Trypsin and mast cell tryptase can signal to epithelial cells, myocytes, and nerve fibers of the respiratory tract by cleaving proteinase-activated receptor 2 (PAR2). Since tryptase inhibitors are under development to treat asthma, a precise understanding of the contribution of PAR2 to airway inflammation is required. We examined the role of PAR2 in allergic inflammation of the airway by comparing OVA-sensitized and -challenged mice lacking or overexpressing PAR2. In wild-type mice, immunoreactive PAR2 was detected in airway epithelial cells and myocytes, and intranasal administration of a PAR2 agonist stimulated macrophage infiltration into bronchoalveolar lavage fluid. OVA challenge of immunized wild-type mice stimulated infiltration of leukocytes into bronchoalveolar lavage and induced airway hyperreactivity to inhaled methacholine. Compared with wild-type animals, eosinophil infiltration was inhibited by 73% in mice lacking PAR2 and increased by 88% in mice overexpressing PAR2. Similarly, compared with wild-type animals, airway hyperreactivity to inhaled methacholine (40 μg/ml) was diminished 38% in mice lacking PAR2 and increased by 52% in mice overexpressing PAR2. PAR2 deletion also reduced IgE levels to OVA sensitization by 4-fold compared with those of wild-type animals. Thus, PAR2 contributes to the development of immunity and to allergic inflammation of the airway. Our results support the proposal that tryptase inhibitors and PAR2 antagonists may be useful therapies for inflammatory airway disease.

CD4(+) T cells are thought to play a major role in the initiation and perpetuation of T helper cell, type 2 (Th2)-like allergic airway inflammation. However, it is not clear whether activation of resident antigen-specific CD4(+) T cells is in itself sufficient to induce such a phenotype. Using ovalbumin (OVA)-specific alphabeta-T cell receptor transgenic Balb/c DO11.10 mice, we were able to test this hypothesis. Nonsensitized DO11.10 mice but not wild-type mice responded to a primary OVA aerosol with a rapid and impressive bronchoalveolar lavage (BAL) neutrophilia followed by a smaller but significant eosinophilia. Responses in DO11.10 mice were mediated by OVA-specific activation of CD4(+) T cells because in vivo depletion of CD4(+) but not CD8(+) T cells abrogated inflammatory cell influx. Cytokines measured in BAL fluid (BALF) after OVA aerosol exposure of DO11.10 mice were indicative of a T helper cell, type 1 (Th1)-like immune response. Further, neutralization of interferon gamma (IFN-gamma) with antibody enhanced eosinophil influx, suggesting that IFN-gamma production was limiting the development of a Th2 response. Despite this, an increased prevalence of cells staining for mucus was seen in the bronchial epithelium, a feature more commonly associated with a Th2-immune response. Unlike what was seen in OVA-sensitized wild-type mice, multiple OVA aerosol exposures of DO11.10 mice failed to induce airway hyperresponsiveness (AHR) to inhaled methacholine. In conclusion, in vivo stimulation of resident lung CD4(+) T cells with antigen caused lung inflammation with characteristics of both a Th1- and Th2-immune response but was insufficient to directly induce AHR.

1 The neuromuscular blocking agents tubocurarine, atracurium and pancuronium have been tested for their ability to inhibit receptor-mediated increases in the K+ permeability of intestinal smooth muscle. 2 All three agents, as well as the bee venom peptide apamin, reduced both the resting efflux of 86Rb and the increase in efflux caused by the application of either bradykinin (1 jM) or an a,-adrenoceptor agonist, amidephrine (20 giM), to depolarized strips of guinea-pig taenia caeci. This suggested that, like apamin, the neuromuscular blocking agents inhibit the Ca2+-dependent K' permeability (PK(Ca)) mechanism which in this tissue is activated by a variety of membrane receptors.3 The concentrations (IC50s) of atracurium, pancuronium and (+ )-tubocurarine which reduced the effect of amidephrine on 86Rb efflux by 50% were 12, 37 and 67 jM respectively. 4 Also in keeping with an ability to block PK(Ca), the neuromuscular blockers and apamin reduced the inhibition by amidephrine and bradykinin of physalaemin-mediated contractions of the taenia caeci.The IC50 values were 15, 31 and 120 jiM for atracurium, tubocurarine and pancuronium respectively, and 2.3 nM for apamin. 5 Each of the neuromuscular blockers, and apamin, increased the spontaneous contractions of the rabbit duodenum and blocked the inhibitory effect of amidephrine thereon.6 It is concluded that the PK(Ca) mechanism in the longitudinal smooth muscle of the intestine resembles that of hepatocytes and sympathetic ganglion cells in its susceptibility to inhibition by neuromuscular blocking agents, as well as by apamin.

Ag-specific activation of CD4+ T cells is known to be causative for the cytokine production associated with lung allergy. Chemokine-induced leukocyte recruitment potentially represents a critical early event in Ag-induced lung inflammation. Whether Ag-specific, lung CD4+ T cell activation is important in lung chemokine production is currently not clear. Using αβ-TCR transgenic BALB/c DO11.10 mice, we investigated the ability of Ag-specific CD4+ T cell activation to induce lung chemokine production and leukocyte recruitment. Within 1 h of exposure of DO11.10 mice to OVA aerosol, lung mRNA and protein for the neutrophil chemokines KC and macrophage inflammatory protein (MIP)-2 were greatly increased. Accordingly, neutrophils in the airways increased by >50-fold, and KC and MIP-2 proved to be functional because their neutralization significantly reduced airway neutrophilia. CD4+ T cell activation was critical because CD4+ but not CD8+ T cell depletion reduced KC production, which correlated well with the previously observed inhibition of neutrophil influx after CD4+ T cell depletion. In vitro studies confirmed that OVA-induced KC and MIP-2 production was conditional upon the interaction of CD4+ T cells with APCs. A likely secondary mediator was TNF-α, and a probable source of these chemokines in the lung was alveolar macrophages. Thus, Ag-specific CD4+ T cell activation in the lung leads to rapid up-regulation of neutrophil chemokines and the recruitment of neutrophils to the site of Ag exposure. This may be a key early event in the pathogenesis of Ag-induced lung inflammation.

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