Immunohistopathologic Localization ofPseudomonas aeruginosain Lungs from Patients with Cystic Fibrosis: Implications for the Pathogenesis of Progressive Lung Deterioration

Abstract

Despite studies of the pathologic and microbiologic aspects of the lung in cystic fibrosis (CF), there is a lack of information on the lung localization of bacterial pathogens. Bacteriologic data come from cultures of sputum or accessible lung effluent from bronchoscopy. Our objective was to localize Pseudomonas aeruginosa (PA) in situ in order to provide descriptive data on the relationship between the presence of PA and disease of the surrounding tissue. Using stored, uncut blocks of preserved lung, we deparaffinized, cut, mounted, and reacted them with high-titer rabbit sera made to a mucoid strain of PA. The tissues were then reacted with a second antibody, biotinylated goat antirabbit immunoglobulin, developed using a peroxidase technique and counterstained with hematoxylin. PA organisms stained with heavy brown deposits and this was species-specific. In five patients with CF chronically colonized with PA, the organisms could easily be localized in multiple sections. Microscopic study demonstrated that location was generally endobronchiolar and associated with bronchiolar obliterative changes, mainly in small (less than 1 mm) airways. Extraluminal PA organisms were rare even when there was chronic interstitial inflammation. This study demonstrated the presence of PA at the location where physiologic damage in CF is most severe--the small bronchioles--strengthening the association between PA and pulmonary deterioration in CF.

Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis

“…Therefore, relying on observations made from the pathologic and histopathologic analysis of affected tissues provides substantial insight into the pathogenesis of this disease. Observations of the CF airway epithelium in tissues taken at autopsy or transplant [5][6][7] and observations made during experimental infection of WT and transgenic CF mice [8] clearly show that P. aeruginosa rarely binds to the airway epithelial cells in the CF lung but does so vigorously in mice expressing WT-CFTR (Figure 1a-d).…”

“…One recent study suggested this switch make take as long as 10 years, on average, before mucoid P. aeruginosa is routinely detected by microbiologic cultures [1]. Although many studies, conducted almost exclusively in υitro using cultured cells, have proposed that other P. aeruginosa surface factors such as pili, lectins and other adhesins can influence epithelial cells and initiate such responses as activation of the NF-κB innate immune response pathway associated with subsequent proinflammatory gene expression [40], this does not appear too relevant to CF as P. aeruginosa is never observed to bind to the CF epithelium in υiυo [5][6][7]. Furthermore, this organism only minimally binds to the respiratory epithelium of transgenic CF mice within hours of experimental infection [8].…”

“…However, over-production of alginate remains the hallmark of chronic infection and lung function decline in CF and is a necessary bacterial virulence factor in the pathogenesis of this disease. Overproduction of alginate also reduces P. aeruginosa interactions with the airway epithelium [11], as is seen in lungs of CF patients [5][6][7].…”

“…Therefore, relying on observations made from the pathologic and histopathologic analysis of affected tissues provides substantial insight into the pathogenesis of this disease. Observations of the CF airway epithelium in tissues taken at autopsy or transplant [5][6][7] and observations made during experimental infection of WT and transgenic CF mice [8] clearly show that P. aeruginosa rarely binds to the airway epithelial cells in the CF lung but does so vigorously in mice expressing WT-CFTR (Figure 1a-d).The bacteria in the CF mouse are not observed interacting with the epithelium (Figure 1e,f) but rather found primarily within the mucus (Figure 1g,h), as in CF patients [7], where P. aeruginosa is primarily visualized to be trapped in mucus plugs that predominantly form in the airways [7]. In acutely-infected WT mice, P. aeruginosa cells trapped in the mucus are also readily seen (not shown), but these organisms are effectively cleared from the lung [8].…”

Cartilaginous airway wall dimensions and airway resistance in cystic fibrosis lungs

“…Normal respiratory epithelium forms a protective barrier against colonization by bacteria. Its loss in airways of CF patients has been associated with the presence of Pseudomonas aeruginosa [26]. Airway epithelial injury and repair favour bacterial adherence and may thus contribute to the airway infection in CF [27].…”