Airway epithelial control of Pseudomonas aeruginosa infection in cystic fibrosis

Defective expression or function of the cystic fibrosis transmembrane conductance regulator (CFTR) underlies the hypersusceptibility of cystic fibrosis (CF) patients to chronic airway infections, particularly with Pseudomonas aeruginosa. CFTR is involved in the specific recognition of P. aeruginosa, thereby contributing to effective innate immunity and proper hydration of the airway surface layer (ASL). In CF, the airway epithelium fails to initiate an appropriate innate immune response, allowing the microbe to bind to mucus plugs that are then not properly cleared because of the dehydrated ASL. Recent studies have identified numerous CFTR-dependent factors that are recruited to the epithelial plasma membrane in response to infection and that are needed for bacterial clearance, a process that is defective in CF patients hypersusceptible to infection with this organism.     

Localization of cystic fibrosis transmembrane conductance regulator to lipid rafts of epithelial cells is required for Pseudomonas aeruginosa-induced cellular activation

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein is an epithelial cell receptor for the outer core oligosaccharide of the Pseudomonas aeruginosa LPS. Bacterial binding leads to CFTR-dependent bacterial internalization, initiation of NF-kappaB nuclear translocation, cellular desquamation, and eventual apoptosis of the infected cells, all of which are critical for innate immune resistance to infection with this pathogen. Lack of this reaction in CF patients underlies their hypersusceptibility to chronic P. aeruginosa infection. In this study we tested whether these epithelial cell responses are dependent upon the localization of CFTR to lipid rafts. Confocal microscopy showed that green fluorescent protein-tagged CFTR (GFP-CFTR) and the lipid raft marker ganglioside GM1 colocalized at sites of P. aeruginosa contact and internalization. GFP-CFTR localized to low density Triton X-100-insoluble fractions in lysates of Madin-Darby canine kidney GFP-CFTR cells, and P. aeruginosa infection increased the levels of GFP-CFTR in these fractions as determined by Western blot. Cells expressing GFP-DeltaF508-CFTR did not have rafts with detectable CFTR protein. Extraction of cell surface cholesterol via cyclodextrin treatment of the cells inhibited CFTR entry into rafts. In addition, cyclodextrin treatment of both human and canine epithelial cells inhibited cellular ingestion of P. aeruginosa, NF-kappaB nuclear translocation, and apoptosis. These results indicate that lipid raft localization of CFTR is required for signaling in response to P. aeruginosa infection. Such signaling is needed for the coordination of innate immunity to P. aeruginosa lung infection, a process that is defective in CF.     

The role of the CFTR in susceptibility to Pseudomonas aeruginosa infections in cystic fibrosis

Recent molecular and cellular studies have shed new light on the basis for the susceptibility of cystic fibrosis (CF) patients to Pseudomonas aeruginosa infection. Changes in airway liquid composition and/or viscosity, enhanced bacterial binding to mucin and epithelial cell receptors, increased innate inflammation owing to disruptions in lipid metabolism and a role for the CFTR protein in bacterial ingestion and clearance have all been postulated. The high P. aeruginosa infection rate in CF patients can potentially be explained by the specificity of the interaction between the CFTR and P. aeruginosa.     

Pseudomonas aeruginosa flagellin and alginate elicit very distinct gene expression patterns in airway epithelial cells: implications for cystic fibrosis disease

Infection with the opportunistic pathogen Pseudomonas aeruginosa remains a major health concern. Two P. aeruginosa phenotypes relevant in human disease include motility and mucoidy. Motility is characterized by the presence of flagella and is essential in the establishment of acute infections, while mucoidy, defined by the production of the exopolysaccharide alginate, is critical in the development of chronic infections, such as the infections seen in cystic fibrosis patients. Indeed, chronic infection of the lung by mucoid P. aeruginosa is a major cause of morbidity and mortality in cystic fibrosis patients. We have used Calu-3 human airway epithelial cells to investigate global responses to infection with motile and mucoid P. aeruginosa. The response of airway epithelial cells to exposure to P. aeruginosa motile strains is characterized by a specific increase in gene expression in pathways controlling inflammation and host defense. By contrast, the response of airway epithelia to the stimuli presented by mucoid P. aeruginosa is not proinflammatory and, hence, may not be conducive to the effective elimination of the pathogen. The pattern of gene expression directed by flagellin, but not alginate, includes innate host defense genes, proinflammatory cytokines, and chemokines. By contrast, infection with alginate-producing P. aeruginosa results in an overall attenuation of host responses and an antiapoptotic effect.     

Cystic fibrosis and innate immunity: how chloride channel mutations provoke lung disease

Innate immunity is essential for prevention of infection in vertebrates and plants and dysfunction of single components of innate immunity may provoke severe disease. Here we describe how mutations in the cystic fibrosis transmembrane conductance regulator gene dysregulate a variety of components of the innate immune system in individuals suffering from the hereditary disease cystic fibrosis. In the airways of these individuals, functions of the mucociliary clearance system, cationic antimicrobial (poly)peptides and neutrophils and macrophages are impaired and inflammatory signal transduction pathways exaggerated. Consequently, chronic airway colonization with opportunistic bacterial pathogens develops and leads to life-threatening lung disease.     

Study of the effect of DNA polymorphisms in the mannose-binding lectin gene (MBL2) on disease severity in Slovak cystic fibrosis patients

Lung infections are the leading cause of morbidity and mortality in cystic fibrosis (CF). Mannose-binding lectin (MBL) is a key factor in innate immunity. We therefore investigated whether MBL2 gene variants are associated with pulmonary function or susceptibility to Pseudomonas aeruginosa and Burkholderia cepacia infection in Slovak patients affected with CF. DNA polymorphisms in exon 1 and the promoter region were typed by single base primer extension assay in 91 patients and 100 healthy controls. The concentrations of MBL protein were determined in 34 patients by a sandwich enzyme-linked immunosorbent assay, and spirometric and microbiological data were collected from medical records. In this study we found that MBL2 genotypes were associated neither with earlier acquisition of P. aeruginosa or B. cepacia nor with reduced pulmonary function among patients. Although MBL2 genotypes were associated with the MBL2 protein serum level, results were statistically significant only for polymorphisms in exon 1, with p = 0.0008. The role of the MBL2 gene in lung disease severity in CF patients represents a very complex phenomenon where both genetic and environmental factors play an important role in addition to that of the MBL2 gene. Understanding this complexity requires further studies based on a broader scale of genetic factors involving both a whole-genome approach and a larger patient cohort.     

Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia.

Respiratory infections with Pseudomonas aeruginosa and Burkholderia cepacia play a major role in the pathogenesis of cystic fibrosis (CF). This review summarizes the latest advances in understanding host-pathogen interactions in CF with an emphasis on the role and control of conversion to mucoidy in P. aeruginosa, a phenomenon epitomizing the adaptation of this opportunistic pathogen to the chronic chourse of infection in CF, and on the innate resistance to antibiotics of B. cepacia, person-to-person spread, and sometimes rapidly fatal disease caused by this organism. While understanding the mechanism of conversion to mucoidy in P. aeruginosa has progressed to the point where this phenomenon has evolved into a model system for studying bacterial stress response in microbial pathogenesis, the more recent challenge with B. cepacia, which has emerged as a potent bona fide CF pathogen, is discussed in the context of clinical issues, taxonomy, transmission, and potential modes of pathogenicity.     

Role of the cystic fibrosis transmembrane conductance regulator in internalization of Pseudomonas aeruginosa by polarized respiratory epithelial cells

Pseudomonas aeruginosa is an important human pathogen, producing lung infection in individuals with cystic fibrosis (CF), patients who are ventilated and those who are neutropenic. The respiratory epithelium provides the initial barrier to infection. Pseudomonas aeruginosa can enter epithelial cells, although the mechanism of entry and the role of intracellular organisms in its life cycle are unclear. We devised a model of infection of polarized human respiratory epithelial cells with P. aeruginosa and investigated the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in adherence, uptake and IL-8 production by human respiratory epithelial cells. We found that a number of P. aeruginosa strains could invade and replicate within cells derived from a patient with CF. Intracellular bacteria did not produce host cell cytotoxicity over a period of 24 h. When these cells were transfected with wild-type CFTR, uptake of bacteria was significantly reduced and release of IL-8 following infection enhanced. We propose that internalized P. aeruginosa may play an important role in the pathogenesis of infection and that, by allowing greater internalization into epithelial cells, mutant CFTR results in an increased susceptibility of bronchial infection with this microbe.     

Sulfatide mediates attachment of Pseudomonas aeruginosa to human pharyngeal epithelial cells

Pseudomonas aeruginosa infections are particularly common in people with cystic fibrosis and despite regular treatment with antibiotics, lung damage due to chronic infection with P. aeruginosa remains the major cause of death in those patients. In order to initiate an infection, P. aeruginosa needs contact with the respiratory epithelial surface and by means of its adhesins i.e., fimbria, hemagglutinins,etc., it recognizes and adheres to the corresponding epithelial receptors. We treated P. aeruginosa strains isolated from sputum of cystic fibrosis patients with several glycolipids such as sulfatide, sulfated ganglioside mixture (GM1a, GD1b, GT1b), asialo-GM1 and galactocerebrosides to determine their effect on attachment with pharyngeal epithelial cells. Sulfated ganglioside mixture and sulfatide inhibited the attachment of P. aeruginosa significantly, whereas asialo-GM1, Gal-Cer and sodium sulfite had no effect on attachment inhibition. This finding suggests that sulfated glycoconjugates found in the extracellular matrix, in mucus and on the surface of epithelial cells of human trachea and lung mediates attachment of P. aeruginosa.     

Polysaccharides serve as scaffold of biofilms formed by mucoid Pseudomonas aeruginosa

Chronic lung infection by mucoid Pseudomonas aeruginosa is one of the major pathologic features in patients with cystic fibrosis. Mucoid P.?aeruginosa is notorious for its biofilm forming capability and resistance to immune attacks. In this study, the roles of extracellular polymeric substances from biofilms formed by mucoid P.?aeruginosa were investigated. Alginate is not an essential structure component for mucoid P.?aeruginosa biofilms. Genetic studies revealed that Pel and Psl polysaccharides serve as essential scaffold and mediate macrocolony formation in mucoid P.?aeruginosa biofilms. The Psl polysaccharide is more important than Pel polysaccharide in mucoid P.?aeruginosa biofilm structure maintenance and phagocytosis resistance. The polysaccharides were further found to protect mucoid P.?aeruginosa strain from host immune clearance in a mouse model of acute lung infection.     

The therapeutic potential of the humoral pattern recognition molecule PTX3 in chronic lung infection caused by Pseudomonas aeruginosa

Chronic lung infections by Pseudomonas aeruginosa strains are a major cause of morbidity and mortality in cystic fibrosis (CF) patients. Although there is no clear evidence for a primary defect in the immune system of CF patients, the host is generally unable to clear P. aeruginosa from the airways. PTX3 is a soluble pattern recognition receptor that plays nonredundant roles in the innate immune response to fungi, bacteria, and viruses. In particular, PTX3 deficiency is associated with increased susceptibility to P. aeruginosa lung infection. To address the potential therapeutic effect of PTX3 in P. aeruginosa lung infection, we established persistent and progressive infections in mice with the RP73 clinical strain RP73 isolated from a CF patient and treated them with recombinant human PTX3. The results indicated that PTX3 has a potential therapeutic effect in P. aeruginosa chronic lung infection by reducing lung colonization, proinflammatory cytokine levels (CXCL1, CXCL2, CCL2, and IL-1β), and leukocyte recruitment in the airways. In models of acute infections and in in vitro assays, the prophagocytic effect of PTX3 was maintained in C1q-deficient mice and was lost in C3- and Fc common γ-chain-deficient mice, suggesting that facilitated recognition and phagocytosis of pathogens through the interplay between complement and FcγRs are involved in the therapeutic effect mediated by PTX3. These data suggested that PTX3 is a potential therapeutic tool in chronic P. aeruginosa lung infections, such as those seen in CF patients.     

Cystic fibrosis pathogens activate Ca2+-dependent mitogen-activated protein kinase signaling pathways in airway epithelial cells

Much of the pulmonary disease in cystic fibrosis is associated with polymorphonuclear leukocyte-dominated airway inflammation caused by bacterial infection. Respiratory epithelial cells express the polymorphonuclear chemokine interleukin-8 (IL-8) in response to ligation of asialylated glycolipid receptors, which are increased on damaged or regenerating cells and those with cystic fibrosis transmembrane conductance regulator mutations. Because both Pseudomonas aeruginosa and Staphylococcus aureus, the most common pathogens in cystic fibrosis, bind asialylated glycolipid receptors such as asialoGM1, we postulated that diverse bacteria can activate a common epithelial signaling pathway to elicit IL-8 expression. P. aeruginosa PAO1 but not pil mutants and S. aureus RN6390 but not the agr mutant RN6911 stimulated increases in [Ca(2+)](i) in 1HAEo- airway epithelial cells. This response stimulated p38 and ERK1/2 mitogen-activated protein kinase (MAPK) signaling cascades resulting in NF-kappaB activation and IL-8 expression. Ligation of the asialoGM1 receptor or thapsigargin-elicited Ca(2+) release activated this pathway, whereas P. aeruginosa lipopolysaccharide did not. The rapid kinetics of epithelial activation precluded bacterial invasion of the epithelium. Recognition of asialylated glycolipid receptors on airway epithelial cells provides a common pathway for Gram-positive and Gram-negative organisms to initiate an epithelial inflammatory response.     

Cutting edge: myeloid differentiation factor 88 is essential for pulmonary host defense against Pseudomonas aeruginosa but not Staphylococcus aureus

Myeloid differentiation factor 88 (MyD88) is an adapter molecule required for signal transduction via Toll-like receptors (TLRs) and receptors of the IL-1 family. Consequently, MyD88-deficient mice are highly susceptible to bacterial infections, including systemic infection with Staphylococcus aureus. To determine the role of MyD88 in innate immunity to bacterial pneumonia, we exposed MyD88-deficient and wild-type mice to aerosolized Pseudomonas aeruginosa or S. aureus. As predicted, MyD88-deficient mice failed to mount an early cytokine or inflammatory response or to control bacterial replication after infection with P. aeruginosa, which resulted in necrotizing pneumonia and death. By contrast, MyD88-deficient mice controlled S. aureus infection despite blunted local cytokine and inflammatory responses. Thus, whereas MyD88-dependent signaling is integral to the initiation of cytokine and inflammatory responses to both pathogens following infection of the lower respiratory tract, MyD88 is essential for innate immunity to P. aeruginosa but not S. aureus.     

Antibiotic therapy of cystic fibrosis in children]

It is postulated that P. aeruginosa in monoculture or in association with Staphylococcus aureus keeps its leading position in chronic bacterial inflammatory broncho-pulmonary processes in children with cystic fibrosis. Antibiotic resistant strains of Burkholderia cepacia, Stenotrophomonas maltophila, Alcaligenes xylosoxidans were revealed (7.1% of the strains). P. aeruginosa strains were susceptible to aminoglycosides, ciprofloxacin, and polymixin B. Susceptibility of smooth and mucoid forms of P. aeruginosa to ceftazidime stayed at the level of 49.6-57.1%. Such microbial associations as P. aeruginosa sm. + S. aureus, P. aeruginosa sm. + P. aeruginosa muc. + S. aureus were mainly susceptible to ciprofloxacin, aminoglycosides and resistant to ceftasidime. Meropenem, cefepim and ciprofloxacin are highly effective antibiotics for the treatment of broncho-pulmonary processes exacerbations at children with chronic P. aeruginosa cystic fibrosis. Intravenous use of antibiotics out of hospital for the treatment of the children with cystic fibrosis is clinically effective, and is economically and psychologically reasonable. It should be used more widely in medical practice.     

Annexin II is a novel receptor for Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa (P. aeruginosa) are critical in ventilated and poly-traumatized patients. Most important, these bacteria cause frequent and chronic pulmonary infections in patients with cystic fibrosis. Therefore, identification of molecular mechanisms that mediate the infection of mammalian cells with P. aeruginosa is urgently required. Here, we aimed to identify novel receptors that are involved in internalization of P. aeruginosa into mammalian epithelial cells. Employing SDS-PAGE purification and mass spectrometry we demonstrate that annexin II specifically binds to P. aeruginosa. The significance of the interaction of annexin II with P. aeruginosa for the infection of mammalian cells is indicated by the finding that neutralization of the ligands on P. aeruginosa by incubation of the bacteria with recombinant, soluble annexin II prevents internalization of P. aeruginosa into human epithelial cells.     

Auxotrophy of Pseudomonas aeruginosa in cystic fibrosis

Seventy-four of 403 (18.4%) sputum isolates of Pseudomonas aeruginosa from 49 of 136 (36.0%) adults with cystic fibrosis (CF) were auxotrophic mutants. Two of 11 (18.2%) isolates of P. aeruginosa taken from patients with non-CF bronchiectasis were also auxotrophic. All 99 strains taken from non-bronchiectatic sources were prototrophic. Forty-six of 55 (83.6%) CF auxotrophs required one or more of 36 growth factors tested; the requirements for the remaining 9 isolates were not identified. Methionine was the sole factor required by 17 of 22 (77.3%) isolated which depended on a single factor. We conclude that auxotrophy is a feature of P. aeruginosa infection in cystic fibrosis.     

Innate immunity mediated by TLR5 as a novel antiinflammatory target for cystic fibrosis lung disease

Novel therapies to target lung inflammation are predicted to improve the lives of people with cystic fibrosis (CF) but specific antiinflammatory targets have not been identified. The goal of this study was to establish whether TLR5 signaling is the key molecular pathway mediating lung inflammation in CF, and to determine whether strategies to inhibit TLR5 can reduce the damaging inflammatory response. The innate immune responses were analyzed in both airway epithelial cells and primary PBMCs from CF patients and matched controls. Additionally, 151 clinical isolates of Pseudomonas aeruginosa from CF patients were assessed for motility and capacity to activate TLR5. Blood and airway cells from CF patients produced significantly more proinflammatory cytokine than did control cells following exposure to the CF pathogens P. aeruginosa and Burkholderia cepacia complex (p < 0.001). Stimulation with pure TLR ligands demonstrated that TLR signaling appears to mediate the excessive cytokine production occurring in CF. Using complementary approaches involving both neutralizing Ab targeting TLR5 and flagellin-deficient bacteria, we established that inhibition of TLR5 abolished the damaging inflammatory response generated by CF airway cells following exposure to P. aeruginosa (p < 0.01). The potential therapeutic value of TLR5 inhibition was further supported by our demonstration that 75% of clinical isolates of P. aeruginosa retained TLR5 activating capacity during chronic CF lung infection. These studies identify the innate immune receptor TLR5 as a novel antiinflammatory target for reducing damaging lung inflammation in CF.