Bacterial infection and the pathogenesis of COPD.

Bacterial infection of the lower respiratory tract can impact on the etiology, pathogenesis, and the clinical course of COPD in several ways. Several recent cohort studies suggest that lung growth is impaired by childhood lower respiratory tract infection, making these individuals more vulnerable to developing COPD on exposure to additional injurious agents. Impairment of mucociliary clearance and local immune defense in smokers allows bacterial pathogens to gain a foothold in the lower respiratory tract. These pathogens and their products can cause further impairment of mucociliary clearance due to enhanced mucus secretion, disruption of normal ciliary activity, and airway epithelial injury, and thus persist in the lower respiratory tract. This chronic colonization of the lower respiratory tract by bacterial pathogens could induce a chronic inflammatory response with lung damage. Nontypeable Haemophilus influenzae, usually regarded as an extracellular mucosal pathogen, has been demonstrated to cause intracellular infections of the upper and lower respiratory tract respiratory tissue. Increased incidence of chronic Chlamydia pneumoniae infection of the respiratory tract has been associated with COPD. These chronic infections of respiratory tissues could contribute to the pathogenesis of COPD by altering the host response to cigarette smoke or by inducing a chronic inflammatory response. Application of newer molecular and immunologic research techniques is helping us define precisely the role of bacterial infection in COPD.