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Cysteinyl leukotrienes (cysLTs), leukotriene C4 (LTC4), LTD4, and LTE4 are proinflammatory lipid mediators with pathobiologic function in asthma. LTE4, the stable cysLT, is a weak agonist for the type 1 and type 2 cysLT receptors (CysLTRs), which constrict airway smooth muscle, but elicits airflow obstruction and pulmonary inflammation in patients with asthma. We recently identified GPR99 as a high-affinity receptor for LTE4 that mediates cutaneous vascular permeability. Here we demonstrate that a single intranasal exposure to extract from the respiratory pathogen Alternaria alternata elicits profound epithelial cell (EpC) mucin release and submucosal swelling in the nasal mucosa of mice that depends on cysLTs, as it is absent in mice deficient in the terminal enzyme for cysLT biosynthesis, LTC4 synthase (LTC4S). These mucosal changes are associated with mast cell (MC) activation and absent in MC-deficient mice, suggesting a role for MCs in control of EpC function. Of the three CysLTRs, only GPR99-deficient mice are fully protected from EpC mucin release and swelling elicited by Alternaria or by intranasal LTE4 GPR99 expression is detected on lung and nasal EpCs, which release mucin to doses of LTE4 one log lower than that required to elicit submucosal swelling. Finally, mice deficient in MCs, LTC4S, or GPR99 have reduced baseline numbers of goblet cells, indicating an additional function in regulating EpC homeostasis. These results demonstrate a novel role for GPR99 among CysLTRs in control of respiratory EpC function and suggest that inhibition of LTE4 and of GPR99 may have therapeutic benefits in asthma.

Aspirin-exacerbated respiratory disease (AERD) is characterized by asthma, tissue eosinophilia, overproduction of cysteinyl leukotrienes (cysLTs), and respiratory reactions to nonselective cyclooxygenase (COX) inhibitors. Ex vivo studies suggest that functional abnormalities of the COX-2/microsomal prostaglandin (PG)E2 synthase-1 system may underlie AERD. We demonstrate that microsomal PGE2 synthase-1 null mice develop a remarkably AERD-like phenotype in a model of eosinophilic pulmonary inflammation. Lysine aspirin (Lys-ASA)-challenged PGE2 synthase-1 null mice exhibit sustained increases in airway resistance, along with lung mast cell (MC) activation and cysLT overproduction. A stable PGE2 analog and a selective E prostanoid (EP)2 receptor agonist blocked the responses to Lys-ASA by ∼90%; EP3 and EP4 agonists were also active. The increases in airway resistance and MC products were blocked by antagonists of the type 1 cysLT receptor or 5-lipoxygenase, implying that bronchoconstriction and MC activation were both cysLT dependent. Lys-ASA-induced cysLT generation and MC activation depended on platelet-adherent granulocytes and T-prostanoid (TP) receptors. Thus, lesions that impair the inducible generation of PGE2 remove control of platelet/granulocyte interactions and TP-receptor-dependent cysLT production, permitting MC activation in response to COX-1 inhibition. The findings suggest applications of antiplatelet drugs or TP receptor antagonists for the treatment of AERD.

Prostaglandin E 2 (PGE 2 ) is an abundant lipid inflammatory mediator with potent but incompletely understood anti-inflammatory actions in the lung. Deficient PGE 2 generation in the lung predisposes to airway hyperresponsiveness and aspirin intolerance in asthmatic individuals. PGE 2 -deficient ptges −/− mice develop exaggerated pulmonary eosinophilia and pulmonary arteriolar smooth-muscle hyperplasia compared with PGE 2 -sufficient controls when challenged intranasally with a house dust mite extract. We now demonstrate that both pulmonary eosinophilia and vascular remodeling in the setting of PGE 2 deficiency depend on thromboxane A 2 and signaling through the T prostanoid (TP) receptor. Deletion of TP receptors from ptges −/− mice reduces inflammation, vascular remodeling, cytokine generation, and airway reactivity to wild-type levels, with contributions from TP receptors localized to both hematopoietic cells and tissue. TP receptor signaling ex vivo is controlled heterologously by E prostanoid (EP) 1 and EP 2 receptor-dependent signaling pathways coupling to protein kinases C and A, respectively. TP-dependent up-regulation of intracellular adhesion molecule-1 expression is essential for the effects of PGE 2 deficiency. Thus, PGE 2 controls the strength of TP receptor signaling as a major bronchoprotective mechanism, carrying implications for the pathobiology and therapy of asthma.

There is a wide variation among humans and mice in airway hyperresponsiveness (AHR) in the absence of allergen sensitization, i.e., naïve AHR. Because mast cell (MC) activation is thought to mediate AHR in atopic asthmatic subjects, we asked whether MCs mediate naïve AHR in A/J mice. We generated an A/J congenic strain lacking c-Kit by introgression of the Wv mutation, which resulted in the elimination of MCs and the abrogation of naïve AHR. Imatinib, which disrupts Kit signaling, also abrogated AHR in A/J mice. Remarkably, introduction of the Vga9 Mitf mutation into the A/J background resulted in the ablation of MCs but did not ameliorate AHR. These results indicate that c-Kit is required for development of AHR in an MC-independent fashion.

Mast cells (MC) are stem cell factor-dependent tissue-based hematopoietic cells with substantial functional heterogeneity. Cord blood-derived human MC (hMC) express functional receptors for IL-5, and IL-5 mediates stem cell factor-dependent comitogenesis of hMCin vitro. Although IL-5 is not required for normal hMC development, we considered that it might prime hMC for their high-affinity Fc receptor for IgE (FcɛRI)-dependent generation of cytokines, as previously demonstrated for IL-4. Compared with hMC maintained in stem cell factor alone, hMC primed with IL-5 expressed 2- to 4-fold higher steady-state levels of TNF-α, IL-5, IL-13, macrophage inflammatory protein 1α, and granulocyte-macrophage colony-stimulating factor transcripts 2 h after FcɛRI crosslinking and secreted 2- to 5-fold greater quantities of the corresponding cytokines, except IL-13, at 6 h. Unlike IL-4, IL-5 priming did not enhance FcɛRI-dependent histamine release. Thus, IL-5 augments cytokine production by hMC by a mechanism distinct from that of IL-4 and with a different resultant profile of cytokine production. These observations suggest a potentially autocrine effect of IL-5 on hMC for amplification of allergic immune responses, in addition to its recognized paracrine effects on eosinophils, and implicate both IL-4 and IL-5 in the modulation of the hMC phenotype.