Internalization of Pseudomonas aeruginosa by epithelial respiratory cell lines has been suggested to be dependent on the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Because we have observed intracellular (IC) P. aeruginosa only in cells that do not express apical CFTR, we addressed the question of whether bacterial internalization by epithelial cells depends on the degree of cell differentiation and polarity. Internalization of piliated P. aeruginosa PAO-1 and PAK by human epithelial respiratory cells in primary culture and by the 16 human bronchial epithelial 14o- cell line cultured either on thick collagen gels or on thin collagen films was evaluated by the gentamicin exclusion assay. Cells cultured on thick gels were differentiated, polarized, and tight. They exhibited CFTR at their apical membranes, expressed beta1 integrins at their basal membranes, excluded lanthanum nitrate, and uniformly expressed ZO-1 protein. In contrast, in cells cultured on thin films, CFTR was present mainly in the cytoplasm, whereas beta1 integrins were detected at apical membranes. Most cells cultured on thin films did not exclude lanthanum nitrate and rarely expressed ZO-1 protein. Cells grown on thick and thin collagen substrates differed markedly in bacterial internalization: no IC bacteria could be detected in cells cultured on gels, whereas high IC bacterial concentrations were isolated from cells cultured on thin films. Treatment of cells cultured on thin films with ethylenediaminetetraacetic acid, to disrupt intercellular junctions further, significantly enhanced P. aeruginosa internalization. Our results suggest that P. aeruginosa internalization by epithelial respiratory cells does not depend on CFTR protein expression at the epithelial cell surface but rather on cell polarity and junctional complex integrity.

Fibronectin and a5b1 integrin mediate binding of Pseudomonas aeruginosa to repairing airway epithelium. P. Roger, E. Puchelle, O. Bajolet-Laudinat, J-M. Tournier, C. Debordeaux, M-C. Plotkowski, J.H.M. Cohen, D. Sheppard, and S. de Bentzmann. #ERS Journals Ltd 1999. ABSTRACT: Initial infection of the airway by Pseudomonas aeruginosa may occur through a variety of bacterial strategies including binding to epithelial receptors present at the surface of the respiratory epithelium.In order to characterize the adherence sites for P. aeruginosa in damaged and repairing bronchial tissue, an ex vivo model of airway epithelial injury and repair was developed using primary cell cultures of nasal cells from 14 subjects with polyposis.P. aeruginosa strongly adhered to flattened dedifferentiated (FD) bronchial and nasal cytokeratin 13-positive epithelial cells in the process of migration for repair. In in vitro experiments, competitive binding inhibition assays demonstrated that a5b1 integrins and cellular fibronectin, in particular the RGD sequence, are receptors involved in P. aeruginosa adherence to FD nasal epithelial cells. Fluorescent cell sorting analysis and immunofluorescence techniques revealed that the a5b1 integrins are overexpressed and apically exposed in FD nasal epithelial cells. One 50 kDa outer membrane protein was identified in piliated and nonpiliated strains of P. aeruginosa that was involved in binding to cellular fibronectin and a5b1 epithelial integrins.These results demonstrate that Pseudomonas aeruginosa adherence is related to the dedifferentiation of airway epithelium during the repair process which unmasks and upregulates the a5b1 integrin expression and induces active synthesis of cellular fibronectin. These epithelial receptors are then used by a Pseudomonas aeruginosa 50 kDa outer membrane protein as sites of bacterial adherence. Eur Respir J 1999; 13: 1301±1309.

We investigated the implication of asialo GM1 as an epithelial receptor in the increased Pseudomonas aeruginosa affinity for regenerating respiratory epithelial cells from cystic fibrosis (CF) and non-CF patients. Human respiratory epithelial cells were obtained from nasal polyps of non-CF subjects and of CF patients homozygous for the ⌬F 508 transmembrane conductance regulator protein (CFTR) mutation and cultured according to the explant-outgrowth model. At the periphery of the outgrowth, regenerating respiratory epithelial cells spreading over the collagen I matrix with lamellipodia were observed, characteristic of respiratory epithelial wound repair after injury. P. aeruginosa adherence to regenerating respiratory epithelial cells was found to be significantly greater in the ⌬F 508 homozygous CF group than in the non-CF group (P < 0.001). In vitro competitive binding inhibition assays performed with rabbit polyclonal antibody against asialo GM1 demonstrated that blocking asialo GM1 reduces P. aeruginosa adherence to regenerating respiratory epithelial cells in ⌬F 508 homozygous CF cultures (P < 0.001) as well as in non-CF cultures (P < 0.001). Blocking of asialo GM1 was significantly more efficient in CF patients than in non-CF subjects (P < 0.05). Distribution of asialo GM1 as determined by preembedding labelling and immunoelectron microscopy clearly demonstrated the specific apical membrane expression of asialo GM1 by regenerating respiratory epithelial cells, whereas other cell phenotypes did not apically express asialo GM1. These results demonstrate that (i) asialo GM1 is an apical membrane receptor for P. aeruginosa expressed at the surface of CF and non-CF regenerating respiratory epithelial cells and (ii) asialo GM1 is specifically recovered in regenerating respiratory epithelium. These results suggest that in CF, epithelial repair represents the major event which exposes asialo GM1 for P. aeruginosa adherence.

P Ps se eu ud do om mo on na as s a ae er ru ug gi in no os sa a a ad dh he er re en nc ce e t to o r re em mo od de el ll li in ng g r re es sp pi ir ra at to or ry y e ep pi it th he el li iu um m Normal respiratory epithelium is protected against bacteria via mucus and mucociliary clearance. Alteration of mucociliary clearance and of glycosylation of mucins in CF facilitates the access of bacteria to the underlying airway epithelial cells. Intact respiratory epithelium does not bind P. aeruginosa, whereas injured respiratory epithelium is highly susceptible to P. aeruginosa adherence. We found that the high affinity of respiratory epithelium, from CF and non-CF sources, for P. aeruginosa, during the wound repair process is related to the apical expression of asialo ganglioside M1 (aG M1 ). The affinity of repairing respiratory epithelium for P. aeruginosa is time-dependent, and is related to transient apical expression of aG M1 at the surface of repairing respiratory epithelial cells. CF respiratory epithelial cells apically express more aG M1 residues with relation to an increased affinity for P. aeruginosa than non-CF cells.High epithelial damage followed by repair represents a major cause of P. aeruginosa adherence to airway epithelium in cystic fibrosis. However, P. aerurignosa adherence and colonization are not restricted to cystic fibrosis disease and P. aeruginosa pneumonia may also occur in severely immunocompromised patients, suggesting that epithelial injury and decreased host-response favour the colonization of the airways by P. aeruginosa.