimmune and inflammatory diseases.     

A role for CB2 receptors in anandamide signalling pathways involved in the regulation of IL-12 and IL-23 in microglial cells

The endocannabinoid system represents a novel therapeutic target for autoimmune and chronic inflammatory diseases. IL-12 and IL-23 are functionally related heterodimeric cytokines that play a crucial role in the pathogenesis of multiple sclerosis (MS). In the present study we investigated the effects of the endocannabinoid anandamide (AEA) on the inducible expression of the biologically active cytokines IL-12p70 and IL-23, and their forming subunits, in activated microglial cells. We also studied the signalling pathways involved in the regulation of IL-12p70/IL-23 expression and addressed the possible interactions of AEA with these pathways. Here, we show that AEA was capable to inhibit the production of biologically active IL-12p70 and IL-23, and their subunits, by activated human and murine microglial cultures. Treatment of activated microglial cells with inhibitors of several mitogen-activated protein kinase (MAPK) reveals that AEA acts through the ERK1/2 and JNK pathways to down-regulate IL-12p70 and IL-23. These effects were partially mediated by CB2 receptor activation. Together, our results provide the first demonstration of a role of AEA in inhibiting IL-12p70/IL-23 axis in human and murine microglial cells via the CB2 receptor and suggest that the pharmacological manipulation of the endocannabinoid system is a potential tool for treating brain inflammatory and autoimmune diseases, like MS.     

Targeting IL-17 in autoimmunity and inflammation

The discovery of two distinct subsets of helper T cells, IFN-γ-producing Th1 cells and IL-4-producing Th2 cells, about three decades ago enabled us to understand the immunopathology of cell-mediated and allergic inflammatory diseases in humans. The observation that T cell-mediated experimental autoimmune diseases can be induced in mice lacking Th1 and Th2 cell responses prompted many immunologists to hypothesize that there might be additional subsets in helper T cell population which mediate autoimmunity in the absence of Th1 and Th2 cells. Consequently, multiple independent research groups identified IL-17-expressing RORγt⁺CD4⁺ T cell population as a distinct subset of helper T cells which promotes autoimmune tissue inflammation. Subsequent studies have revealed that innate immune cells, including γδ T cells, NKT cells and innate lymphoid cells, also produce type 17 cytokines and contribute to tissue inflammation. In this review, we discuss our current understanding on the biology of IL-17 and the therapeutic potential of targeting IL-17 for the treatment of immune disorders in humans.     

IL-27 and autoimmune rheumatologic diseases: The good,the bad,and the ugly

The footprint of cytokines is evident in almost every biological process, such as development, as well as the pathogenesis of the different diseases, immune responses to pathogens, etc. These small proteins are categorized into different functional classes; for instance, they can play a pro-inflammatory or anti-inflammatory role in different situations, or they can confer a polarization to the immune system. Interleukin (IL)-27 is a member of the IL-12 family. Antigen-presenting cells are the primary source of IL-27 production, which exerts its effects by bindings to the IL-27 receptor expressed on the surface of target cells. Interaction of IL-27 and IL-27 receptor leads to activation of the JAK-STAT and p38 MAPK signaling pathways. Most studies focused on the inflammatory effects of this cytokine, but gradually anti-inflammatory effects were also revealed for this cytokine, which changed the traditional perception of the function of this cytokine. The functionality of IL-27 in the pathogenesis of rheumatic diseases has been attributed to a double-blade sword. Hence, novel therapeutic approaches have been devised targeting IL-12 family that has been accompanied with promising results. In this review, we focused on the inflammatory and anti-inflammatory properties of IL-27 in different autoimmune rheumatologic diseases and its plausible therapeutic potentials.     

IL-17 cytokine/receptor families: emerging targets for the modulation of inflammatory responses

IL-17 was identified a decade ago as a pro-inflammatory cytokine produced by activated T cells that stimulates the secretion of other cytokines from various non-lymphoid cells by acting through a unique cell surface receptor, IL17R. Evidence that IL-17 may contribute to several immune-mediated diseases, such as rheumatoid arthritis and airway inflammation, prompted much interest in this cytokine. Recently, the large-scale analysis of expressed sequence tags (EST) led to the discovery of novel genes dispersed in the human genome that encode at least five additional cytokines structurally related to IL-17. Screening of EST databases also uncovered at least four novel genes encoding Type I transmembrane proteins with significant homology to IL-17R, thereby forming a family of receptors whose cognate ligands are likely to belong to the IL-17 cytokine family. Initial characterisation of some of these cytokines and one IL-17R homologue demonstrated their involvement in regulating inflammatory responses in a manner similar to, albeit distinct from, that of prototypic IL-17. The IL-17 cytokine/receptor families appear therefore to represent unique signalling systems within the cytokine network that might offer innovative approaches to manipulate immune and inflammatory responses. The prospect of targeting these molecules for therapeutic purposes has generated a substantial volume of patent literature that will be reviewed here.     

Utilizing IL-12, IL-15 and IL-7 as Mucosal Vaccine Adjuvants

In this paper we review and discuss three of the most exciting and promising cytokines for therapeutic intervention and immunomodulation of immune responses including those on mucosal surfaces. The main properties of IL-12, IL-15 and IL-7 are described and the studies utilizing these cytokines as immunomodulators and vaccine adjuvants discussed.     

A new target for the treatment of inflammatory bowel disease: Interleukin-37

Interleukin (IL)-37 belongs to the IL-1 cytokine family. It has anti-inflammatory effects on numerous autoimmune diseases such as asthma, psoriasis, inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE), multiple sclerosis (MS) and rheumatoid arthritis (RA). Mechanistically, IL-37 plays an anti-inflammatory role by regulating the expression of inflammatory factors in two ways: binding extracellular receptors IL-18R or transferring into the nucleus with Smad3. IBD is a kind of idiopathic intestinal inflammatory disease with unknown etiology and pathogenesis. Recent researches had proved that IL-37 is negatively involved in the pathogenesis and development of IBD. Among various inflammatory diseases, IL-37 has been shown to regulate inflammatory development by acting on various immune cells such as neutrophils, macrophages (Mϕ), dendritic cells (DCs), T cells and intestinal epithelial cells. This review summarizes the biological role of IL-37, and its immunoregulatory effects on the immune cells, especially anti-inflammatory function in both human and experimental models of IBD.     

Targeting the IL-1 family members in skin inflammation

The IL-1 family of cytokines comprises 11 proteins with pro- and anti-inflammatory functions that are mediated through an equally large group of receptors and coreceptors. Dysregulation of the IL-1 system may lead to diseases such as psoriasis, atopic dermatitis, contact dermatitis and cutaneous lupus erythematosus. These inflammatory skin conditions greatly affect quality of life and life expectancy, and their frequencies are increasing. However, treatment options for these diseases are unsatisfactory. This review briefly summarizes new findings, reported in the past 2 years, implicating IL-1 family members in skin inflammation. Furthermore, how the biological activities of the IL-1 family members may be inhibited is discussed.     

Luteolin suppresses IL-31 production in IL-33-stimulated mast cells through MAPK and NF-κB signaling pathways

IL-31 and IL-33 are cytokines, which are expressed in many inflammatory and pathological disorders, thus suggesting an IL-31/IL-33 axis interaction in pathological diseases. Luteolin from natural products is known for its anti-inflammatory activities associated with the regulation of inflammatory signaling pathways. Here, we investigated the effects of luteolin in the regulation of IL-33-stimulated production and secretion of IL-31 in HMC-1.2 mast cells. Human mast cells (HMC-1.2) were treated with luteolin and stimulated with IL-33. Real-time PCR was used to measure IL-31 mRNA expression. Western blot and immunofluorescence assays were used to measure IL-31 expression. ELISA techniques were used to measure IL-31 secretion and NF-κB-DNA-binding activities. The results revealed that luteolin inhibited the expression of IL-31 in IL-33-stimulated HMC-1.2 cells at the mRNA and protein levels. Also, Luteolin inhibited the secretion of IL-31 into the cell culture media of the IL-33-stimulated HMC-1.2 cells. Further findings demonstrated that luteolin inhibited the activation of ERK, JNK, p38, and NF-κB p65 in the IL-33-stimulated HMC-1.2 cells. In addition, luteolin also prevented the nuclear translocation and binding of p65 to its DNA-binding site. Based on the results, luteolin may be considered as a potential therapeutic or functional food agent for the prevention and/or treatment of IL-31 and IL-33-related diseases.     

A bis-malonic acid fullerene derivative significantly suppressed IL-33-induced IL-6 expression by inhibiting NF-κB activation

IL-33 functions as a ligand for ST2L, which is mainly expressed in immune cells, including mast cells. IL-33 is a potent inducer of pro-inflammatory cytokines, such as IL-6, and has been implicated in the pathogenesis of allergic inflammatory diseases. Therefore, IL-33 has recently been attracting attention as a new target for the treatment of inflammatory diseases. In the present study, we demonstrated that a water-soluble bis-malonic acid fullerene derivative (C₆₀-dicyclopropane-1,1,1′,1′-tetracarboxylic acid) markedly diminished the IL-33-induced expression of IL-6 in bone marrow-derived mast cells (BMMC). The bis-malonic acid fullerene derivative suppressed the canonical signaling steps required for NF-κB activation such as the degradation of IκBα and nuclear translocation of NF-κB by directly inhibiting the IL-33-induced IKK activation. Although p38 and JNK also contributed to IL-33-induced expression of IL-6, the bis-malonic acid fullerene derivative did not affect their activation. Furthermore, the bis-malonic acid fullerene derivative had no effect on the NF-κB activation pathway induced by TNFα and IL-1. These results suggest that the bis-malonic fullerene derivative has potential as a specific drug for the treatment of IL-33-induced inflammatory diseases by specifically inhibiting the NF-κB activation pathway.     

Interleukin-21 (IL-21) controls inflammatory pathways in the gut

In both Crohn's disease (CD) and ulcerative colitis (UC), the major forms of inflammatory bowel diseases (IBD) in humans, the pathologic process consists of an aberrant local immune response to components of the bacterial microflora, due to abnormally strong effector cell activity that is poorly controlled by counter-regulatory mechanisms. There is also evidence that mucosal immune cells actively interact with non-immune cells to promote tissue damage, and that cytokines are essential mediators of this cross-talk. Interleukin-21 (IL-21), the latest member of the common gamma-chain-dependent cytokine family, is a product of activated CD4+ T cells and natural killer T cells. IL-21 is produced in excess in CD tissue, where it helps sustain the ongoing Th1 inflammation. High IL-21 production occurs also in the inflamed colon of most patients with UC, a disease that is not associated with a marked Th1 cell response. This suggests that, in the gut, IL-21 can modulate additional inflammatory pathways other than enhancing Th1 cell immunity. Indeed, IL-21 stimulates the secretion of extracellular matrix degrading enzymes by fibroblasts, and of the T cell chemoattractant, MIP-3 alpha, by epithelial cells. These data collectively indicate that IL-21 is a mediator of the chronic inflammatory response in CD and UC, and suggest that IL-21 may be an emerging therapeutic target in IBD.     

Regulation of mast cell development by inflammatory factors

Mast cells are potent effectors playing a key role in IgE-associated hypersensitivity reactions, allergic disorders, inflammation and protective immune responses. Mast cell development in vivo occurs mainly in non-hematopoietic microenvironments and increased mast cell numbers can be seen in various inflammatory diseases and pathologic conditions. SCF (also known as kit ligand or KitL) and c-kit signaling are essential for both human and murine mast cell development, while IL-3 is required for murine mast cell hyperplasia that occurs in response to various stimuli. Besides SCF and IL-3, the cytokines IL-4, IL-9, IL-10 and IL-13 are also called mast cell growth factors due to their actions synergistically promoting mast cell proliferation and differentiation in the presence of SCF or IL-3. These cytokines alone however are unable to support neither the proliferation nor survival of mast cells. Most research has focused on examining the direct effects of the above cytokines on mast cells or their precursors. However, it is difficult to explain the process of mast cell development only in terms of the above mast cell growth factors. A series of experiments in our laboratory and by others has revealed that inflammatory mediators and cytokines, as triggers or regulators, are also crucial for mast cell development. This review summarizes recent progress in our understanding of how various inflammatory factors regulate mast cell development, with particular focus on the effects of prostaglandin E (PGE), TNF-alpha, IL-6, IFN-gamma and an unknown apoptosis-inducing factor produced by IL-4-stimulated macrophages.