Microbial-host interactions in the airways in chronic respiratory infection.

The pathogenic events that take place in chronic respiratory infection highlight the successful microbial strategy of survival by persistence, or colonization. Microorganisms implement their strategy of persistence by two principal tactics: (1) sabotage of the host's bronchial defenses (ie, direct microbe-mediated damage to the host), and (2) subversion of the host's normally protective defenses into damaging host tissue itself (ie, indirect host-mediated damage provoked by the microbe). Among the various ways in which microorganisms directly damage host defenses and facilitate their own persistence in the respiratory tract are inhibition of ciliary function, inhibition of mucociliary transport, alteration of ion transport in respiratory epithelium, stimulation of mucus production, and damage to respiratory epithelium. Patients with chronic respiratory infection suffer a vicious circle of events leading to progressive lung damage and cardio-respiratory failure. Treatments to break this circle include antimicrobial therapy to reduce microbial colonization and anti-inflammatory/immunosuppressive therapy to modulate damaging host responses.