Kevan Roberts

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.

CD4+CD25+ T Cells Regulate Airway Eosinophilic Inflammation by Modulating the Th2 Cell Phenotype

We used a TCR-transgenic mouse to investigate whether Th2-mediated airway inflammation is influenced by Ag-specific CD4+CD25+ regulatory T cells. CD4+CD25+ T cells from DO11.10 mice expressed the transgenic TCR and mediated regulatory activity. Unexpectedly, depletion of CD4+CD25+ T cells before Th2 differentiation markedly reduced the expression of IL-4, IL-5, and IL-13 mRNA and protein when compared with unfractionated (total) CD4+ Th2 cells. The CD4+CD25−-derived Th2 cells also expressed decreased levels of IL-10 but were clearly Th2 polarized since they did not produce any IFN-γ. Paradoxically, adoptive transfer of CD4+CD25−-derived Th2 cells into BALB/c mice induced an elevated airway eosinophilic inflammation in response to OVA inhalation compared with recipients of total CD4+ Th2 cells. The pronounced eosinophilia was associated with reduced levels of IL-10 and increased amounts of eotaxin in the bronchoalveolar lavage fluid. This Th2 phenotype characterized by reduced Th2 cytokine expression appeared to remain stable in vivo, even after repeated exposure of the animals to OVA aerosols. Our results demonstrate that the immunoregulatory properties of CD4+CD25+ T cells do extend to Th2 responses. Specifically, CD4+CD25+ T cells play a key role in modulating Th2-mediated pulmonary inflammation by suppressing the development of a Th2 phenotype that is highly effective in vivo at promoting airway eosinophilia. Conceivably, this is partly a consequence of regulatory T cells facilitating the production of IL-10.

A Key Role for Prostaglandin I2 in Limiting Lung Mucosal Th2, But Not Th1, Responses to Inhaled Allergen

The cellular events that serve to regulate lung mucosal Th2 responses and limit allergic inflammatory reactions are unclear. Using the DO11.10 TCR transgenic mouse, we developed a model of T cell-mediated pulmonary inflammation and demonstrated that high levels of PGI2 are produced in the airways following OVA inhalation. Selective inhibition of cyclooxygenase-2 in vivo specifically reduced PGI2 synthesis and resulted in a marked increase in Th2-mediated, but not Th1-mediated, lung inflammation. The elevated Th2-mediated inflammatory response elicited by the cyclooxygenase-2 inhibitor was associated with enhanced airway hyperreactivity and was coincident with a marked increase in the levels of IL-4, IL-5, and IL-13 in the airways, but a reduction in IL-10 production. In keeping with these observations, we found that the mRNA for the PGI2 receptor was expressed by Th2, but not Th1, cells, and transcripts for the PGI2 receptor were induced by IL-4 and OVA peptide stimulation. Interestingly, treatment with PGI2 or its stable analog, carbaprostacyclin, augmented IL-10 production by Th2 cells. Collectively, our findings reveal a key role for PGI2 in differentially limiting Th2 responses, possibly by promoting production of the immunosuppressive cytokine IL-10 at the site of allergic lung inflammation. These results indicate an important role for prostanoids generated during inflammation in regulating mucosal T cell responses and highlight a potential risk in the use of cyclooxygenase-2-specific inhibitors by allergic asthmatics.

Prostaglandin I2-IP Signaling Blocks Allergic Pulmonary Inflammation by Preventing Recruitment of CD4+ Th2 Cells into the Airways in a Mouse Model of Asthma

PGI2 plays a key role in limiting Th2-mediated airway inflammation. In studies to investigate the mechanism underlying such regulation, we found that the PGI2 receptor, IP, is preferentially expressed by effector CD4+ Th2 cells, when compared with Th1 cells. Adoptive transfer of DO11.10 Th2 cells pretreated with PGI2 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, PGI2 pretreatment of Th2 cells suppressed the ability of the cells to infiltrate the lungs but not the spleen. In vitro studies showed that PGI2 did not affect IL-4 and IL-5 production or the level of IFN-γ 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 PGI2, whereas IP-deficient Th2 cells were unaffected and migrated effectively. Collectively, these experiments suggest that PGI2, which is generated by endothelial cells during lung inflammatory response, serves to limit the influx of Th2 cells to the airways. Our results identify PGI2-IP as an important pathway for inhibiting allergic pulmonary inflammation by controlling recruitment of CD4+ Th2 cells into the inflammatory site.

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.

Cultured nasal polyps from nonatopic and atopic patients release RANTES spontaneously and after stimulation with phytohemagglutinin

BACKGROUND Eosinophil infiltration of tissue is a hallmark of nasal polyposis in both nonatopic and atopic patients. These cells are thought to play a key role in the nasal polyp inflammatory process. OBJECTIVE The objective of this study was to investigate whether cultured nasal polyps derived from nonatopic and atopic patients release RANTES both spontaneously and after phytohemagglutinin (PHA) stimulation. METHODS Nasal polyps were obtained from 12 subjects (6 nonatopic and 6 atopic), cut into 2 to 3 mm large specimens, and cultured for 48 hours with or without PHA. RANTES was measured in the culture supernatant by ELISA (R&D Systems, U.K.). RESULTS Immunoreactive RANTES was found to be present in the culture supernatant of nasal polyps derived from both nonatopic and atopic patients with no difference between the two groups (median: 3.8 vs 2.9 pg/mg/ml). On incubation with PHA, nasal polyps from both nonatopic and atopic patients released sevenfold and 11-fold greater amounts of RANTES than unstimulated samples. As determined by immunohistochemistry, RANTES was localized to the vascular endothelium in nasal polyps from both groups of patients. CONCLUSIONS This study demonstrates that cultured nasal polyps derived from both nonatopic and atopic patients release RANTES spontaneously and after PHA stimulation. This observation and the finding that RANTES is present in nasal polyp endothelial cells suggest that this chemokine may be an important mediator of eosinophil and lymphocyte recruitment in both nonatopic and atopic nasal polyposis.

Natural Foxp3+ regulatory T cells inhibit Th2 polarization but are biased toward suppression of Th17-driven lung inflammation

nTregs prevent autoimmunity and modulate immune and inflammatory responses to foreign antigens. CD4+Foxp3+ nTregs from DO11.10 mice were expanded ex vivo, and their effectiveness in suppressing the development of lung inflammatory responses, elicited by differentiated CD4+ T cells following antigen inhalation, was examined. Effector DO11.10 CD4+ Th2 cells, when adoptively transferred into BALB/c mice that subsequently inhaled OVA, elicited a pronounced pulmonary, eosinophilic inflammation. Surprisingly, the cotransfer of expanded nTregs failed to suppress the Th2‐mediated airway inflammation. Nevertheless, expanded OVA‐specific CD4+Foxp3+ nTregs were highly effective at inhibiting the polarization of naïve CD4+ T cells into a Th2 phenotype. This suppression was reversed by an antibody to GITR but was not affected by the presence of the soluble OX40L. Further analysis revealed that although nTregs also failed to inhibit the lung neutrophilic inflammation induced by effector CD4+ Th1 cells, they markedly suppressed pulmonary inflammation elicited by CD4+ Th17 cells but not AHR. The suppression of the Th17‐mediated response was evident from a striking reduction in the proportion of OVA‐specific T cells expressing IL‐17 and the numbers of neutrophils present in the airways of Th17 recipient mice. Collectively, these results demonstrate that expanded nTregs clearly limit the Th2 polarization process and that Th17‐mediated inflammatory responses are particularly prone to the immunoregulatory properties of nTregs. These findings thus indicate that expanded nTregs are restrictive in their ability to suppress airway inflammatory processes and AHR.

Allergen-induced release of GM-CSF and IL-8 in vitro by nasal polyp tissue from atopic subjects prolongs eosinophil survival

Eosinophilia is a feature of nasal polyposis. The aim of this study was to determine the role of cytokines and allergen in maintaining the eosinophilic infiltrate in this condition. Polyp fragments from house dust mite (HDM)-sensitive atopic individuals and nonatopic individuals were cultured in the presence of HDM, or phytohaemagglutinin (PHA) or culture medium alone. Culture supernatants were assayed for interleukins (IL) 3, 5, and 8 and granulocyte macrophage colony stimulating factor (GM-CSF), and eosinophil survival enhancing activity (ESEA) in vitro. Significant ESEA was produced spontaneously. When polyp tissue from atopics, but not from nonatopics, was stimulated with allergen for 2 days there was a further increase in ESEA associated with a median 12 and fourfold increase in IL-8 and GM-CSF, respectively. This increased ESEA was markedly reduced with anti-GM-CSF and, to a lesser extent, anti-IL-8 blocking antibodies. When stimulated with PHA, polyp tissue from atopic subjects also produced increased ESEA, implicating possible T-cell involvement. This was associated with a small (twofold), but significant, increase in IL-8 and a less consistent increase in GM-CSF. However, anti-IL-8 or anti-GM-CSF blocking antibodies failed to reduce the ESEA in these supernatants, suggesting involvement of other mechanisms. This study suggests that in sensitized individuals, allergen may contribute to polyp eosinophilia by stimulating the production of granulocyte/macrophage colony stimulating factor and interleukin 8.

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 I2 Promotes 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 αEβ7 integrin and were closely associated with the airway epithelium. Importantly, PGI2 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 PGI2 receptor IP, as well as in the lungs during allergic inflammation, implying a critical role for PGI2 in the programming of “natural” γδ-17 cells. Conversely, iloprost, a stable analog of PGI2, augmented IL-17 production by γδ T cells but significantly reduced airway inflammation. Together, these findings suggest that PGI2 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 PGI2 may be exploited in the development of new immunotherapeutic approaches.