SummaryBackground Basophils are important effector cells involved in the pathogenesis of inflammatory skin diseases including chronic urticaria which is associated by increased IL-31 serum levels. So far the effects of IL-31 on human basophils are unknown. Objective To analyse the functional role of IL-31 in basophil biology. Methods IL-31 expression was evaluated in skin samples derived from chronic spontaneous urticaria patients. Oncostatin M receptor (OSMR), IL-31 receptor A (RA) and IL-31 protein expressions were analysed on human basophils from healthy donors. Basophil responses to IL-31 were assessed for chemotaxis, externalization of CD63 and CD203c as well as the release of histamine, IL-4 and IL-13. Results IL-31RA and OSMR were expressed on human basophils. IL-31 was strongly expressed in the skin of patients with chronic spontaneous urticaria and was released from isolated basophils following either anti-IgE, IL-3 or fMLP stimulation. IL-31 induced chemotaxis and the release of IL-4 and IL-13 which was specifically inhibited by anti-IL-31RA and anti-OSMR. Conversely, IL-31 had no effect on CD63 and CD203c externalization or histamine release. Conclusions and Clinical Relevance Human basophils are a source of -and are activated by -IL-31 with the release of pro-inflammatory cytokines and the induction of chemotaxis indicating an important novel function of IL-31 in basophil biology.

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Bullous pemphigoid (BP) is characterized by substantial skin and blood eosinophilia as well as intensive pruritus. Since the pruritogenic cytokine interleukin (IL)-31 is increased in inflammatory skin diseases the aim of this study was to determine whether IL-31 plays a role in BP. Using immunofluorescence, IL-31 expression was analysed in eosinophils derived from blister fluids and skin from patients with BP and IL-31 levels in blister fluids, serum and culture supernatants were determined by enzyme-linked immunoassay (ELISA). High levels of IL-31 expression were observed in BP blister fluids, but they were only marginally elevated in BP serum compared with healthy controls. Eosinophils from either BP blister fluids or skin biopsies showed strong expression of IL-31. Furthermore, peripheral blood eosinophils from patients with BP, but not healthy controls, released high levels of IL-31, reflecting those in blister fluids. In conclusion, eosinophils are a major source of IL-31 in BP and this cytokine may contribute to itch in patients with BP.

Reference genes (RG) as sample internal controls for gene transcript level analyses by quantitative RT-PCR (RT-qPCR) must be stably expressed within the experimental range. A variety of in vitro cell culture settings with primary human hepatocytes, and Huh-7 and HepG2 cell lines, were used to determine candidate RG expression stability in RT-qPCR analyses. Employing GeNorm, BestKeeper and Normfinder algorithms, this study identifies PSMB6, MDH1 and some more RG as sufficiently unregulated, thus expressed at stable levels, in hepatocyte-like cells in vitro. Inclusion of multiple RG, quenching occasional regulations of single RG, greatly stabilises gene expression level calculations from RT-qPCR data. To further enhance validity and reproducibility of relative RT-qPCR quantifications, the ΔCT calculation can be extended (e-ΔCT) by replacing the CT of a single RG in ΔCT with an averaged CT-value from multiple RG. The use of two or three RG - here identified suited for human hepatocyte-like cells - for normalisation with the straightforward e-ΔCT calculation, should improve reproducibility and robustness of comparative RT-qPCR-based gene expression analyses.

Background: Pruritus is a major symptom of atopic dermatitis (AD) and is transmitted by a subpopulation of non-myelinated C-type free nerve endings in the epidermis and upper dermis. Stimulation of these nerve terminals is affected by histamine, neurotrophins and physical factors. Eosinophils of patients with AD are a source of neurotrophins, including brain-derived neurotrophic factor (BDNF), levels of which correlate with disease severity.Objective: The purpose of this study was to determine the anatomical localization of eosinophils in the skin of patients with AD with regard to peripheral nerves and to investigate whether eosinophils induce sprouting and neurite outgrowth in murine sensory neurons.Methods: Cryosections of skin derived from AD and control (NA) patients were subjected to immunofluorescence analysis with markers for eosinophils, BDNF and neuronal cells. Stimulated eosinophil supernatants were used for the treatment of cultured peripheral mouse dorsal root ganglia (DRG) neurons followed by morphometric analysis.Results: Dermal axon density and the proximity of eosinophils to nerve fibres were significantly higher in AD patients vs NA. Both neuronal projections and eosinophils expressed BDNF. Furthermore, activated eosinophil supernatants induced BDNFdependent mouse DRG neuron branching. Conclusions and Clinical Relevance:Our results indicate that BDNF-positive eosinophils are also localized in close proximity with nerve fibres in AD, suggesting a functional relationship between BDNF-expressing eosinophils and neuronal projections.These observations suggest that eosinophils may have considerable impact on pruritus by supporting sensory nerve branching. K E Y W O R D S atopic dermatitis, BDNF, DRG neurons, eosinophilsThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.