PGI2 Controls Pulmonary NK Cells That Prevent Airway Sensitization to House Dust Mite Allergen.

In allergic asthma, inhalation of airborne allergens such as the house dust mite (HDM) effectively activates both innate and adaptive immunity in the lung mucosa. To determine the role of the eicosanoid PGI2 and its receptor IP during allergic airway sensitization, HDM responses in mice lacking a functional IP receptor (i.e., PGI2 IP receptor-deficient [IP-/-]) were compared with wild type (WT) mice. Surprisingly, IP-/- mice had increased numbers of pulmonary CD3-NK1.1+Ly49b+ NK cells producing IFN-γ that was inversely associated with the number of type 2 innate lymphoid cells (ILC2s) expressing IL-33Rα and IL-13 compared with WT animals. This phenomenon was associated with elevated CX3CL1 levels in the airways of IP-/- mice and treatment with a neutralizing Ab to CX3CL1 reduced IFN-γ production by the lung NK cells. Remarkably, IP-/- mice were less responsive to HDM challenge than WT counterparts because intranasal instillation of the allergen induced markedly reduced levels of airway eosinophils, CD4+ lymphocyte infiltration, and mucus production, as well as depressed levels of CCL2 chemokine and Th2 cytokines. NK cells were responsible for such attenuated responses because depletion of NK1.1+ cells in IP-/- mice restored both the HDM-induced lung inflammation and ILC2 numbers, whereas transfer of CD3-NK1.1+ NK cells into the airways of WT hosts suppressed the inflammatory response. Collectively, these data demonstrate a hitherto unknown role for PGI2 in regulating the number and properties of NK cells resident in lung tissue and reveal a role for NK cells in limiting lung tissue ILC2s and preventing allergic inflammatory responses to inhaled HDM allergen.

S-nitrosoglutathione reductase inhibition regulates allergen-induced lung inflammation and airway hyperreactivity.

Allergic asthma is characterized by Th2 type inflammation, leading to airway hyperresponsivenes, mucus hypersecretion and tissue remodeling. S-Nitrosoglutathione reductase (GSNOR) is an alcohol dehydrogenase involved in the regulation of intracellular levels of S-nitrosothiols. GSNOR activity has been shown to be elevated in human asthmatic lungs, resulting in diminished S-nitrosothiols and thus contributing to increased airway hyperreactivity. Using a mouse model of allergic airway inflammation, we report that intranasal administration of a new selective inhibitor of GSNOR, SPL-334, caused a marked reduction in airway hyperreactivity, allergen-specific T cells and eosinophil accumulation, and mucus production in the lungs in response to allergen inhalation. Moreover, SPL-334 treatment resulted in a significant decrease in the production of the Th2 cytokines IL-5 and IL-13 and the level of the chemokine CCL11 (eotaxin-1) in the airways. Collectively, these observations reveal that GSNOR inhibitors are effective not only in reducing airway hyperresponsiveness but also in limiting lung inflammatory responses mediated by CD4(+) Th2 cells. These findings suggest that the inhibition of GSNOR may provide a novel therapeutic approach for the treatment of allergic airway inflammation.

Prostaglandin I2promotes the development of IL-17-producing γδ T cells that associate with the epithelium during allergic lung inflammation.

γδ T cells rapidly produce cytokines and represent a first line of defense against microbes and other environmental insults at mucosal tissues and are thus thought to play a local immunoregulatory role. We show that allergic airway inflammation was associated with an increase in innate IL-17-producing γδ T (γδ-17) cells that expressed the αEß7 integrin and were closely associated with the airway epithelium. Importantly, PGI(2) and its receptor IP, which downregulated airway eosinophilic inflammation, promoted the emergence of these intraepithelial γδ-17 cells into the airways by enhancing IL-6 production by lung eosinophils and dendritic cells. Accordingly, a pronounced reduction of γδ-17 cells was observed in the thymus of naive mice lacking the PGI(2) receptor IP, as well as in the lungs during allergic inflammation, implying a critical role for PGI(2) in the programming of "natural" γδ-17 cells. Conversely, iloprost, a stable analog of PGI(2), augmented IL-17 production by γδ T cells but significantly reduced airway inflammation. Together, these findings suggest that PGI(2) plays a key immunoregulatory role by promoting the development of innate intraepithelial γδ-17 cells through an IL-6-dependent mechanism. By enhancing γδ-17 cell responses, stable analogs of PGI(2) may be exploited in the development of new immunotherapeutic approaches.

Design and evaluation of a novel fluorescent CB2 ligand as probe for receptor visualization in immune cells.

Cannabinoid CB2 receptor has emerged as a very promising target over the last decades. We have synthesized and evaluated a new fluorescent probe designated NMP6 based on 6-methoxyisatin scaffold, which exhibited selectivity and K(i) value at hCB2 of 387 nM. We have demonstrated its ability to be an effective probe for visualization of CB2 receptor binding using confocal microscopy and a flow cytometry probe for the analysis of CB2 protein expression. Furthermore, NMP6 was easily obtained in two chemical steps from commercially available building blocks.

Antigen-specific Treg regulate Th17-mediated lung neutrophilic inflammation, B-cell recruitment and polymeric IgA and IgM levels in the airways.

Th17 cells play key roles in mediating autoimmunity, inflammation and mucosal host defense against pathogens. To determine whether naturally occurring Treg (nTreg) limit Th17-mediated pulmonary inflammation, OVA-specific CD4+ Th17 cells and expanded CD4+CD25+Foxp3+ nTreg were cotransferred into BALB/c mice that were then exposed to OVA aerosols. Th17 cells, when transferred alone, accumulated in the lungs and posterior mediastinal LN and evoked a pronounced airway hyperreactivity and neutrophilic inflammation, characterized by B-cell recruitment and elevated IgA and IgM levels. Cotransfer of antigen-specific nTreg markedly reduced the Th17-induced pulmonary inflammation and associated neutrophilia, B-cell influx and polymeric Ig levels in the airways, but did not inhibit airway hyperreactivity. Moreover, the regulation appeared restricted to the site of mucosal inflammation, since transfer of nTreg did not affect the Th17 response developing in the lung draining LN, as evidenced by unaltered levels of IL-17 production and low numbers of Foxp3+ Treg. Our findings suggest a crucial role for Th17 cells in mediating airway B-cell influx and IgA response, and demonstrate that antigen-specific nTreg suppress Th17-mediated lung inflammation. These results provide new insights into how Th17 responses are limited and may facilitate development of novel approaches for controlling Th17-induced inflammation.

Cutting edge: lung mucosal Th17-mediated responses induce polymeric Ig receptor expression by the airway epithelium and elevate secretory IgA levels.

Polymeric Ig receptor (pIgR) is a central player in mucosal immunity that mediates the delivery of polymeric IgA and IgM to the apical surface of epithelial cells via transcytosis. Emerging evidence suggests that Th17 cells not only mediate autoimmunity but also play key roles in mucosal host defense against pathogens. We demonstrate that OVA-specific CD4(+) Th17 cells, in addition to causing neutrophilic inflammation in mice, mediated a pronounced influx of CD19(+) B cells into the lungs following Ag inhalation. Coincident with this recruitment was a striking induction in pIgR expression by the bronchial epithelium and a subsequent increase in airway IgM and secretory IgA levels. Intranasal administration of IL-17 revealed a crucial role for this cytokine in inducing pIgR expression by the epithelium. These findings support a key role for Th17 cells in pulmonary immune defense against respiratory pathogens by promoting pIgR-mediated transport of secretory IgA and IgM into the airway.

Prostaglandin I2-IP signaling blocks allergic pulmonary inflammation by preventing recruitment of CD4+ Th2 cells into the airways in a mouse model of asthma.

PGI(2) plays a key role in limiting Th2-mediated airway inflammation. In studies to investigate the mechanism underlying such regulation, we found that the PGI(2) receptor, IP, is preferentially expressed by effector CD4(+) Th2 cells, when compared with Th1 cells. Adoptive transfer of DO11.10 Th2 cells pretreated with PGI(2) resulted in considerably attenuated pulmonary inflammation and airway hyperreactivity in BALB/c recipient mice in response to OVA inhalation. This suppression was independent of increased cAMP levels, because pretreatment of Th2 cells with dibutyryl cAMP before transfer had no effect on airway inflammation. Moreover, PGI(2) pretreatment of Th2 cells suppressed the ability of the cells to infiltrate the lungs but not the spleen. In vitro studies showed that PGI(2) did not affect IL-4 and IL-5 production or the level of IFN-gamma by the T cells. However, the prostanoid strongly inhibited CCL17-induced chemotaxis of CD4(+) Th2 but not Th1 cells. The IP was implicated in this process since migration of wild-type Th2 cells in response to CCL17 was markedly reduced following treatment with PGI(2), whereas IP-deficient Th2 cells were unaffected and migrated effectively. Collectively, these experiments suggest that PGI(2), which is generated by endothelial cells during lung inflammatory response, serves to limit the influx of Th2 cells to the airways. Our results identify PGI(2)-IP as an important pathway for inhibiting allergic pulmonary inflammation by controlling recruitment of CD4(+) Th2 cells into the inflammatory site.