We are investigating the role of cyclooxygenases in the pulmonary response to environmental agents. At baseline, lung prostaglandin E2 levels are lower in COX-1 null mice compared to either wild type or COX-2 null mice, but there are no significant differences in basal lung function or in lung histopathology between the genotypes. Following allergen (ovalbumin) sensitization/exposure, lung inflammatory indices are significantly greater in COX-1 null and COX-2 null mice compared to wild type mice. Airways of allergic COX-1 null mice have increased numbers of eosinophils and increased numbers of CD3+/CD4+ lymphocytes (Th cells). Alveolar macrophages from allergic COX-1 null airways show biochemical and morphologic evidence of activation. Bronchoalveolar lavage fluid (BALF) from allergic COX-1 null mice contains significantly higher levels of the Th2 cytokines IL-4, IL-5 and IL-13, increased levels of LTB4 and the cysteinyl leukotrienes, and increased levels of the chemokines TARC and eotaxin. These changes in the COX-1 null mice are associated with increased BALF IgE levels and increased MUC5AC production/mucin secretion. Moreover, expression of the adhesion molecules VCAM-1 and ICAM-1 are increased in the lungs of both allergic COX-1 and allergic COX-2 null mice. Allergic COX-1 null mice have reduced lung compliance, increased allergen-induced bronchoconstriction and display hyperresponsiveness to inhaled methacholine. We have also examined the effects of disruption of COX genes on the pulmonary responses to other environmentally relevant agents including inhaled endotoxin (bacterial lipopolysaccharide, LPS), vanadium pentoxide, and influenza virus. Following LPS exposure, all mice exhibit increased bronchoconstriction and methacholine hyperresponsiveness; however, these changes are much more pronounced in both the COX-1 null and COX-2 null mice relative to wild type controls. Interestingly, there are no significant differences in BALF cells or lung histopathology between the genotypes following LPS exposure. Thus, the balance of COX-1 and COX-2 is important in regulating the physiologic but not the inflammatory responses to inhaled LPS. Following vanadium pentoxide (V2O5) exposure, COX-2 null mice, but not COX-1 null mice, have increased acute lung inflammation and develop more lung fibrosis (increased lung hydroxyproline and enhanced trichrome staining). We have also utilized a pulmonary influenza infectivity model to evaluate host resistance and to determine if there are defects in innate or adaptive immune responses to viral infection in COX-1 null and COX-2 null mice. Mice were treated with a mouse adapted Hong Kong influenza A virus via the intranasal route and followed for 1 week to evaluate the innate immune response. We found that COX-2 null mice have an absent acute febrile response to viral infection, have reduced BALF cells, and have reduced levels of the proinflammatory cytokines TNFa, IL-1beta and interferon-gamma post-infection. Consistent with the attenuated innate immune response, viral titres are elevated in the lungs of COX-2 null mice vs. wild type mice post-infection. Moreover, spleen NK cell numbers and function are reduced in COX-2 null mice. In contrast, COX-1 null mice have increased BALF cells and increased levels of TNFa and IL-1beta post-infection. Thus, the response of COX-deficient mice varies depending on the environmental stimulus. We have recently developed transgenic mice with lung-specific overexpression of human COX-1 (murine CC10 promoter driven). These mice are being used to determine the effect of increased COX-derived eicosanoids on lung function at baseline and after various environmental stimuli.
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