Ryan J. Norton

Extravascular fibrin, plasminogen activator, plasminogen activator inhibitors, and airway hyperresponsiveness

Mechanisms underlying airway hyperresponsiveness are not yet fully elucidated. One of the manifestations of airway inflammation is leakage of diverse plasma proteins into the airway lumen. They include fibrinogen and thrombin. Thrombin cleaves fibrinogen to form fibrin, a major component of thrombi. Fibrin inactivates surfactant. Surfactant on the airway surface maintains airway patency by lowering surface tension. In this study, immunohistochemically detected fibrin was seen along the luminal surface of distal airways in a patient who died of status asthmaticus and in mice with induced allergic airway inflammation. In addition, we observed altered airway fibrinolytic system protein balance consistent with promotion of fibrin deposition in mice with allergic airway inflammation. The airways of mice were exposed to aerosolized fibrinogen, thrombin, or to fibrinogen followed by thrombin. Only fibrinogen followed by thrombin resulted in airway hyperresponsiveness compared with controls. An aerosolized fibrinolytic agent, tissue-type plasminogen activator, significantly diminished airway hyperresponsiveness in mice with allergic airway inflammation. These results are consistent with the hypothesis that leakage of fibrinogen and thrombin and their accumulation on the airway surface can contribute to the pathogenesis of airway hyperresponsiveness.

Inhibition of Arginase Activity Enhances Inflammation in Mice with Allergic Airway Disease, in Association with Increases in Protein S-Nitrosylation and Tyrosine Nitration

Pulmonary inflammation in asthma is orchestrated by the activity of NF-κB. NO and NO synthase (NOS) activity are important modulators of inflammation. The availability of the NOS substrate, l-arginine, is one of the mechanisms that controls the activity of NOS. Arginase also uses l-arginine as its substrate, and arginase-1 expression is highly induced in a murine model of asthma. Because we have previously described that arginase affects NOx content and interferes with the activation of NF-κB in lung epithelial cells, the goal of this study was to investigate the impact of arginase inhibition on the bioavailability of NO and the implications for NF-κB activation and inflammation in a mouse model of allergic airway disease. Administration of the arginase inhibitor BEC (S-(2-boronoethyl)-l-cysteine) decreased arginase activity and caused alterations in NO homeostasis, which were reflected by increases in S-nitrosylated and nitrated proteins in the lungs from inflamed mice. In contrast to our expectations, BEC enhanced perivascular and peribronchiolar lung inflammation, mucus metaplasia, NF-κB DNA binding, and mRNA expression of the NF-κB-driven chemokine genes CCL20 and KC, and lead to further increases in airways hyperresponsiveness. These results suggest that inhibition of arginase activity enhanced a variety of parameters relevant to allergic airways disease, possibly by altering NO homeostasis.

Inhibition of NFAT specifically in T cells prevents allergic pulmonary inflammation.

NFAT is a family of transcription factors important in the regulation of cytokine genes and is widely expressed in different lymphoid and nonlymphoid tissues. Consequently, the role of NFAT in CD4+ T cells during an in vivo immune response is not completely clear. In this study, we use transgenic mice expressing a dominant negative NFAT mutant exclusively in T cells to address the role of NFAT in T cells during a Th2 immune response in a model of allergic airway inflammation. We have observed that inhibition of NFAT in T cells results in a reduction of Ag-specific Th2 Ab levels and IL-4 production by CD4+ T cells. The accumulation of eosinophils in the bronchoalveolar lavage is delayed in dominant negative NFAT-transgenic mice. These mice are also more resistant to the development of lung pathology in response to allergen exposure. We, therefore, conclude that activation of NFAT in CD4+ T cells is required for the development of a Th2 immune response in vivo and allergic airway inflammation.