Predisposing conditions to bacterial infections in chronic obstructive pulmonary disease.

In normal airways, invasion of small numbers of pathogenic bacteria will not give rise to injury or local colonization. In chronic obstructive pulmonary disease, however, local conditions are changed, which may impair local defense systems and facilitate infection. These include: (1) factors promoting bacterial adherence and growth like the observed damaged airway epithelium in chronic bronchitis. The consequent changes in the composition of the epithelial lining fluid and impaired mucociliary clearance may be the most important pathophysiologic airway sequele in this respect; (2) aggravating generalized airway obstruction including mucus secretion, increase in mucus viscosity, and proliferation of submucosal smooth muscles, resulting in significant changes in airway geometry. This may change local conditions dramatically and so sustain factors promoting bacterial infections; (3) subversion of normally protective defense mechanisms into damaging host tissue at the mucosal level. Activated epithelial cell layers induce increased submucosal vascular leakage, edema, and inflammatory cell infiltration with subsequent tissue injury by locally produced cell products like free elastase. Specific bacterial products but also generally produced bacterial endotoxins may induce a local immune response resulting in the local production of high concentrations of antibodies and an invasion of specific effector cells. The role of these reactive cells or proteins may even be a primary one, in that they attack on (cellular) proteins, which increase their susceptibility for dysfunction in the defense line. For the clinicians, the new insights in the role of these aggravating factors in the development of recurrent bacterial airway infections in chronic bronchitis may be of major importance.(ABSTRACT TRUNCATED AT 250 WORDS)