Asthma exacerbations due to exposures to air pollution and environmental allergens are common, leading to diminished responses to treatment and increased hospitalizations. Endotoxin or lipopolysaccharide (LPS) is a component of the cell wall of Gram- negative bacteria found throughout the environment. Individually, asthma and inhalation of LPS increases lung inflammation and airway hyperresponsiveness (AHR). Previous studies have shown that LPS exposure modulates both inflammatory and physiological responses in the lungs of asthmatic individuals. The primary focus of this work was to investigate the effects of inhaled LPS exposure on the pathology and physiological responses in the lung of a murine model of ovalbumin (OVA)<&ndash>-<&ndash> induced allergic asthma. Additionally, I investigated potential mechanisms that may underlie the dissociation between airway inflammation and AHR present in allergic mice exposed to LPS (OVA<&ndash>-<&ndash>LPS). I hypothesized that the attenuation of AHR in OVA-LPS mice was dependent on the upregulation of the gene responsible for nitric oxide production, Nos2, induced by the recruitment of neutrophils. Four specific aims were generated. In aim 1, I studied the relationships between the cellular character and distribution of lung lesions with components of AHR in OVA<&ndash>-<&ndash>LPS mice. To do so, naïve and OVA- induced allergic mice were exposed to LPS by intranasal instillation 48 hours following the final saline/OVA challenge. AHR was determined and animals were euthanized to collect tissue samples 24 hours after LPS exposure. There was significant pulmonary inflammation consisting of eosinophils distributed within the central airway compartment composed of perivascular and peribronchiolar regions (OVA group), neutrophils located in central airway and peripheral lung tissue compartments composed of alveolar septa and airspaces (LPS group), and OVA<&ndash>-<&ndash>LPS mice had more severe inflammation combining both cell types distributed in both compartments as well. AHR was increased in both central airways and the peripheral lung tissue in OVA and LPS mice. By comparison, AHR was attenuated in OVA<&ndash>-<&ndash>LPS mice. In aim 2, I hypothesized that recruited airway neutrophils contributed to the attenuation of AHR in OVA<&ndash>-<&ndash>LPS mice. Systemic depletion of neutrophils prior to LPS exposure significantly lowered BALF neutrophils. Compared to neutrophil sufficient mice, neutrophil depletion did not alter AHR in OVA<&ndash>-<&ndash>LPS mice. In aim 3, I hypothesized that LPS activation of the transcription factor, NF-κB, attenuated AHR in OVA<&ndash>-<&ndash>LPS mice. Following treatment with a novel NF-κB inhibitor, OVA<&ndash>-<&ndash>LPS mice had significantly decreased BALF macrophages, eosinophils, and lymphocytes but not neutrophils compared to non-treated mice. In spite of the decrease in cellularity, AHR significantly increased suggesting that NF-κB activation contributes to the attenuation of AHR in OVA<&ndash>-<&ndash>LPS mice. In aim 4, I evaluated the relationship between expression of the genes nitric oxide synthase-2 (Nos2) and arginase-1 (Arg1) and the attenuation of AHR in OVA<&ndash>-<&ndash>LPS mice. Following LPS exposure, Nos2 and Arg1were increased in OVA<&ndash>-<&ndash>LPS mice. Treatment with a NF-κB inhibitor significantly blunted the expression of both genes, suggesting that NF-κB mediated increased expression of Nos2 potentially contributes to attenuation in AHR, which is reversed with downregulation of Nos2 gene expression.
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