More recently, the TNF family cytokine TL1A was also implicated in ILC2 activation (Yu et al

More recently, the TNF family cytokine TL1A was also implicated in ILC2 activation (Yu et al., 2014). treatment of airways disease. Introduction Type 2, Benznidazole or allergic, inflammation in the lung requires the cytokines IL-5, IL-13, and IL-9, which collectively elicit eosinophilia, alternative activation of macrophages, goblet cell hyperplasia, smooth muscle hypercontractility, and tissue remodeling, and may contribute to Benznidazole wound healing (Licona-Limn et al., 2013; Gour and Wills-Karp, 2015). As long-lived tissue-resident cells, group 2 innate lymphoid cells (ILC2s) are a critical early source of these type 2 cytokines before type 2 helper T cell (Th2 cell) recruitment. The role of ILC2s in promoting type 2 lung inflammation has been established in mice using models such as parasitic worm infection, chitin, papain, fungal, or house dust mite challenge, and allergic asthma (Neill et al., 2010; Price et al., 2010; Barlow et al., 2012; Bartemes et al., 2012; Halim et al., 2012; Klein Wolterink et al., 2012; Van Dyken et al., 2014). In humans, ILC2s accumulate in nasal polyps of patients with chronic sinusitis (Mj?sberg et al., 2011; Ho et al., 2015), and genome-wide association studies have implicated the ILC2-activating cytokine IL-33 in airways disease (Ober and Yao, 2011). The mechanisms of ILC2 activation upon encounter of a type 2 agonist remain incompletely understood. Because Th2 cells and ILC2s require the same transcription factors for their differentiation and secrete many of the same cytokines, our extensive understanding of gene regulation in Th2 cells may be informative for ILC2 biology. In Th2 cells, signaling through the TCR activates a phospholipase C (PLC)Cdependent signaling cascade that drives three primary responses: (1) cytosolic Ca2+ influx, calcineurin activation, and translocation of NFAT into the nucleus, (2) MAPK-dependent translocation of activator protein 1 (AP-1) to the nucleus, and (3) protein kinase C (PKC)Cdependent activation of NF-B. In Benznidazole the nucleus, NFAT, AP-1, and NF-B cooperatively drive expression of type 2 cytokines (Hermann-Kleiter and Baier, 2010). In contrast, ILC2s lack antigen receptors and instead integrate numerous locally produced signals to drive cytokine production. We hypothesize that in doing so, ILC2s respond to perturbations in tissue homeostasis that are common to the diverse set of type 2 agonists (von Moltke and Locksley, 2014). To date, most studies have focused on the ILC2-activating cytokines thymic stromal lymphopoietin, IL-33, and IL-25, of which AXIN2 IL-33 is particularly important in the lung (Barlow et al., 2013). More recently, the TNF family cytokine TL1A was also implicated in ILC2 activation (Yu et al., 2014). Notably, although these signals can activate AP-1 and NF-B (Parnet et al., 1996; Brint et al., 2002), none have been linked to rapid cytosolic Ca2+ flux. Therefore, whether calcineurin and NFAT contribute to ILC2 activation remains an open question. Eicosanoids are a family of arachidonic acid metabolites that includes the prostaglandins and leukotrienes (LTs). Eicosanoids are rapidly synthesized and degraded and are potent drivers of inflammation that act on numerous target cells. For example, LT signaling induces contraction of smooth muscle, chemokine production in mast cells, and permeabilization of vasculature. Eicosanoid biosynthesis is initiated by phospholipase A2, which releases arachidonic acid from membrane phospholipids (Fig. S1 A). Arachidonic acid then serves as the substrate for the cyclooxygenase enzymes, leading to prostaglandin production, or for 5-lipoxygenase (ALOX5), which catalyzes the first step in all LT synthesis by generating LTA4. LTA4 is rapidly converted to LTB4 by LTA4 hydrolase or to LTC4 by LTC4 synthase (LTC4S), which conjugates glutathione. Peptidase cleavages convert LTC4 to LTD4 and then LTE4, and these three LTs are collectively known as the cysteinyl LTs (cysLTs). Both LTB4 and the cysLTs bind G proteinCcoupled receptors. LTB4R1 is the primary LTB4 receptor and in immune cells predominantly mediates chemotaxis. LTB4R2 binds LTB4 with much lower affinity and can respond to other arachidonic acid metabolites as well (Yokomizo et al., 2001). CYSLTR1 is the Benznidazole best-characterized cysLT receptor, and in transfected cells, it exhibits the following ligand preference: LTD4 LTC4 LTE4. Like the TCR, CYSLTR1 signals through PLC to induce Ca2+ flux and activate PKC (Peres et al., 2007). CYSLTR2 expressed in transfected cells binds LTD4 and LTC4 with equal affinity, but like CYSLTR1, it does not bind strongly to LTE4 (Heise et al., 2000; Laidlaw and Boyce, 2012). The high-affinity LTE4 receptor was recently identified.