Interleukin‐23 (IL‐23) is a heterodimeric cytokine belonging to the IL‐6/IL‐12 family that plays a key role in several of autoimmune and inflammatory disorders. This family contains the 34 type I cytokine receptor chains and 27 ligands, which share structural and functional similarities, but on the other hand they display distinct roles in shaping Th cells responses. IL‐12 family cytokines have not only proinflammatory effects but they also promote inflammatory responses. IL‐23 is composed of the p40 subunit in common with IL‐12, and with a unique p19 subunit. IL‐23 binding to an IL‐23 receptor expressed on dendritic cells, macrophages and monocytes triggers the activation of Jak2 and Tyk2, which in turn phosphorylates STAT1, STAT3, STAT4 and STAT5 as well as induce formation of STAT3‐STAT4 heterodimers. IL‐23 is one of the essential factors required for the survival and/or expansion of Th17 cells, which produce IL‐17, IL‐17F, IL‐6 and TNF‐α. Th17 cells stimulated by the IL‐23 promote osteoclastogenesis through production of IL‐17, which induce receptor activator of NF‐kappa B ligand on mesenchymal cells. The IL‐23‐IL‐17 axis includes Th17 cells and plays a key role in the development of autoimmune arthritis.

Interleukin (IL)-17 is a 30- to 35-kDa homodimeric polypeptide cytokine cloned in 1993 and originally named cytotoxic T lymphocyte-associated antigen-8 (CTLA-8). Sequencing the human genome resulted in the discovery of an additional five members of the IL-17 family that were consecutively named IL-17B to IL-17F. IL-17A is exclusively produced by a newly identified CD4+ T-helper subset that was recently named Th17. Differentiation of these cells from naive CD4+ T cells requires both TGF-beta and IL-6. IL-15 and, especially, IL-23 are required for these cells' survival and efficient IL-17 production. IL-17 binding to an IL-17 receptor expressed on epithelial, endothelial, and fibroblastic stromal cells triggers the activation of transcription factor NF-kappaB and mitogen-activated protein kinase (p-38), which in turn results in the secretion of IL-1, TNF-alpha, IL-6, IL-8, or prostaglandin E2. The IL-17 family plays a key role in the regulation of immune and inflammatory response, in the homeostasis of several tissues, and the progression of autoimmune diseases. In addition, IL-17 exerts synergistic effects with TNF-alpha and IL-1 in the induction of joint inflammation and cartilage and joint destruction. Given these properties, it is not surprising that in certain pathological conditions, for example rheumatoid arthritis, Th17 cells emerge as a new pathological cell type that, by IL-17 production and release, contributes to their pathogeneses.

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Background T-cell targeted peptide epitope tolerogens from grass pollen allergens may be useful in treating seasonal allergic rhinitis, but there is urgent need for optimisation of approaches from improved understanding of mechanism. Objective We sought to identify human leukocyte antigen (HLA)-DR1-restricted epitopes from the Timothy grass pollen allergen, Phleum pratense, and characterise T-cell immune regulation following intranasal administration of a single, immunodominant epitope. Methods T-cell epitopes within P pratense were identified using HLA-DR1 transgenic mice and tetramer-guided epitope mapping (TGEM) in HLA-DR1-positive individuals with grass allergy. An immunodominant epitope was tested in HLA-DR1 transgenics for impact on responses to whole Phl p5 b or peptide. Microarrays and quantitative PCR were used to characterise T-cell immunity. Results Peptide 26 ( p26) was identified in HLA-DR1 transgenic mice and by TGEM analysis of HLA-DR1-positive individuals with grass allergy. p26 shows promiscuous binding to a wide range of HLA class II alleles, making it of relevance across immunogenetically diverse patients. The epitope is conserved in rye and velvet grass, making it applicable across a spectrum of grass pollen allergy. Intranasal pretreatment of mice with p26 results in significantly reduced T-cell responses. Transcriptomic array analysis in mice showed T-cell regulation in the intranasal treatment group associated with increased expression of members of the Cbl-b and Itch E3 ubiquitin ligase pathway. Conclusions We defined an immunodominant P pratense epitope, p26, with broad binding across multiple HLA class II alleles. Intranasal treatment of mice with p26 results in T-cell regulation to whole allergen, involving the Cbl-b and Itch regulatory pathway.