Genetics of Asthma - Bronchoscopy Studies

Overview

The purpose of this study is to identify the mediators and genes in airway epithelial and BAL cells that are differentially regulated following inhalation of endotoxin lipopolysaccharide (LPS) among study participants with allergic asthma and normal phenotypes. This approach is designed to identify novel genes associated with both asthma pathogenesis and asthma susceptibility. LPS, or endotoxin, a cell wall component of gram-negative bacteria, is ubiquitous in the environment, and is thought to influence both susceptibility and severity of asthma. 240 subjects (healthy adult men and women (age \>18-40) with and without atopy and asthma) will complete the screening evaluations in order to establish 3 study groups of 60 subjects each. Each qualified subject will undergo an inhaled LPS endotoxin challenge followed by bronchoscopy after 24 hours, which will consist of a bronchoalveolar lavage (BAL) and endobronchial brush biopsies. BAL involves squirting a small amount of sterile salt water into one of the airways then gently taking it back out through the bronchoscope. The brush sample involves gently moving a small brush back and forth in an airway to collect cell samples. Samples of whole blood will also be obtained at various time points. RNA will be isolated from these cell populations in order to assess differential gene expression expression using microarrays.

Background: Endotoxin or lipopolysaccharide (LPS), a cell wall component of gram-negative bacteria, is ubiquitous in the environment, and is often present in high concentrations in organic dusts, as well as in air pollution, and household dusts. There is convincing evidence that endotoxin exacerbates airflow obstruction and airway inflammation in allergic asthmatics. Additional findings indicate that allergic airways can enhance the response to inhaled endotoxin, and that endotoxin can enhance the airway response to allergens. However, when considering the interaction between endotoxin and allergens, the timing of the exposure appears to be critical. Emerging evidence suggests that early exposure to endotoxin, a potent inducer of Th1 type cytokines (IFN-g and IL-12), may minimize the risk of allergen sensitization which could has profound effects on reducing the risk of developing asthma in children. Independent of its effect in allergic asthma, several studies demonstrate that inhalation of air contaminated with endotoxin is associated with the classical features of asthma (reversible airflow obstruction and airway inflammation, and persistent airway hyperreactivity and airway remodeling). Epidemiological studies have shown that the concentration of inhaled endotoxin in the bioaerosol is strongly and consistently associated with reversible airflow obstruction among cotton workers, agricultural workers, and fiberglass workers. Importantly, the concentration of endotoxin in the bioaerosol is the most important occupational exposure associated with the development and progression of airway disease in agricultural workers. Experimentally, inhalation of endotoxin can cause reversible airflow obstruction and airway inflammation in previously unexposed healthy study subjects. The ability of the host to respond to endotoxin is highly variable, and is influenced in part by genetic factors.: The rationale for this investigation is based on the following points: * asthma is caused in large part by both genetic susceptibility and environmental exposure, * a variety of immune and non-immune mechanisms can function independently or interactively to cause airway hyper-reactivity, airflow obstruction, airway inflammation, and airway remodeling, * environmental challenges can be used to "narrow the asthma phenotype" and allow one to investigate unique gene-environment interactions that are involved in the development of biologically specific forms of asthma, * genes that are over or under stimulated in the airway epithelia of asthmatics following inhalation challenge are important in the pathogenesis of asthma