SUMMARY House dust mite-derived proteases contribute to allergic disorders in part by disrupting epithelial barrier function. Interleukin-33 (IL-33), produced by lung cells after exposure to protease allergens, can induce innate-type airway eosinophilia by activating natural helper (NH) cells, a member of group 2 innate lymphoid cells (ILC2), to secrete Th2 type-cytokines. Because IL-33 also can induce mast cells (MCs) to secrete Th2 type-cytokines, MCs are thought to cooperate with NH cells in enhancing protease or IL-33-mediated innate-type airway eosinophilia. However, we found that MC-deficient KitW-sh/W-sh mice exhibited exacerbated protease-induced lung inflammation associated with reduced numbers of regulatory T (Treg) cells. Moreover, IL-2 produced by IL-33-stimulated MCs promoted expansion of numbers of Treg cells, thereby suppressing development of papain- or IL-33-induced airway eosinophilia. We have thus identified a unique anti-inflammatory pathway that can limit induction of innate-type allergic airway inflammation mediated by NH cells.
BackgroundIL-25, IL-33 and TSLP are produced predominantly by epithelial cells and are known to induce Th2-type cytokines. Th2-type cytokines are involved not only in host defense against nematodes, but also in the development of Th2-type allergic diseases. TSLP was reported to be crucial for development of allergic airway inflammation in mice after inhalation of allergens to which they had been sensitized epicutaneously (EC) beforehand. However, the roles of IL-25 and IL-33 in the setting remain unclear.MethodsMice deficient in IL-25 and IL-33 were sensitized EC with ovalbumin (OVA) and then challenged intranasally with OVA. Airway inflammation, the number of inflammatory cells in bronchoalveolar lavage fluids (BALFs) and airway hyperresponsiveness (AHR) in the mice were determined, respectively, by histological analysis, with a hemocytometer, and by using plethysmograph chambers with a ventilator. Expression of mRNA in the skin and lungs was determined by quantitative PCR, while the BALF levels of myeloperoxidase (MPO) and eosinophil peroxidase (EPO) and the serum levels of IgE were determined by ELISA.Results Normal OVA-specific Th2- and Th17-cell responses of lymph nodes and spleens were observed in IL-25-deficient (IL-25-/-) and IL-33-/- mice after EC sensitization with OVA. Nevertheless, the number of eosinophils, but not neutrophils, in the BALFs, and the levels of Th2 cytokines, but not Th17 cytokines, in the lungs were significantly decreased in the IL-25-/- and IL-33-/- mice pre-sensitized EC with OVA, followed by inhalation of OVA, whereas their levels of AHR and OVA-specific serum IgE were normal.ConclusionsBoth IL-25 and IL-33 are critical for induction of Th2-type cytokine-mediated allergic airway eosinophilia, but not Th17-type cytokine-mediated airway neutrophilia, at the local sites of lungs in the challenge phase of mice sensitized EC with OVA. They do not affect OVA-specific T-cell induction in the sensitization phase.
Chitin, which is a major component of house dust mites (HDM), fungi, crustaceans, etc., can activate immune cells, suggesting that it contributes to development of allergic disorders such as asthma. Although the pathophysiological sensitization route of asthmatic patients to allergens is considered via the respiratory tract, the roles of intranasally-administered chitin in development of asthma remain unclear. After ovalbumin (OVA) challenge, development of airway inflammation was profoundly exacerbated in mice sensitized with OVA in the presence of chitin. The exacerbation was dependent on IL-33, but not IL-25, thymic stromal lymphopoietin or IL-17A. Chitin enhanced IL-33-dependent IL-1β production by dendritic cells (DCs). Furthermore, chitin- and IL-33-stimulated DC-derived IL-1β promoted OVA-specific Th2 cell activation, resulting in aggravation of OVA-induced airway inflammation. These findings indicate the adjuvant activity of chitin via a new mechanism and provide important clues for development of therapeutics for allergic disorders caused by HDM, fungi and crustaceans.
Because intractable itch reduces quality of life, understanding the fundamental mechanisms of itch is required to develop antipruritic treatments. Itch is mediated by peripheral sensory neurons, which originate from the neural crest (nc) during development. itch-associated signaling molecules have been detected in genetically engineered animals and in cultures of peripheral neurons from dorsal root ganglia (DRG). Ethical difficulties collecting peripheral neurons from human DRG have limited analysis of itch in humans. This study describes a method of differentiating peripheral neurons from human induced pluripotent stem cells (hipScs) for physiological study of itch. this method resulted in the robust induction of p75 and HNK1 double-positive NC cells from hiPSCs. The expression of NC markers TFAP2A, SOX10 and SNAI1 increased during NC induction. The induction efficiency was nearly 90%, and human peripheral neurons expressing peripherin were efficiently differentiated from hiPSC-derived NC cells. Moreover, induced peripheral neurons expressed the sensory neuronal marker BRN3A and the itch-related receptors HRH1, MRGPRX1, IL31R and IL-4R. Calcium imaging analyses indicated that these peripheral neurons included sensory neurons responsive to itch-related stimuli such as histamine, BAM8-22, IL-31 and IL-4. These findings may enable detailed analyses of human DRG neurons and may result in new therapies for intractable itch. Somatic sensations, including itch and pain are mediated by primary sensory neurons, which have cell bodies in dorsal root ganglia (DRG) or trigeminal ganglia. These neurons differ in somal size, expression of ion channels and receptors, innervation territories, and electrophysiological properties 1. Small-diameter DRG neurons with unmyelinated axons (C fibers) are the major types that mediate itch and pain 1,2. Similar to pain, chronic and intractable itch reduces quality of life in patients with skin diseases such as atopic dermatitis (AD), which are frequently resistant to conventional treatments, such as histamine H 1 receptor antagonists (antihistamines). Itch in atopic skin is elicited by noxious stimuli, with barrier dysfunction caused by itch-induced scratching, which are associated with the itch-scratch cycle 3. Understanding the fundamental mechanisms of itch is required for the development of antipruritic treatments. Studies in genetically engineered animals and rodent DRG neuron cultures have revealed signaling molecules and receptors that contribute to the induction and transmission of itch. Mas-related G protein-coupled receptors (Mrgprs), especially MrgprAs, MrgprB4, MrgprB5, MrgprC11 and MrgprD, have been reported involved in histamine-independent itch pathways in mice, with the expression of these Mrgprs restricted to small-diameter DRG neurons 4. In humans, MRGPRXs are also selectively expressed in DRG neurons 5. The antimalarial drug chloroquine and bovine adrenal medulla peptide 8-22 (BAM8-22) activate MrgprA3 and MrgprC11, respectively, and elicit itch in mice through a distin...
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