Immunologic aspects of surface infections in the lung.

The hallmark of cystic fibrosis is progressive bronchopulmonary damage associated with chronic infection with Pseudomonas aeruginosa, leading to respiratory failure and, ultimately, death. P. aeruginosa is an essentially nonvirulent organism in an immunocompetent host, but it has been shown to colonize the respiratory tract progressively in more than 80% of patients with CF. Patients with CF do not exhibit any evidence of immunologic compromise, and the infection is limited to the mucosal surfaces of the respiratory tract. Thus, P. aeruginosa in bronchopulmonary disease is a unique chronic mucosal infection resulting in a progressive pathologic process. It is therefore conceivable that locally induced alteration in the pulmonary mucosal defense is a major mechanism underlying the development of lung disease in patients with CF. An understanding of immunologic homeostasis in the mucous membranes and in the bronchopulmonary epithelium should provide a better perspective on the factors contributing to the acquisition and chronicity of P. aeruginosa infection in the lower respiratory tract and the development of progressive pulmonary damage unique to CF.