Search

Lung infection with Pseudomonas aeruginosa, leading to chronic lung disease with impaired function, is the major course of morbidity and mortality among cystic fibrosis patients. The bacterium produces two lectins that bind to alpha-D-galactose (PA-IL) and L-fucose (PA-IIL), respectively, and lectin-carbohydrate interactions may be involved in microbial pathogenicity by creating bacterial adherence to epithelial and endothelial cells. An ideal animal model for P. aeruginosa infection has until now not been established, but the mink seems to be the only animal that has been reported to develop spontaneous P. aeruginosa infections in the airways. Since cystic fibrosis also severely may affect pancreatic function, we incubated sections from mink lungs and pancreas with a medium containing Pseudomonas lectins in order to detect in situ binding of the bacterial lectins. In the lungs, both lectins adhered to seromucinous glands located in the submucosa of the larger bronchi. Additionally, PA-IL reacted with the capillaries in the alveolar walls and with the small blood vessels forming the vasa vasorum around the larger vessels, while PA-IIL marked the goblet cells in the bronchial surface epithelium. In the pancreas, both lectins bound to the epithelium in the excretory ducts, and additionally, PA-IL strongly stained the pancreatic capillaries while PA-IIL staining was noticed in the apical part of acinar cells in the exocrine part of the gland while no lectin reaction could be recorded in the endocrine cells. Judging from the results in the present paper the mink should be considered a suitable model to study P. aeruginosa adherence.

The opportunistic pathogen Pseudomonas aeruginosa contains lectins of which one of them, PA-IL (gene lecA), shows preference for alpha-galactosylated glycans. The bacterial lectin is probably important in the carbohydrate-mediated adhesion of the microorganism to endothelia and epithelia and thereby the lectin facilitates entering and damaging of the cells. The requirements for the interaction between PA-IL and the carbohydrate epitopes to which the bacterial lectin may bind were here studied using alpha-galactosylated neoglycoproteins that were immobilized on Microtiter plates. It is concluded that the carbohydrate recognizing site of the lectin can have a binding requirement of only one saccharide. Lectin histochemistry was performed on sections from wild type mice and from knock-out mice, which lack function of the alpha1,3-galactosyltransferase gene. All assays with the P. aeruginosa lectin were compared with the results obtained using an isolectin from the legume shrub Griffonia simplicifolia: the GSI-B4 isolectin, which is highly specific for glycans terminating in Galalpha1-R. In the wild-type mice, lectin histochemistry showed a strong capillary reaction in heart, kidney and adrenal gland while none of the two lectins were able to detect capillaries in the pancreas. This could indicate a differential glycosylation with respect to endothelial cell Galalpha epitopes among different organs. Further, since no PA-IL binding to the endothelial cells in the KO mouse was observed, it seems that, in the mouse, the Pseudomonas lectin adheres to the Galalpha1-3Galbeta1-4GlcNAc carbohydrate on endothelial cells in most organs and tissues. Finally, lectin staining of the basement membrane of the acini in the exocrine pancreas suggests the presence of Galalpha1-3Gal epitopes in WT mice basement membranes that are not detected by the P. aeruginosa lectin.