These studies will focus on cellular and immune mechanisms of asthma (and sinusitis) as they pertain to aspirin-exacerbated respiratory disease (AERD). Our hypothesis is that AERD contrasts with aspirin tolerant asthma through excessive production of leukotriene E4 (LTE4) acting through specific receptors and a pro- inflammatory interplay with both interleukin (IL)-4 and interferon (IFN)-3. We also hypothesize that aspirin directly induces cellular activation in AERD. AERD is a syndrome consisting of severe persistent asthma, aggressive airway remodeling, extensive hyperplastic eosinophilic sinusitis with nasal polyp (NP) formation, anosmia, and an intolerance to aspirin characterized by symptoms ranging from nasal congestion, rhinorrhea, and wheezing to life-threatening asthma attacks. Aspirin intolerance reflects, in part, increased expression of leukotriene C4 synthase (LTC4S) and cysteinyl leukotriene (CysLT) receptor expression and, as a result, these patients have constitutive overproduction and heightened responsiveness to CysLTs (especially LTE4) with an explosive increase in CysLT production following ingestion of aspirin. We hypothesize that novel receptor(s) recognizing LTE4 are relevant to the pathophysiology of AERD. Our current studies take advantage of having generated an immortalized mast cell line ("LUVA" cells) derived from an AERD donor. These cells preserve relevant features of mast cells including possessing secretory granules containing histamine and surface expression of Fc5RI1. LUVA cells provide a novel model for investigating the previously unexplored molecular basis for direct mast cell activation by aspirin, to which they respond with release of granule contents, Ca+2 fluxes, arachidonate products, and de novo synthesized chemokines. These cells produce a secreted protein that is not any other currently characterized eosinophil-activating factor that acts to promote eosinophil hematopoiesis, survival, and LTC4S expression. We will investigate the interaction of LUVA conditioned medium (LCM) with eosinophils to further define mechanisms central to the pathophysiology of AERD.
Three specific aims are proposed:
Specific Aim 1 will characterize influences of LTE4 acting through LTE4-specific receptors in AERD.
Specific Aim 2 will address the importance of IL-4 and IFN-3 in AERD. Although characterized by profound eosinophilia, cytokines typically associated with eosinophilia (e.g., IL-5) are only modestly and variably expressed in AERD, which instead displays a mixed Th1 (IFN-3)/Th2 (IL-4) cytokine "signature". We will focus on the relatively unexplored role of IFN-3 in promoting eosinophilia and the enhanced LTC4S expression and CysLT secretion that are central to AERD. We will investigate the ability of IFN-3 to render eosinophils responsive to LTE4. And finally, specific aim 3 will characterize LUVA cells and their activation in response to aspirin. In addition, we will define the factor secreted by LUVA cells that enhances eosinophil hematopoiesis and upregulation of LTC4S.
Aspirin-exacerbated respiratory disease (AERD) comprises 5-20% of adult asthmatics and is over-represented among severe asthmatics. Many features of AERD are poorly understood, including the basis for the pathognomonic upregulation of leukotriene production and responsiveness and the mechanism for the cellular activation that occurs after aspirin ingestion. We propose that these leukotrienes act through receptors unique to AERD and they interact with a previously unexplored mast cell-derived protein and IFN-3, features that may prove to be targets for therapeutic modulation.
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