Triggering NETosis via protease-activated receptor (PAR)-2 signaling as a mechanism of hijacking neutrophils function for pathogen benefits.

Neutrophil-derived networks of DNA-composed extracellular fibers covered with antimicrobial molecules, referred to as neutrophil extracellular traps (NETs), are recognized as a physiological microbicidal mechanism of innate immunity. The formation of NETs is also classified as a model of a cell death called NETosis. Despite intensive research on the NETs formation in response to pathogens, the role of specific bacteria-derived virulence factors in this process, although postulated, is still poorly understood. The aim of our study was to determine the role of gingipains, cysteine proteases responsible for the virulence of P. gingivalis, on the NETosis process induced by this major periodontopathogen. We showed that NETosis triggered by P. gingivalis is gingipain dependent since in the stark contrast to the wild-type strain (W83) the gingipain-null mutant strain only slightly induced the NETs formation. Furthermore, the direct effect of proteases on NETosis was documented using purified gingipains. Notably, the induction of NETosis was dependent on the catalytic activity of gingipains, since proteolytically inactive forms of enzymes showed reduced ability to trigger the NETs formation. Mechanistically, gingipain-induced NETosis was dependent on proteolytic activation of protease-activated receptor-2 (PAR-2). Intriguingly, both P. gingivalis and purified Arg-specific gingipains (Rgp) induced NETs that not only lacked bactericidal activity but instead stimulated the growth of bacteria species otherwise susceptible to killing in NETs. This protection was executed by proteolysis of bactericidal components of NETs. Taken together, gingipains play a dual role in NETosis: they are the potent direct inducers of NETs formation but in the same time, their activity prevents P. gingivalis entrapment and subsequent killing. This may explain a paradox that despite the massive accumulation of neutrophils and NETs formation in periodontal pockets periodontal pathogens and associated pathobionts thrive in this environment.

The Transient Receptor Potential Channel Vanilloid 1 Is Critical in Innate Airway Epithelial Responses to Protease Allergens.

The airway epithelium plays a critical role in innate responses to airborne allergens by secreting IL-1 family cytokines such as IL-1α and IL-33 as alarmins that subsequently orchestrate appropriate immune responses. Previous studies revealed that epithelial IL-33 secretion by allergens such as Alternaria alternata or house dust mite involves Ca2+-dependent signaling, via initial activation of ATP-stimulated P2YR2 (type 2 purinoceptor) and subsequent activation of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase DUOX1. We sought to identify proximal mechanisms by which epithelial cells sense these allergens and here highlight the importance of PAR2 (protease-activated receptor 2) and TRP (transient receptor potential) Ca2+ channels such as TRPV1 (TRP vanilloid 1) in these responses. Combined studies of primary human nasal and mouse tracheal epithelial cells, as well as immortalized human bronchial epithelial cells, indicated the importance of both PAR2 and TRPV1 in IL-33 secretion by both Alternaria alternata and house dust mite, based on both pharmacological and genetic approaches. TRPV1 was also critically involved in allergen-induced ATP release, activation of DUOX1, and redox-dependent activation of EGFR (epidermal growth factor receptor). Moreover, genetic deletion of TRPV1 dramatically attenuated allergen-induced IL-33 secretion and subsequent type 2 responses in mice in vivo. TRPV1 not only contributed to ATP release and P2YR2 signaling but also was critical in downstream innate responses to ATP, indicating potentiating effects of P2YR2 on TRPV1 activation. In aggregate, our studies illustrate a complex relationship between various receptor types, including PAR2 and P2YR2, in epithelial responses to asthma-relevant airborne allergens and highlight the central importance of TRPV1 in such responses.

A role for mast cells and mast cell tryptase in driving neutrophil recruitment in LPS-induced lung inflammation via protease-activated receptor 2 in mice.

OBJECTIVE: This study aims to investigate the role of protease-activated receptor (PAR) 2 and mast cell (MC) tryptase in LPS-induced lung inflammation and neutrophil recruitment in the lungs of C57BL/6 mice. METHODS: C57BL/6 mice were pretreated with the PAR2 antagonist ENMD-1068, compound 48/80 or aprotinin prior to intranasal instillation of MC tryptase or LPS. Blood leukocytes, C-X-C motif chemokine ligand (CXCL) 1 production leukocytes recovered from bronchoalveolar lavage fluid (BALF), and histopathological analysis of the lung were evaluated 4 h later. Furthermore, we performed experiments to determine intracellular calcium signaling in RAW 264.7 cells stimulated with LPS in the presence or absence of a protease inhibitor cocktail or ENMD-1068 and evaluated PAR2 expression in the lungs of LPS-treated mice. RESULTS: Pharmacological blockade of PAR2 or inhibition of proteases reduced neutrophils recovered in BALF and LPS-induced calcium signaling. PAR2 blockade impaired LPS-induced lung inflammation, PAR2 expression in the lung and CXCL1 release in BALF, and increased circulating blood neutrophils. Intranasal instillation of MC tryptase increased the number of neutrophils recovered in BALF, and MC depletion with compound 48/80 impaired LPS-induced neutrophil migration. CONCLUSION: Our study provides, for the first time, evidence of a pivotal role for MCs and MC tryptase in neutrophil migration, lung inflammation and macrophage activation triggered by LPS, by a mechanism dependent on PAR2 activation.

Neutrophilia, gelatinase release and microvascular leakage induced by human mast cell tryptase in a mouse model: Lack of a role of protease-activated receptor 2 (PAR2).

BACKGROUND: Tryptase, the most abundant protease of the human mast cell, has been implicated as a key mediator of allergic inflammation that acts through activation of PAR2. OBJECTIVES: To investigate the contribution of PAR2 in the pro-inflammatory actions mediated by tryptase in a mice model. METHODS: We have injected recombinant human ßII-tryptase into the peritoneum of PAR2-deficient and wild-type C57BL/6 mice. After 6, 12 and 24 hours, mice were killed, peritoneal lavage performed and inflammatory changes investigated. RESULTS: Tryptase stimulated an increase in neutrophil numbers in the peritoneum, but responses did not differ between PAR2-deficient and wild-type mice. Heat inactivation of tryptase or pre-incubation with a selective tryptase inhibitor reduced neutrophilia, but neutrophil accumulation was not elicited with a peptide agonist of PAR2 (SLIGRL-NH2 ). Zymography indicated that tryptase stimulated the release of matrix metalloproteinases (MMP) 2 and 9 in the peritoneum of both mouse strains. Studies involving immunomagnetic isolation of neutrophils suggested that neutrophils represent the major cellular source of tryptase-induced MMP2 and MMP9. At 24 hours after tryptase injection, there was increased microvascular leakage as indicated by high levels of albumin in peritoneal lavage fluid, and this appeared to be partially abolished by heat-inactivating tryptase or addition of a protease inhibitor. There was no corresponding increase in levels of histamine or total protein. The extent of tryptase-induced microvascular leakage or gelatinase release into the peritoneum did not differ between PAR2-deficient and wild-type mice. CONCLUSIONS: Our findings indicate that tryptase is a potent stimulus for neutrophil accumulation, MMP release and microvascular leakage. Although these actions required an intact catalytic site, the primary mechanism of tryptase in vivo would appear to involve processes independent of PAR2.

Immediate-type allergic and protease-mediated reactions are involved in scratching behaviour induced by topical application of Dermatophagoides farinae extract in NC/Nga mice.

Atopic dermatitis (AD)-like dermatitis can be induced by repeated topical application of an ointment containing Dermatophagoides farinae body (Dfb) extract in NC/Nga mice. This AD-like murine model also exhibits a biphasic increase in the number of scratching behaviour after topical application of Dfb ointment. In this study, we investigated the possible mechanisms underlying the scratching behaviour in each phase. An increase in the content of mast cell-derived mediators such as histamine and 5-hydroxytryptamine in the lesional skin and increased vascular permeability were observed in the early phase after the Dfb ointment application. Chlorpheniramine (H1 receptor antagonist) and cromoglycate (mast cell stabilizer) reduced the scratching behaviour in the early phase but not that in the later phase. Furthermore, the content of various endogenous pruritogens such as interleukin-31 and thymic stromal lymphopoietin in the lesional skin was increased 1 or 24 hours after the Dfb ointment application. Elevated expression of proteinase-activated receptor-2 (PAR-2) was also observed in the epidermis. Finally, gabexate (serine protease inhibitor) reduced the scratching behaviour in both phases, and anti-PAR2 antibody also showed a tendency to reduce both scratching behaviours. These findings suggest that immediate-type allergic reactions caused by mast cell degranulation and PAR-2 activation by proteases are involved in the scratching behaviour in this AD-like model.

Proteinase-activated receptor-2 blockade inhibits changes seen in a chronic murine asthma model.

BACKGROUND: Proteinase-Activated Receptor-2 (PAR2 ) is a G protein-coupled receptor activated by serine proteinases. We have shown that PAR2 activation in the airways is involved in the development of allergic inflammation and airway hyperresponsiveness (AHR) in acute murine models. We hypothesized that functional inhibition of PAR2 prevents allergic inflammation, AHR and airway remodeling in chronic allergic airway inflammation models. MATERIAL AND METHODS: We developed and used a 12 week model of cockroach extract (CE)-mediated AHR, airway inflammation and remodeling in BALB/c mice. RESULTS: Mice sensitized and challenged with CE for 12 weeks exhibit AHR, increased numbers of eosinophils in bronchoalveolar lavage (BAL) and increased collagen content in the lung tissue compared to saline controls. Administration of an anti-PAR2 antibody, SAM-11, after the initial development of airway inflammation significantly inhibited all these parameters. CONCLUSIONS: Our data demonstrate that PAR2 signaling plays a key role in CE-induced AHR and airway inflammation/remodeling in long term models of allergic airway inflammation. Targeting PAR2 activation may be a successful therapeutic strategy for allergic asthma.

Serine protease allergen favours Th2 responses via PAR-2 and STAT3 activation in murine model.

BACKGROUND: Protease activity of Per a 10 favours Th2 responses by differential regulation of IL-12p70 and IL-23 cytokine subunits. This study aimed to elucidate the underlying mechanism of differential regulation of IL-12p70 and IL-23. METHODS: PAR-2 activation was blocked in murine model by administering SAM11 before each sensitization. CD11c+ p-STAT3+ cells were measured in lungs by flow cytometry. BMDCs were pretreated with SAM11 or isotype control or stattic and stimulated with Per a 10. p-STAT3 levels were measured using Western blot. Transcript levels of IL-12p35, IL-12/23p40 and IL-23p19 were measured using RT-PCR. Cytokine levels were analysed using ELISA. RESULTS: Protease activity of Per a 10 increased p-STAT3 levels in mouse lungs, which was reduced upon PAR-2 blockage. Percentage of p-STAT3+ CD11c+ cells was higher in Per a 10-administered mice and was reduced upon PAR-2 blockage. IL-12p35 and IL-12p70 levels were higher, and IL-23p19 and IL-23 levels were lower in both SAM11-treated mice and BMDCs indicating a role of PAR-2-mediated signalling. IL-4, TSLP, IL-17A, EPO activity, total cell count and specific IgE and IgG1 levels were lower in SAM11-administered mice. Inhibiting STAT3 activation via stattic also leads to lower levels of IL-23p19 and IL-23 and higher levels of IL-12p35. CONCLUSIONS: Per a 10 leads to PAR-2 activation on BMDCs resulting in downstream activation of STAT3 to regulate the balance between IL-12/IL-23 subunits causing a cytokine milieu rich in IL-23 to favour Th2 polarization.

House Dust Mites Induce Production of Endothelin-1 and Matrix Metalloproteinase-9 in Keratinocytes via Proteinase-Activated Receptor-2 Activation.

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by skin barrier dysfunction and abnormal immune response. House dust mites (HDM) are a major source of allergens, some of which have cysteine and serine protease activities. Keratinocytes stimulated by HDM-derived proteases have been suggested to contribute to the pathogenesis of AD by producing various cytokines. However, whether keratinocytes contribute to the induction of pruritus in AD, especially by producing pruritus-related mediators upon stimulation with HDM-derived proteases, has not been fully elucidated. METHODS: We examined whether the production of endothelin-1 (ET-1), matrix metalloproteinase (MMP)-2, and MMP-9 in keratinocytes can be induced by stimulation with Dermatophagoides farinae extracts, and if so, whether pretreatment with a protease inhibitor or proteinase-activated receptor-2 (PAR-2) antagonist affects the production of these mediators in keratinocytes. RESULTS: Although MMP-2 levels were undetectable in the culture supernatants, the production of ET-1 and MMP-9 was increased upon stimulation with HDM extracts in a concentration- and time-dependent manner and suppressed by pretreatment of HDM extracts with serine protease inhibitor, but not with cysteine protease inhibitor. Mite-derived serine proteases also induced ET-1 and MMP-9 production in a concentration- and time-dependent manner. Moreover, pretreatment with a PAR-2 antagonist inhibited the production of ET-1 and MMP-9 in keratinocytes. CONCLUSION: These results suggest that the activation of PAR-2 on keratinocytes by HDM-derived serine proteases induces the production of ET-1 and MMP-9, and may contribute to the induction of pruritus in AD.

Protease-activated receptor 2 contributes to Toxoplasma gondii-mediated gut inflammation.

Toxoplasma gondii is a widespread intracellular parasite, which naturally enters the organism via the oral route and crosses the intestinal barrier to disseminate. In addition to neuronal and ocular pathologies, this pathogen also causes gut inflammation in a number of animals. This infection-triggered inflammation has been extensively studied in the C57BL/6 mice, highlighting the importance of the immune cells and their mediators in the development of gut pathology. However, despite their importance in inflammation, the role of protease-activated receptors (PAR) was never reported in the context of T.gondii-mediated small intestine inflammation. Using genetically modified mice, we show that PAR2 plays a pathogenic role in the development of gut inflammatory lesions. We find that PAR2 controls the innate inflammatory mediators IL-6, KC/CXCL1, PGE2 as well as neutrophil infiltration in T. gondii-triggered gut damage. These results bring new knowledge on the mechanisms operating in the gut in response to T. gondii infection.

Role of Aspergillus fumigatus in Triggering Protease-Activated Receptor-2 in Airway Epithelial Cells and Skewing the Cells toward a T-helper 2 Bias.

Aspergillus fumigatus (AF) infection and sensitization are common and promote Th2 disease in individuals with asthma. Innate immune responses of bronchial epithelial cells are now known to play a key role in determination of T cell responses upon encounter with inhaled pathogens. We have recently shown that extracts of AF suppress JAK-STAT signaling in epithelial cells and thus may promote Th2 bias. To elucidate the impact of AF on human bronchial epithelial cells, we tested the hypothesis that AF can modulate the response of airway epithelial cells to favor a Th2 response and explored the molecular mechanism of the effect. Primary normal human bronchial epithelial (NHBE) cells were treated with AF extract or fractionated AF extract before stimulation with poly I:C or infection with human rhinovirus serotype 16 (HRV16). Expression of CXCL10 mRNA (real-time RT-PCR) and protein (ELISA) were measured as markers of IFN-mediated epithelial Th1-biased responses. Western blot was performed to evaluate expression of IFN regulatory factor-3 (IRF-3), NF-κB, and tyrosine-protein phosphatase nonreceptor type 11 (PTPN11), which are other markers of Th1 skewing. Knockdown experiments for protease-activated receptor-2 (PAR-2) and PTPN11 were performed to analyze the role of PAR-2 in the mechanism of suppression by AF. AF and a high-molecular-weight fraction of AF extract (HMW-AF; > 50 kD) profoundly suppressed poly I:C- and HRV16-induced expression of both CXCL10 mRNA and protein from NHBE cells via a mechanism that relied upon PAR-2 activation. Both AF extract and a specific PAR-2 activator (AC-55541) suppressed the poly I:C activation of phospho-IRF-3 without affecting activation of NF-κB. Furthermore, HMW-AF extract enhanced the expression of PTPN11, a phosphatase known to inhibit IFN signaling, and concurrently suppressed poly I:C-induced expression of both CXCL10 mRNA and protein from NHBE cells. These results show that exposure of bronchial epithelial cells to AF extract suppressed poly I:C and HRV16 signaling via a mechanism shown to involve activation of PAR-2 and PTPN11. This action of AF may promote viral disease exacerbations and may skew epithelial cells to promote Th2 inflammation in allergic airway disorders mediated or exacerbated by AF, such as asthma and chronic rhinosinusitis.

Effect of the house dust mite allergen Der p 1 on tryptase release from human mast cells.

This study aimed to investigate the effects of the house dust mite allergen Der p 1 on the secretion of tryptase from the human mast cell line HMC-1. Flow cytometry was used to determine the expression levels of protease-activated receptor-2 (PAR2) on the surface of HMC-1 cells. HMC-1 cells were treated with Der p 1, SLIGRL-NH2 (PAR2 agonist), LRGILS-NH2 (control peptide for PAR2), or Der p 1 + FSLLRY (PAR2 antagonist), and the tryptase levels were measured using enzyme-linked immunosorbent assay. The biological functions of PAR2 were determined using the calcium green indicator, and intracellular calcium fluorescence intensity in the different groups (Der p 1, SLIGRL-NH2, LRGILS- NH2, Der p 1 + FSLLRY, tryptase, tryptase + FSLLRY, or cell culture medium) was detected by laser scanning confocal microscopy. The mast cells expressed PAR2 receptor on their surfaces. Der p 1 alone induced a significant release of intracellular calcium and tryptase in HMC-1 cells compared with the SLIGRL- NH2 treatment group and the control group. The combination of Der p 1 and FSLLRY partly inhibited intracellular calcium and tryptase release in HMC-1 cells compared with the Der p 1 treatment group. Moreover, tryptase induced a significant release of intracellular calcium in the HMC-1 cells. Der p 1 induced HMC-1 cell degranulation and the release of tryptase by activating the PAR2 receptor on the cell surfaces. Tryptase activated the PAR2 receptor and induced intracellular calcium release from the HMC-1 cells in a positive feedback loop.

Proteinase activated receptor-2-mediated dual oxidase-2 up-regulation is involved in enhanced airway reactivity and inflammation in a mouse model of allergic asthma.

Airway epithelial cells (AECs) express a variety of receptors, which sense danger signals from various aeroallergens/pathogens being inhaled constantly. Proteinase-activated receptor 2 (PAR-2) is one such receptor and is activated by cockroach allergens, which have intrinsic serine proteinase activity. Recently, dual oxidases (DUOX), especially DUOX-2, have been shown to be involved in airway inflammation in response to Toll-like receptor activation. However, the association between PAR-2 and DUOX-2 has not been explored in airways of allergic mice. Therefore, this study investigated the contribution of DUOX-2/reactive oxygen species (ROS) signalling in airway reactivity and inflammation after PAR-2 activation. Mice were sensitized intraperitoneally with intact cockroach allergen extract (CE) in the presence of aluminium hydroxide followed by intranasal challenge with CE. Mice were then assessed for airway reactivity, inflammation, oxidative stress (DUOX-2, ROS, inducible nitric oxide synthase, nitrite, nitrotyrosine and protein carbonyls) and apoptosis (Bax, Bcl-2, caspase-3). Challenge with CE led to up-regulation of DUOX-2 and ROS in AECs with concomitant increases in airway reactivity/inflammation and parameters of oxidative stress, and apoptosis. All of these changes were significantly inhibited by intranasal administration of ENMD-1068, a small molecule antagonist of PAR-2 in allergic mice. Administration of diphenyliodonium to allergic mice also led to improvement of allergic airway responses via inhibition of the DUOX-2/ROS pathway; however, these effects were less pronounced than PAR-2 antagonism. The current study suggests that PAR-2 activation leads to up-regulation of the DUOX-2/ROS pathway in AECs, which is involved in regulation of airway reactivity and inflammation via oxidative stress and apoptosis.

Granulocyte-macrophage colony-stimulating factor primes interleukin-13 production by macrophages via protease-activated receptor-2.

Chronic inflammation is often linked to the presence of type 2-polarized macrophages, which are induced by the T helper type 2 cytokines interleukin-4 and interleukin-13 (IL-13). IL-13 is a key mediator of tissue fibrosis caused by T helper type 2-based inflammation. Human neutrophil elastase (HNE) plays a pivotal role in the pathogenesis of pulmonary fibrosis. This study investigated the priming effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on IL-13 expression by macrophages stimulated with HNE. Adherent macrophages were obtained from primary cultures of human mononuclear cells. Expression of IL-13 mRNA and protein by GM-CSF-dependent macrophages was investigated after stimulation with HNE, using the polymerase chain reaction and enzyme-linked immunosorbent assay. GM-CSF had a priming effect on IL-13 mRNA and protein expression by macrophages stimulated with HNE, while this effect was not observed for various other cytokines. GM-CSF-dependent macrophages showed a significant increase in the expression of protease activated receptor-2 (PAR-2) mRNA and protein. The response of IL-13 mRNA to HNE was significantly decreased by pretreatment with alpha1-antitrypsin, a PAR-2 antibody (SAM11), or a PAR-2 antagonist (ENMD-1068). These findings suggest that stimulation with HNE can induce IL-13 production by macrophages, especially GM-CSF-dependent macrophages. Accordingly, neutrophil elastase may have a key role in fibrosis associated with chronic inflammation.

Mechanism of interleukin-13 production by granulocyte-macrophage colony-stimulating factor-dependent macrophages via protease-activated receptor-2.

BACKGROUND: Granulocyte-macrophage colony-stimulating factor (GM-CSF) promotes classically activated M1 macrophages. GM-CSF upregulates protease-activated receptor-2 (PAR-2) protein expression and activation of PAR-2 by human neutrophil elastase (HNE) regulates cytokine production. AIM: This study investigated the mechanism of PAR-2-mediated interleukin (IL)-13 production by GM-CSF-dependent macrophages stimulated with HNE. METHODS: Adherent macrophages were obtained from primary cultures of human mononuclear cells. After stimulation with HNE to activate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway, IL-13 mRNA and protein levels were assessed by the reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS: PAR-2 protein was detected in GM-CSF-dependent macrophages by Western blotting. Unexpectedly, PD98059 (an ERK1 inhibitor) increased IL-13 production, even at higher concentrations. Interestingly, U0126 (an ERK1/2 inhibitor) reduced IL-13 production in a concentration-dependent manner. Neither SB203580 (a p38alpha/p38beta inhibitor) nor BIRB796 (a p38gamma/p38delta inhibitor) affected IL-13 production, while TMB-8 (a calcium chelator) diminished IL-13 production. DISCUSSION: Stimulation with HNE promoted the production of IL-13 (a Th2 cytokine) by GM-CSF-dependent M1 macrophages. PAR-2-mediated IL-13 production may be dependent on the Ca(2+)/ERK2 signaling pathway.

Discovery of 2-aryloxy-4-amino-quinazoline derivatives as novel protease-activated receptor 2 (PAR2) antagonists.

Protease-activated receptor 2 (PAR2) is a member of G protein-coupled receptor and its activation initiates diverse inflammatory responses. Recent studies suggest that antagonists of PAR2 may provide a novel therapeutic strategy for inflammatory diseases. In this study, we have developed a series of 2-aryloxy-4-amino-quinazoline derivatives as PAR2 antagonists and examined their effects against LPS-induced inflammatory responses in RAW 264.7 macrophages. Among these derivatives, compound 2f displayed the greatest antagonistic activity with the IC50 value of 2.8µM. Binding modes of the newly identified PAR2 antagonists were analyzed by molecular docking using IFD/MM-GBSA methods in the putative binding site of PAR2 homology model. Moreover, 2f demonstrated significant inhibitory effects on the LPS-activated pro-inflammatory mediators including nitric oxide (NO), prostaglandin E2 (PGE2), interleukin-1ß (IL-1ß), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) through the regulation of various intracellular signaling pathways involving nuclear factor-κB (NF-κB), activator protein 1 (AP-1) and the mitogen-activated protein kinases (MAPK). Furthermore, administration of 2f significantly reduced the mortality of LPS-induced sepsis in mice. These results provide useful insights into the development of novel PAR2 antagonists with anti-inflammatory activity in vitro and in vivo.

Expression pattern of protease activated receptors in lymphoid cells.

Protease-activated receptors (PARs) are a subfamily of four G-protein-coupled receptors mediating multiple functions. PARs expression was studied in subpopulations of human lymphocytes. Our results indicate that natural killer cells expressed mRNA for PAR1, PAR2 and PAR3, CD4+ T cells expressed PAR1 and PAR2, while γδ and CD8+ T cells only expressed PAR1. PAR4 was absent at mRNA level and B cells did not express any PAR. Analyses of the cell surface PARs expression by flow cytometry were consistent with the mRNA data and also between different donors. PAR1 is the most abundant member of the PAR family present in lymphocytes.

Protease-activated receptor-2 signalling by tissue factor on dendritic cells suppresses antigen-specific CD4+ T-cell priming.

The precise function of tissue factor (TF) expressed by dendritic cells (DC) is uncertain. As well as initiating thrombin generation it can signal through protease-activated receptor 2 (PAR-2) when complexed with factor VIIa. We investigated the expression and function of TF on mouse bone marrow (BM) -derived DC; 20% of BM-derived DC expressed TF, which did not vary after incubation with lipopolysaccharide (LPS) or dexamethasone (DEX). However, the pro-coagulant activity of DEX-treated DC in recalcified plasma was 30-fold less than LPS-treated DC. In antigen-specific and allogeneic T-cell culture experiments, the TF on DEX-treated DC provided a signal through PAR-2, which contributed to the reduced ability of these cells to stimulate CD4(+) T-cell proliferation and cytokine production. In vivo, an inhibitory anti-TF antibody and a PAR-2 antagonist enhanced antigen-specific priming in two models where antigen was given without adjuvant, with an effect approximately 50% that seen with LPS, suggesting that a similar mechanism was operational physiologically. These data suggest a novel TF and PAR-2-dependent mechanism on DEX-DC in vitro and unprimed DC in vivo that contributes to the low immunogenicity of these cells. Targeting this pathway has the potential to influence antigen-specific CD4(+) T-cell activation.

Inhibition of neutrophil elastase attenuates airway hyperresponsiveness and inflammation in a mouse model of secondary allergen challenge: neutrophil elastase inhibition attenuates allergic airway responses.

BACKGROUND: Chronic asthma is often associated with neutrophilic infiltration in the airways. Neutrophils contain elastase, a potent secretagogue in the airways, nonetheless the role for neutrophil elastase as well as neutrophilic inflammation in allergen-induced airway responses is not well defined. In this study, we have investigated the impact of neutrophil elastase inhibition on the development of allergic airway inflammation and airway hyperresponsiveness (AHR) in previously sensitized and challenged mice. METHODS: BALB/c mice were sensitized and challenged (primary) with ovalbumin (OVA). Six weeks later, a single OVA aerosol (secondary challenge) was delivered and airway inflammation and airway responses were monitored 6 and 48 hrs later. An inhibitor of neutrophil elastase was administered prior to secondary challenge. RESULTS: Mice developed a two-phase airway inflammatory response after secondary allergen challenge, one neutrophilic at 6 hr and the other eosinophilic, at 48 hr. PAR-2 expression in the lung tissues was enhanced following secondary challenge, and that PAR-2 intracellular expression on peribronchial lymph node (PBLN) T cells was also increased following allergen challenge of sensitized mice. Inhibition of neutrophil elastase significantly attenuated AHR, goblet cell metaplasia, and inflammatory cell accumulation in the airways following secondary OVA challenge. Levels of IL-4, IL-5 and IL-13, and eotaxin in BAL fluid 6 hr after secondary allergen challenge were significantly suppressed by the treatment. At 48 hr, treatment with the neutrophil elastase inhibitor significantly reduced the levels of IL-13 and TGF-ß1 in the BAL fluid. In parallel, in vitro IL-13 production was significantly inhibited in spleen cells from sensitized mice. CONCLUSION: These data indicate that neutrophil elastase plays an important role in the development of allergic airway inflammation and hyperresponsiveness, and would suggest that the neutrophil elastase inhibitor reduced AHR to inhaled methacholine indicating the potential for its use as a modulator of the immune/inflammatory response in both the neutrophil- and eosinophil-dominant phases of the response to secondary allergen challenge.

Mucosal allergic sensitization to cockroach allergens is dependent on proteinase activity and proteinase-activated receptor-2 activation.

We have shown that proteinase-activated receptor-2 (PAR(2)) activation in the airways leads to allergic sensitization to concomitantly inhaled Ags, thus implicating PAR(2) in the pathogenesis of asthma. Many aeroallergens with proteinase activity activate PAR(2). To study the role of PAR(2) in allergic sensitization to aeroallergens, we developed a murine model of mucosal sensitization to cockroach proteins. We hypothesized that PAR(2) activation in the airways by natural allergens with serine proteinase activity plays an important role in allergic sensitization. Cockroach extract (CE) was administered to BALB/c mice intranasally on five consecutive days (sensitization phase) and a week later for four more days (challenge phase). Airway hyperresponsiveness (AHR) and allergic airway inflammation were assessed after the last challenge. To study the role of PAR(2), mice were exposed intranasally to a receptor-blocking anti-PAR(2) Ab before each administration of CE during the sensitization phase. Mucosal exposure to CE induced eosinophilic airway inflammation, AHR, and cockroach-specific IgG1. Heat-inactivated or soybean trypsin inhibitor-treated CE failed to induce these effects, indicating that proteinase activity plays an important role. The use of an anti-PAR(2) blocking Ab during the sensitization phase completely inhibited airway inflammation and also decreased AHR and the production of cockroach-specific IgG1. PAR(2) activation by CE acts as an adjuvant for allergic sensitization even in the absence of functional TLR4. We conclude that CE induces PAR(2)-dependent allergic airway sensitization in a mouse model of allergic airway inflammation. PAR(2) activation may be a general mechanism used by aeroallergens to induce allergic sensitization.

Protease-activated receptor 2-dependent fluid secretion from airway submucosal glands by house dust mite extract.

BACKGROUND: The submucosal gland (SMG) is important in the control of airway surface fluid. Protease-activated receptor (PAR) 2 contributes to the pathophysiology of allergies in response to nonspecific allergens bearing proteases and anion secretion. House dust mites (HDMs) have abundant proteases that can activate PAR2, but little is known about the direct effect of HDM on SMG secretion. OBJECTIVE: The aim of this study was to investigate the effect of HDMs on glandular secretion and its mechanism in allergic patients, patients with chronic rhinosinusitis (CRS), or both. METHODS: Inferior nasal turbinates were harvested from 55 patients and classified into 4 groups (the control, allergic rhinitis [AR], CRS, and AR+CRS groups). A microscope attached to a digital camera was used to quantify mucus bubbles from individual SMGs while stimulated with HDM extract, PAR2-activating peptide, and carbachol. PAR2 expression in the SMG was determined by means of immunostaining with anti-PAR2 mAb. RESULTS: HDM induced a significantly higher secretion rate and number of responding glands in the AR and AR+CRS groups than in the control group. Interestingly, patients in the CRS group, who had no HDM-specific IgE antibody, showed a higher response than the control group, and its response was suppressed by a PAR2-selective antagonist. The responses to PAR2-activating peptide were similar to those to HDM, and their secretion rates positively correlated with HDM responses. PAR2 was highly expressed in all 3 disease groups with immunostaining. CONCLUSIONS: HDM allergens can induce glandular secretion in patients with AR, CRS, or both, and PAR2 represents a possible mechanism for nonspecific hyperreactivity in inflammatory airway diseases.