Airway epithelial NF-κB activation promotes the ability to overcome inhalational antigen tolerance.

BACKGROUND: Inhalational antigen tolerance typically protects against the development of allergic airway disease but may be overcome to induce allergic sensitization preceding the development of asthma. OBJECTIVES: We examined in vivo whether pre-existing inhalational antigen tolerance could be overcome by activation of the transcription factor NF-κB in conducting airway epithelial cells, and used a combination of in vivo and in vitro approaches to examine the mechanisms involved. METHODS: Wild-type and transgenic mice capable of expressing constitutively active IκB kinase ß (CAIKKß) in airway epithelium were tolerized to inhaled ovalbumin. Twenty-eight days later, the transgene was transiently expressed and mice were exposed to inhaled OVA on Day 30 in an attempt to overcome inhalational tolerance. RESULTS: Following ovalbumin challenge on days 40-42, CAIKKß mice in which the transgene had been activated exhibited characteristic features of allergic airway disease, including airway eosinophilia and methacholine hyper-responsiveness. Increases in the CD103(+) and CD11b(HI) lung dendritic cell populations were present in CAIKKß mice on Day 31. Bronchoalveolar lavage from mice expressing CAIKKß mice induced CD4(+) T cells to secrete T(H)2 and T(H)17 cytokines, an effect that required IL-4 and IL-1 signalling, respectively. CAIKKß mice on Dox demonstrated increased numbers of innate lymphoid type 2 cells (ILC2) in the lung, which also exhibited elevated mRNA expression of the T(H)2-polarizing cytokine IL-4. Finally, airway epithelial NF-kB activation induced allergic sensitization in CAIKKß mice on Dox that required IL-4 and IL-1 signalling in vivo. CONCLUSIONS: Our studies demonstrate that soluble mediators generated in response to airway epithelial NF-κB activation orchestrate the breaking of inhalational tolerance and allergic antigen sensitization through the effects of soluble mediators, including IL-1 and IL-4, on pulmonary dendritic cells as well as innate lymphoid and CD4(+) T cells.

Essential role of IL-6 in protection against H1N1 influenza virus by promoting neutrophil survival in the lung.

Influenza virus infection is considered a major worldwide public health problem. Seasonal infections with the most common influenza virus strains (e.g., H1N1) can usually be resolved, but they still cause a high rate of mortality. The factors that influence the outcome of the infection remain unclear. Here, we show that deficiency of interleukin (IL)-6 or IL-6 receptor is sufficient for normally sublethal doses of H1N1 influenza A virus to cause death in mice. IL-6 is necessary for resolution of influenza infection by protecting neutrophils from virus-induced death in the lung and by promoting neutrophil-mediated viral clearance. Loss of IL-6 results in persistence of the influenza virus in the lung leading to pronounced lung damage and, ultimately, death. Thus, we demonstrate that IL-6 is a vital innate immune cytokine in providing protection against influenza A infection. Genetic or environmental factors that impair IL-6 production or signaling could increase mortality to influenza virus infection.

Interferon-gamma for delayed pulmonary toxicity syndrome resistant to steroids.

Delayed pulmonary toxicity syndrome, characterized by interstitial pneumonia and pulmonary fibrosis, is common following high-dose bischloroethylnitrosourea (BCNU) (carmustine, [1,3-bis (2-chloroethyl)-1-nitrosourea]) containing chemotherapeutic regimens. Depending upon the treatment protocol, it may develop in over 70% of patients. Early and aggressive corticosteroid treatment leads to improvement in the majority of patients. However, up to 8% of affected patients may fail to respond to corticosteroids and develop progressive respiratory failure leading to death. No alternatives to corticosteroids have thus far been shown useful. We report the symptomatic and physiological improvement of a patient with severe steroid-resistant delayed pulmonary toxicity syndrome, following treatment with interferon-gamma.

Neutrophil maturation and activation determine anatomic site of clearance from circulation.

The long-term disposition of circulating neutrophils and the site of disappearance from circulation remain unclear. We investigated neutrophil localization in mice using (111)In-labeled murine peripheral blood neutrophils, mature bone marrow neutrophils, and peritoneal exudate neutrophils to track in vivo localization of these different cell populations. Infused peripheral neutrophils were found to localize equally between liver and marrow sites by 4 h (31.2 +/- 1.9 vs. 31.9 +/- 1.8%), whereas exudate neutrophils predominantly localized to liver (42.0 +/- 1.1%) and marrow-derived neutrophils to the marrow (65.9 +/- 6.6%) where they were found to localize predominantly in the hematopoietic cords. Stimulation of marrow neutrophils before infusion caused a shift in localization from marrow to liver, and subsequent induction of an inflammatory site after infusion and marrow sequestration led to remobilization of infused marrow neutrophils but not of peripheral neutrophils. These results indicate that the marrow participates in removing neutrophils from circulation, with evidence supporting both storage and perhaps disposal functions. Furthermore, models for circulating neutrophil homeostasis should consider that the site of retention is governed by the maturation and activation states of the cell.

Role of p38 mitogen-activated protein kinase in a murine model of pulmonary inflammation.

Early inflammatory events include cytokine release, activation, and rapid accumulation of neutrophils, with subsequent recruitment of mononuclear cells. The p38 mitogen-activated protein kinase (MAPK) intracellular signaling pathway plays a central role in regulating a wide range of inflammatory responses in many different cells. A murine model of mild LPS-induced lung inflammation was developed to investigate the role of the p38 MAPK pathway in the initiation of pulmonary inflammation. A novel p38 MAPK inhibitor, M39, was used to determine the functional consequences of p38 MAPK activation. In vitro exposure to M39 inhibited p38 MAPK activity in LPS-stimulated murine and human neutrophils and macrophages, blocked TNF-alpha and macrophage inflammatory protein-2 (MIP-2) release, and eliminated migration of murine neutrophils toward the chemokines MIP-2 and KC. In contrast, alveolar macrophages required a 1000-fold greater concentration of M39 to block release of TNF-alpha and MIP-2. Systemic inhibition of p38 MAPK resulted in significant decreases in the release of TNF-alpha and neutrophil accumulation in the airspaces following intratracheal administration of LPS. Recovery of MIP-2 and KC from the airspaces was not affected by inhibition of p38 MAPK, and accumulation of mononuclear cells was not significantly reduced. When KC was instilled as a proinflammatory stimulus, neutrophil accumulation was significantly decreased by p38 MAPK inhibition independent of TNF-alpha or LPS. Together, these results demonstrate a much greater dependence on the p38 MAPK cascade in the neutrophil when compared with other leukocytes, and suggest a means of selectively studying and potentially modulating early inflammation in the lung.