Abstract
BackgroundSerine proteases in German cockroach (GC) have been shown to mediate allergic airway inflammation through the activation of protease activated receptor (PAR)-2. Neutrophils play an important role in regulating the innate immune response, and are recruited into the airways following GC frass exposure. As such, we investigated the role of PAR-2 in airway neutrophil recruitment, activation and cytokine production following allergen exposure.MethodsWild type and PAR-2-deficient mice were administered a single intratracheal instillation of PBS or GC frass and neutrophil recruitment, expression of PAR-2, CD80, CD86, and MHC class II were assessed by flow cytometry and levels of tumor necrosis factor (TNF)α was assessed by ELISA. Uptake of AlexaFluor 405-labeled GC frass by neutrophils was performed by flow cytometry.ResultsNeutrophil recruitment in the lung and airways following GC frass exposure was significantly decreased in PAR-2-deficient mice compared to wild type mice. GC frass exposure increased the level of PAR-2 on pulmonary neutrophils and increased numbers of PAR-2-positive neutrophils were found in the lungs; however PAR-2 did not play a role in meditating allergen uptake. Comparing wild type and PAR-2-deficient mice, we found that a single exposure to GC frass increased levels of CD80 and CD86 on pulmonary neutrophils, an effect which was independent of PAR-2 expression. Neutrophils isolated from the whole lungs of naïve PAR-2-deficient mice treated ex vivo with GC frass produced significantly less TNFα than in similarly treated wild type neutrophils. Lastly, neutrophils were isolated from the bronchoalveolar lavage fluid of wild type and PAR-2-deficient mice following a single intratracheal exposure to GC frass. Airway neutrophils from PAR-2-deficient mice released substantially decreased levels of TNFα, suggesting a role for PAR-2 in neutrophil-derived cytokine production.ConclusionsTogether these data suggest PAR-2 expression can be upregulated on lung neutrophils following allergen exposure and the consequence is altered release of TNFα which could drive the early innate immune response.
Highlights
Serine proteases in German cockroach (GC) have been shown to mediate allergic airway inflammation through the activation of protease activated receptor (PAR)-2
GC frass induced neutrophil recruitment into the lung To confirm that a single exposure to GC frass induced airway neutrophilia, mice were administered an intratracheal instillation of GC frass and 18 h later, bronchoalveolar lavage (BAL) fluid was harvested
We found that a single exposure to GC frass induced significant neutrophilia in the lungs of wild-type mice, there was considerably less neutrophilia in the BAL fluid from PAR-2-deficient mice (Figure 1A)
Summary
Serine proteases in German cockroach (GC) have been shown to mediate allergic airway inflammation through the activation of protease activated receptor (PAR)-2. Neutrophils play an important role in regulating the innate immune response, and are recruited into the airways following GC frass exposure. We investigated the role of PAR-2 in airway neutrophil recruitment, activation and cytokine production following allergen exposure. In our murine model of German cockroach (GC) feces (frass)-mediated allergic airway inflammation, we find significantly increased levels of neutrophils in the bronchoalveolar lavage (BAL) fluid [4,5]. Others have shown an early and transient increase of neutrophils into the airways following allergen exposure in humans and OVA challenge in mice [6]. Considering the fact that neutrophils play an immediate role in host defense, it seems reasonable that they may be poised to control the events leading up to the generation of adaptive immunity
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