Functional Implications of TNF

Exposure of the airways to air toxins initiates transient and reversible airway injury to both adults and young children. Repetitive exposures of children residing within high oxidant communities leads to impairment of lung growth and pulmonary function, and remodeling of airway epithelial tissues is also suggested to occur. In the completely normal/healthy airway, exposure to ozone (O3), a ubiquitous urban air pollutant, induces an inflammatory response that is characterized by increases in epithelial permeability, neutrophilic infiltration, and bronchial hyperreactivity. Inhalation by humans of the pleiotropic pro-inflammatory cytokine tumor necrosis factor (Tnf) leads to the development of nearly identical responses: hyperresponsiveness of the bronchial airway (AHR), and neutrophil influx. Using controlled exposure to O3 in a laboratory setting, we have recently established a link between a genetic single nucleotide polymorphism (SNP) of TNF gene (-308) and the development of AHR to methacholine within a 24 h time frame, post exposure to O3. In a healthy human study group (n=137) the presence of a common TNF (-308) SNP was found to confer susceptibility to an ambient concentration of O3 (220 ppb, and frequently attained in many cities of the US during the summer months): stratified for ethnicity, Caucasian subjects who were homozygotic (A/A) or heterozygotic (G/A) for the minor allele of the TNF (-308) SNP were 2-times as likely to develop sensitivity to methacholine after O3 as compared to subjects with the wild-type, major allele (G/G) haplotype.

Literature reports suggest that the TNF(-308) polymorphism associates with increased TNF gene transcription and increased Tnf cytokine production. However, the functional significance of this common TNF polymorphism remains uncertain; and moreover, the functional implications of the TNF(-308) polymorphism in the lung remain undeveloped. We hypothesize that subjects either homozygotic (A/A) or heterozygotic (G/A) for the minor allele of the TNF(-308) promoter polymorphism, will demonstrate enhancement in phenotypic responses to O3 including: increased cellular inflammation and secretion of pre-inflammation cytokines, enhanced activation of resident alveolar macrophages, and altered bronchial sensitivity, leading to AHR.

Our research plan is designed to mechanistically investigate the interaction between host factors of humans and exposure to the prototypal air pollutant, ozone. The research plan will expand upon, and enable, a clear assignment of the functional contribution of a common SNP of TNF gene to the initiation of airway hyperresponsiveness, a cardinal feature of inflammatory airway disease.