Pseudomonas aeruginosa exoenzyme S induces transcriptional expression of proinflammatory cytokines and chemokines

Biofilm-derived membrane vesicles exhibit potent immunomodulatory activity in Pseudomonas aeruginosa PAO1

Pathogenic bacteria form biofilms on epithelial cells, and most bacterial biofilms show increased production of membrane vesicles (MVs), also known as outer membrane vesicles in Gram-negative bacteria. Numerous studies have investigated the MVs released under planktonic conditions; however, the impact of MVs released from biofilms on immune responses remains unclear. This study aimed to investigate the characteristics and immunomodulatory activity of MVs obtained from both planktonic and biofilm cultures of Pseudomonas aeruginosa PAO1. The innate immune responses of macrophages to planktonic-derived MVs (p-MVs) and biofilm-derived MVs (b-MVs) were investigated by measuring the mRNA expression of proinflammatory cytokines. Our results showed that b-MVs induced a higher expression of inflammatory cytokines, including Il1b, Il6, and Il12p40, than p-MVs. The mRNA expression levels of Toll-like receptor 4 (Tlr4) differed between the two types of MVs, but not Tlr2. Polymyxin B significantly neutralized b-MV-mediated cytokine induction, suggesting that lipopolysaccharide of native b-MVs is the origin of the immune response. In addition, heat-treated or homogenized b-MVs induced the mRNA expression of cytokines, including Tnfa, Il1b, Il6, and Il12p40. Heat treatment of MVs led to increased expression of Tlr2 but not Tlr4, suggesting that TLR2 ligands play a role in detecting the pathogen-associated molecular patterns in lysed MVs. Taken together, our data indicate that potent immunomodulatory MVs are produced in P. aeruginosa biofilms and that this behavior could be a strategy for the bacteria to infect host cells. Furthermore, our findings would contribute to developing novel vaccines using MVs.

Interesting Cytokine Profile Caused by Clinical Strains of Pseudomonas aeruginosa MDR Carrying the exoU Gene

Pseudomonas aeruginosa is an opportunistic pathogen in HAIs with two facets: the most studied is the high rate of antimicrobial resistance, and the less explored is the long list of virulence factors it possesses. This study aimed to characterize the virulence genes carried by strains as well as the profile of cytokines related to inflammation, according to the resistance profile presented. This study aims to identify the virulence factors associated with MDR strains, particularly those resistant to carbapenems, and assess whether there is a cytokine profile that correlates with these characteristics. As methodology species were identified by classical microbiological techniques and confirmed by molecular biology, resistance levels were determined by the minimum inhibitory concentration and identification of MDR strains. Virulence factor genotyping was performed using PCR. In addition, biofilm production was assessed using crystal violet staining. Finally, the strains were cocultured with PBMC, and cell survival and the cytokines IL-1β, IL-6, IL-10, IL-8, and TNF-α were quantified using flow cytometry. Bacteremia and nosocomial pneumonia in adults are the most frequent types of infection. In the toxigenic aspect, genes corresponding to the type III secretion system were present in at least 50% of cases. In addition, PBMC exposed to strains of four different categories according to their resistance and toxicity showed a differential pattern of cytokine expression, a decrease in IL-10, IL-6, and IL-8, and an over-secretion of IL-1b. In conclusion, the virulence genes showed a differentiated appearance for the two most aggressive exotoxins of T3SS (exoU and exoS) in multidrug-resistant strains. Moreover, the cytokine profile displays a low expression of cytokines with anti-inflammatory and proinflammatory effects in strains carrying the exoU gene.

Investigation of virulence factors in Pseudomonas aeruginosa isolates by phenotypic and genotypic methods

INTRODUCTION

Pseudomonas aeruginosa possesses a variety of virulence factors that may contribute to its pathogenicity, and relationship has been determined between antibiotic resistance and biofilm. The aim of this study was to investigate the virulence factors of Pseudomonas aeruginosa isolates by genotypic and phenotypic methods, as well as whether there is a relationship between other virulence factors and antibiotic resistance.

METHODS

A total of 80 Pseudomonas aeruginosa strains were sent from various clinics included in the study. Identification and antibiotic resistance profile of isolates were determined by Vitek 2 (Biomerioux, France) automated system. Pseudomonas P agar, Pseudomonas F agar, and motility test medium were used for phenotyping tests. Tox A, Exo S, Plc N, and Las B were evaluated with Real-time PCR (Anatolia, Geneworks, Turkey).

RESULTS

The highest rates of antibiotic resistance were observed against imipenem (42.5%) and meropenem (40%). Among the isolates, 81.3% tested positive for Tox A, 30% for Exo S, 32.5% for Plc N, and 42.5% for Las B. Additionally, 70.4% of the isolates tested positive for pyocyanin, 41.3% for pyoverdine, 1.8% for pyorubin, and 8.9% tested negative for pyorubin. No statistically significant difference was found between antibiotic resistance and the presence of virulence factors (p > 0.005).

CONCLUSIONS

The relationship between antibiotic resistance and virulence factors is controversial. There are studies demonstrating the relationship between virulence factors and antibiotic resistance, as well as studies that indicate the absence of such a relationship. Investigating virulence and antibiotic resistance rates may be important for identifying potential drug targets for subsequent research.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

CLEC5A is critical in Pseudomonas aeruginosa-induced acute lung injury

Pseudomonas aeruginosa is one of the most common nosocomial infections worldwide, and it frequently causes ventilator-associated acute pneumonia in immunocompromised patients. Abundant neutrophil extracellular traps (NETs) contribute to acute lung injury, thereby aggravating ventilator-induced lung damage. While pattern recognition receptors (PRRs) TLR4 and TLR5 are required for host defense against P. aeruginosa invasion, the PRR responsible for P. aeruginosa–induced NET formation, proinflammatory cytokine release, and acute lung injury remains unclear. We found that myeloid C-type lectin domain family 5 member A (CLEC5A) interacts with LPS of P. aeruginosa and is responsible for P. aeruginosa–induced NET formation and lung inflammation. P. aeruginosa activates CLEC5A to induce caspase-1–dependent NET formation, but it neither causes gasdermin D (GSDMD) cleavage nor contributes to P. aeruginosa–induced neutrophil death. Blockade of CLEC5A attenuates P. aeruginosa–induced NETosis and lung injury, and simultaneous administration of anti-CLEC5A mAb with ciprofloxacin increases survival rate and decreases collagen deposition in the lungs of mice challenged with a lethal dose of P. aeruginosa. Thus, CLEC5A is a promising therapeutic target to reduce ventilator-associated lung injury and fibrosis in P. aeruginosa–induced pneumonia.

Circulating microRNA sequencing revealed miRNome patterns in hematology and oncology patients aiding the prognosis of invasive aspergillosis

Invasive aspergillosis (IA) may occur as a serious complication of hematological malignancy. Delays in antifungal therapy can lead to an invasive disease resulting in high mortality. Currently, there are no well-established blood circulating microRNA biomarkers or laboratory tests which can be used to diagnose IA. Therefore, we aimed to define dysregulated miRNAs in hematology and oncology (HO) patients to identify biomarkers predisposing disease. We performed an in-depth analysis of high-throughput small transcriptome sequencing data obtained from the whole blood samples of our study cohort of 50 participants including 26 high-risk HO patients and 24 controls. By integrating in silico bioinformatic analyses of small noncoding RNA data, 57 miRNAs exhibiting significant expression differences (P < 0.05) were identified between IA-infected patients and non-IA HO patients. Among these, we found 36 differentially expressed miRNAs (DEMs) irrespective of HO malignancy. Of the top ranked DEMs, we found 14 significantly deregulated miRNAs, whose expression levels were successfully quantified by qRT-PCR. MiRNA target prediction revealed the involvement of IA related miRNAs in the biological pathways of tumorigenesis, the cell cycle, the immune response, cell differentiation and apoptosis.

CrkII/Abl phosphorylation cascade is critical for NLRC4 inflammasome activity and is blocked by Pseudomonas aeruginosa ExoT

Type 3 Secretion System (T3SS) is a highly conserved virulence structure that plays an essential role in the pathogenesis of many Gram-negative pathogenic bacteria, including Pseudomonas aeruginosa. Exotoxin T (ExoT) is the only T3SS effector protein that is expressed in all T3SS-expressing P. aeruginosa strains. Here we show that T3SS recognition leads to a rapid phosphorylation cascade involving Abl / PKCδ / NLRC4, which results in NLRC4 inflammasome activation, culminating in inflammatory responses that limit P. aeruginosa infection in wounds. We further show that ExoT functions as the main anti-inflammatory agent for P. aeruginosa in that it blocks the phosphorylation cascade through Abl / PKCδ / NLRC4 by targeting CrkII, which we further demonstrate to be important for Abl transactivation and NLRC4 inflammasome activation in response to T3SS and P. aeruginosa infection.

Pseudomonas aeruginosa secretes the toxin ExoT, which is important for pathogenesis. Here, the authors show that ExoT inhibits NLRC4-dependent inflammatory responses during wound infection.

Ocular Permeation of Topical Tazocin and Its Effectiveness in the Treatment of Pseudomonas aeruginosa Induced Keratitis in Rabbits

PURPOSE

Pseudomonas aeruginosa is the most common causative organism for contact lens-associated corneal ulcer and is commonly treated with fluoroquinolones. With the emergence of resistant strains, it is important to investigate alternative therapies. Despite well-established efficacy of tazocin against systemic Pseudomonas infections, its topical use for the treatment of Pseudomonas keratitis has not been described, hence this study was aimed to find the ocular permeation of Tazocin and its efficacy in treating keratitis in rabbit eyes.

METHODS

We investigated the ocular permeation of topical tazocin after single drop application in normal rabbit eyes by estimating piperacillin and tazobactam concentrations in cornea, aqueous, and vitreous using a validated LC-MS/MS method. Furthermore, we determined the efficacy of repeated dose administration of tazocin against experimentally induced P. aeruginosa keratitis in rabbits in comparison to moxifloxacin. To determine the efficacy, clinical examination, histopathological examination, and estimation of bacterial load and inflammatory cytokines in cornea were done.

RESULTS

Significant corneal concentration of piperacillin and tazobactam was detected in normal rabbit corneas after single dose treatment with tazocin. In rabbits with Pseudomonas-induced keratitis, topical tazocin caused significant clinical and histopathological improvement. This improvement was associated with reduction in corneal bacterial load and inflammatory cytokines. Compared to moxifloxacin 0.5%, tazocin treated group showed greater clinical response which was associated with higher interleukin (IL)-1β, lower tumor necrosis factor (TNF)-α, a comparable level of IL-8, greater reduction in corneal bacterial load, and lesser inflammatory cell infiltration.

CONCLUSION

Tazocin showed good ocular penetration and was effective in treatment of Pseudomonas induced keratitis in rabbits.

Possible mechanisms of Pseudomonas aeruginosa-associated lung disease

Pseudomonas aeruginosa is an opportunistic bacterium causing lung injury in immunocompromised patients correlated with high morbidity and mortality. Many bacteria, including P. aeruginosa, use extracellular signals to synchronize group behaviors, a process known as quorum sensing (QS). In the P. aeruginosa complex QS system controls expression of over 300 genes, including many involved in host colonization and disease. P. aeruginosa infection elicits a complex immune response due to a large number of immunogenic factors present in the bacteria or released during infection. Here, we focused on the mechanisms by which P. aeruginosa triggers lung injury and inflammation, debating the possible ways that P. aeruginosa evades the host immune system, which leads to immune suppression and resistance.

Pathogenic Escherichia coli and lipopolysaccharide enhance the expression of IL-8, CXCL5, and CXCL10 in canine endometrial stromal cells

Chemokines play a central role in cellular communication in response to bacterial infection. However, the knowledge of the chemokine responses to bacterial infections in dogs remains limited. Uterine bacterial infection (pyometra) is one of the most common bacterial diseases in dogs and causes sepsis in most of the cases. We have shown previously that dogs with pyometra have higher messenger RNA (mRNA) levels of chemokines in uterus. To assess whether the stromal part of the endometrium expresses chemokines in response to bacterial infection, we cultured endometrial stromal cells isolated from healthy dogs and exposed them to either live pathogenic Escherichia coli, isolated from the uterus of a dog with pyometra, or lipopolysaccharide. Changes in the mRNA expression of ELR(+) CXC chemokines, IL-8, CXCL5, CXCL7, and ELR(-) CXC chemokine, CXCL10, were measured after 24 hours using quantitative real-time polymerase chain reaction. Levels of IL-8, CXCL5, and CXCL10 were upregulated in endometrial stromal cells exposed to E coli and lipopolysaccharide, whereas the level of CXCL7 was decreased or unaffected. In addition, levels of IL-8 and CXCL5, but not CXCL7 or CXCL10, were significantly higher in dogs with pyometra than those in healthy dogs. Our findings show that pathogenic uterine-derived E coli induces a CXC chemokine response both in cultured endometrial stromal cells within 24 hours and in pyometra-affected uteri from dogs. Stromal cells could therefore play an important role in early neutrophil and T cell recruitment to the site of inflammation during gram-negative bacterial infection of the uterus. Further studies are needed to clarify the role of chemokines in host response to bacterial infection in dogs and the possibility of using chemokines as diagnostic parameters for bacterial infection in this species.

Non-invasive assessment of upper and lower airway infection and inflammation in CF patients

BACKGROUND

The upper (UAW) and lower (LAW) airways of patients with cystic fibrosis (CF) have the same ion-channel defects, but little is known about similarities and differences in host immunological responses at the two levels.

AIM

Identification and comparison of both levels' pathogen colonization and resulting immunological host responses.

METHODS

The UAW and LAW of 40 CF patients were non-invasively assessed by nasal lavage and induced sputum. Pathogen colonization, cytology, and the concentrations of inflammatory mediators (TNF-α, MPO, matrix metalloprotease (MMP)-9, tissue inhibitor of metalloprotease (TIMP)-1, regulated upon activation, normal T-cell expressed and presumably secreted (RANTES), and interleukin (IL)-1β, -5, -6, -8, and -10) were measured.

RESULTS

Inflammatory responses were more pronounced in the LAW than the UAW. Pseudomonas aeruginosa LAW colonization is accompanied by a significantly enhanced neutrophil (PMN)-dominated response (P = 0.041) and IL-8 concentration (P = 0.01) not observed in P. aeruginosa UAW colonization. In contrast, sinonasal P. aeruginosa colonization resulted in elevated RANTES (P = 0.039) and reduced MMP-9 (P = 0.023) and TIMP-1 (P = 0.035) concentrations. Interestingly, LAW P. aeruginosa colonization was associated with reduced sinonasal concentrations of MMP-9 (P = 0.01) and TIMP-1 (P = 0.02), a finding independent of UAW colonization for MMP-9.

CONCLUSION

CF UAW and LAW show distinct inflammatory profiles and differentiated responses upon P. aeruginosa colonization. Assessment of UAW colonization and MMP-9 are predictive of chronic pulmonary colonization with P. aeruginosa. Thus, this linkage between CF UAW and LAW can provide new clinical and scientific implications.

Anti-PcrV antibody in cystic fibrosis: a novel approach targeting Pseudomonas aeruginosa airway infection

Pseudomonas aeruginosa (Pa) airway infection is associated with increased morbidity and mortality in cystic fibrosis (CF). The type III secretion system is one of the factors responsible for the increased virulence and pro-inflammatory effects of Pa. KB001 is a PEGylated, recombinant, anti-Pseudomonas-PcrV antibody Fab' fragment that blocks the function of Pa TTSS. We studied the safety, pharmacokinetic (PK), and pharmacodynamic properties of KB001 in CF subjects with chronic Pa infection. Twenty-seven eligible CF subjects (≥12 years of age, FEV1 ≥40% of predicted, and sputum Pa density >10(5)  CFU/g) received a single intravenous dose of KB001 (3 mg/kg or 10 mg/kg) or placebo. Safety, PK, Pa density, clinical outcomes, and inflammatory markers were assessed. KB001 had an acceptable safety profile and a mean serum half-life of 11.9 days. All subjects had Pa TTSS expression in sputum. There were no significant differences between KB001 and placebo for changes in Pa density, symptoms, or spirometry after a single dose. However, compared to baseline, at Day 28 there was a trend towards a dose-dependent reduction in sputum myeloperoxidase, IL-1, and IL-8, and there were significant overall differences in change in sputum neutrophil elastase and neutrophil counts favoring the KB001 10 mg/kg group versus placebo (-0.61 log(10) and -0.63 log(10) , respectively; P < 0.05). These results support targeting Pa TTSS with KB001 as a nonantibiotic strategy to reduce airway inflammation and damage in CF patients with chronic Pa infection. Repeat-dosing studies are necessary to evaluate the durability of the anti-inflammatory effects and how that may translate into clinical benefit. (NCT00638365).

Dynamics of soluble and cellular inflammatory markers in nasal lavage obtained from cystic fibrosis patients during intravenous antibiotic treatment

BACKGROUND

In cystic fibrosis (CF) patients, the upper airways display the same ion channel defect as evident in the lungs, resulting in chronic inflammation and infection. Recognition of the sinonasal area as a site of first and persistent infection with pathogens, such as Pseudomonas aeruginosa, reinforces the "one-airway" hypothesis. Therefore, we assessed the effect of systemic antibiotics against pulmonary pathogens on sinonasal inflammation.

METHODS

Nasal lavage fluid (NLF) from 17 CF patients was longitudinally collected prior to and during elective intravenous (i.v.) antibiotic treatment to reduce pathogen burden and resulting inflammation (median treatment time at time of analysis: 6 days). Samples were assessed microbiologically and cytologically. Cytokine and chemokine expression was measured by Cytometric Bead Array and ELISA (interleukin (IL)-1β, IL-6, IL-8, MPO, MMP9, RANTES and NE). Findings were compared with inflammatory markers from NLF obtained from 52 healthy controls.

RESULTS

Initially, the total cell count of the NLF was significantly higher in CF patients than in controls. However after i.v. antibiotic treatment it decreased to a normal level. Compared with controls, detection frequencies and absolute concentrations of MPO, IL-8, IL-6 and IL-1β were also significantly higher in CF patients. The detection frequency of TNF was also higher. Furthermore, during i.v. therapy sinonasal concentrations of IL-6 decreased significantly (P = 0.0059), while RANTES and MMP9 levels decreased 10-fold and two-fold, respectively. PMN-Elastase, assessed for the first time in NFL, did not change during therapy.

CONCLUSIONS

Analysis of NLF inflammatory markers revealed considerable differences between controls and CF patients, with significant changes during systemic i.v. AB treatment within just 6 days. Thus, our data support further investigation into the collection of samples from the epithelial surface of the upper airways by nasal lavage as a potential diagnostic and research tool.

A novel Pseudomonas aeruginosa-derived effector cooperates with flagella to mediate the upregulation of interleukin 8 in human epithelial cells

Infection with Pseudomonas aeruginosa results in a massive accumulation of neutrophils in response to prolonged and sustained expression of inflammatory mediators. The major chemokine associated with this excessive neutrophil recruitment is IL-8, the accumulation of which is a hallmark of cornea and cystic fibrosis airway inflammation. To date, several P. aeruginosa-associated and extracellular factors required for the stimulation of IL-8 expression have been identified. Here, we report a novel effector molecule, nucleoside diphosphate kinase (Ndk), which increases the expression of IL-8 by translocating into host cells. The induction appears to be dependent on both the kinase activity of Ndk and an additional bacterial factor, flagellin, via an NF-κB signaling pathway. This study demonstrates the role of a novel effector, Ndk, which is capable of inducing prominent inflammatory chemokine IL-8 expression with the aid of flagellin during P. aeruginosa infection.

Structure and function of the Type III secretion system of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a dangerous pathogen particularly because it harbors multiple virulence factors. It causes several types of infection, including dermatitis, endocarditis, and infections of the urinary tract, eye, ear, bone, joints and, of particular interest, the respiratory tract. Patients with cystic fibrosis, who are extremely susceptible to Pseudomonas infections, have a bad prognosis and high mortality. An important virulence factor of P. aeruginosa, shared with many other gram-negative bacteria, is the type III secretion system, a hollow molecular needle that transfers effector toxins directly from the bacterium into the host cell cytosol. This complex macromolecular machine works in a highly regulated manner and can manipulate the host cell in many different ways. Here we review the current knowledge of the structure of the P. aeruginosa T3SS, as well as its function and recognition by the immune system. Furthermore, we describe recent progress in the development and use of therapeutic agents targeting the T3SS.

Expression of IL-23, VEGF and TLR2/TLR4 on mononuclear cells after exposure to Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative, aerobic bacillus causing infections of the respiratory and other organ systems in susceptible hosts. Although it does not cause pulmonary infections in immunocompetent individuals, P. aeruginosa causes chronic lung infection in individuals with cystic fibrosis and nosocomial pneumonia resulting in significant morbidity and mortality. Exogenous administration of an important P. aeruginosa virulence factor, lipase, present in P. aeruginosa culture supernatant, induces potent mononuclear cell activation leading to the production of numerous proinflammatory cytokines. In particular, P. aeruginosa culture supernatant stimulated increased proliferation of THP-1 cells and monocytes (MN). The addition of culture supernatant to THP-1 cells and MN also induced Interleukin (IL)-23 and vascular endothelial growth factor (VEGF) release in a time-dependent manner. To investigate whether any compounds present in the supernatant lipase contributed to releasing IL-23 and VEGF, the culture supernatant from P. aeruginosa containing lipase was treated with hexadecylsulfonylfluoride (AMSF). The AMSF-treated culture supernatant (CS) did not show any induction on the IL-23 and VEGF release compared to the cells treated with CS without AMSF. We also showed that Toll-like receptors (TLR)2/TLR4 are expressed in THP-1 cells and MN treated with P. aeruginosa CS in a time-dependent fashion. Flow cytometry analysis revealed a higher TLR4 and a lower TLR2 expression at 48 and 72 h of treatment. The treatment of cells with TLR4 neutralizing antibody, and to a lesser extent with TLR2 neutralizing antibody, resulted in a decrease in P. aeruginosa CS-induced IL-23 and VEGF production.

Corr4A and VRT325 do not reduce the inflammatory response to P. aeruginosa in human cystic fibrosis airway epithelial cells

BACKGROUND

P. aeruginosa chronically colonizes the lung in CF patients and elicits a proinflammatory response. Excessive secretion of IL-6 and IL-8 by CF airway cells in response to P. aeruginosa infection in the CF airway is though to contribute to lung injury. Accordingly, the goal of this study was to test the hypothesis that Corr4a and VRT325, investigational compounds that increase DeltaF508-CFTR mediated Cl(-) secretion in human CF airway cells, reduce the pro-inflammatory response to P. aeruginosa.

METHODS

IL-6 and IL-8 secretion by polarized CF human airway epithelial cells (CFBE41o-) were measured by multiplex analysis, and DeltaF508-CFTR Cl- secretion was measured in Ussing chambers. Airway cells were exposed to P. aeruginosa (PAO1 or PA14) and Corr4a or VRT325.

RESULTS

Corr4a and VRT325 increased DeltaF508-CFTR Cl(-) secretion but did not reduce either constitutive IL-6 or IL-8 secretion, or IL-6 and IL-8 secretion stimulated by P. aeruginosa (PA14 or PAO1).

CONCLUSIONS

Corr4a and VRT325 do not reduce the inflammatory response to P. aeruginosa in human cystic fibrosis airway epithelial cells.

Pseudomonas aeruginosa induces interleukin-8 (IL-8) gene expression in human conjunctiva through the recruitment of both RelA and CCAAT/enhancer-binding protein beta to the IL-8 promoter

The purpose of this study was to identify the Pseudomonas aeruginosa-activated signaling pathway leading to interleukin (IL)-8 gene expression and protein synthesis by human conjunctival epithelium. IL-8 protein and mRNA were determined by enzyme-linked immunosorbent assay and reverse transcription-PCR, respectively. Activation of MAPKs and NF-kappaB was analyzed by Western blotting using phosphospecific antibodies. We used transfection with wild-type or mutated IL-8 promoters and cotransfection with transcription factor overexpressing plasmids or small interfering RNAs. Electrophoretic mobility shift assay and chromatin immunoprecipitation (ChIP) were performed for in vitro and in vivo protein-DNA binding studies, respectively. P. aeruginosa increased IL-8 expression at the transcriptional level by phosphorylating CCAAT/enhancer-binding protein beta (C/EBPbeta) via p38MAPK and activating NF-kappaB. The simultaneous involvement of RelA and C/EBPbeta and the integrity of the corresponding consensus sites were required, whereas c-Jun was involved only in basal IL-8 expression. Re-ChIP experiments showed that RelA and C/EBPbeta act together at the IL-8 promoter level upon P. aeruginosa infection. Taken together, our results suggest that P. aeruginosa induces IL-8 promoter expression and protein production in conjunctival epithelial cells by activating RelA and C/EBPbeta and by promoting the cooperative binding of these transcription factors to the IL-8 promoter that in turn activates transcription.

The type III pseudomonal exotoxin U activates the c-Jun NH2-terminal kinase pathway and increases human epithelial interleukin-8 production

Microbial interactions with host cell signaling pathways are key determinants of the host cell response to infection. Many toxins secreted by bacterial type III secretion systems either stimulate or inhibit the host inflammatory response. We investigated the role of type III secreted toxins of the lung pathogen Pseudomonas aeruginosa in the inflammatory response of human respiratory epithelial cells to infection. Using bacteria with specific gene deletions, we found that interleukin-8 production by these cells was almost entirely dependent on bacterial type III secretion of exotoxin U (ExoU), a phospholipase, although other bacterial factors are involved. ExoU activated the c-Jun NH(2)-terminal kinase pathway, stimulating the phosphorylation and activation of mitogen-activated kinase kinase 4, c-Jun NH(2)-terminal kinase, and c-Jun. This in turn increased levels of transcriptionally competent activator protein-1. Although this pathway was dependent on the lipase activity of ExoU, it was independent of cell death. Activation of mitogen-activated kinase signaling by ExoU in this fashion is a novel mechanism by which a bacterial product can initiate a host inflammatory response, and it may result in increased epithelial permeability and bacterial spread.

Cytokines in exhaled breath condensate of children with asthma and cystic fibrosis

BACKGROUND

Inflammatory mediators in exhaled breath condensate (EBC) indicate ongoing inflammation in the lungs and might differentiate between asthma and cystic fibrosis (CF).

OBJECTIVES

To evaluate the presence, concentration, and short-term variability of TH1- and TH2-mediated cytokines (interferon-gamma [IFN-gamma], tumor necrosis factor alpha [TNF-alpha], interleukin 10 [IL-10], IL-5, IL-4, and IL-2) in EBC of children with asthma or CF and in controls and to analyze the discriminating ability of inflammatory markers in EBC between children with asthma or CF and controls.

METHODS

Expired air was conducted through a double-jacketed glass tube cooled by circulating ice water. In 33 asthmatic children, 12 children with CF, and 35 control children, EBC was collected during tidal breathing. Cytokines were measured using flow cytometry.

RESULTS

Interleukin 2, IL-4, IFN-gamma, and IL-10 were detected in 16%, 16%, 11%, and 9%, respectively, of all samples in asthma and CF. Interleukin 5 and TNF-alpha were not detected in children with CF. Cytokine concentrations did not differ significantly in children with asthma vs CF. In controls, IFN-gamma, TNF-alpha, and IL-10 were detected in 9%, 14%, and 3%, respectively; IL-2, IL-4, and IL-5 were not detected in controls.

CONCLUSIONS

Cytokines such as IFN-gamma, TNF-alpha, IL-10, IL-5, IL-4, and IL-2 can be detected in EBC of children with asthma or CF. However, the concentrations found are close to the detection limits of the assay used. These findings emphasize the importance of developing more sensitive techniques for the analysis of EBC and of standardizing the EBC collection method.

Different domains of Pseudomonas aeruginosa exoenzyme S activate distinct TLRs

Some bacterial products possess multiple immunomodulatory effects and thereby complex mechanisms of action. Exogenous administration of an important Pseudomonas aeruginosa virulence factor, exoenzyme S (ExoS) induces potent monocyte activation leading to the production of numerous proinflammatory cytokines and chemokines. However, ExoS is also injected directly into target cells, inducing cell death through its multiple effects on signaling pathways. This study addresses the mechanisms used by ExoS to induce monocyte activation. Exogenous administration resulted in specific internalization of ExoS via an actin-dependent mechanism. However, ExoS-mediated cellular activation was not inhibited if internalization was blocked, suggesting an alternate mechanism of activation. ExoS bound a saturable and specific receptor on the surface of monocytic cells. ExoS, LPS, and peptidoglycan were all able to induce tolerance and cross-tolerance to each other suggesting the involvement of a TLR in ExoS-recognition. ExoS activated monocytic cells via a myeloid differentiation Ag-88 pathway, using both TLR2 and the TLR4/MD-2/CD14 complex for cellular activation. Interestingly, the TLR2 activity was localized to the C-terminal domain of ExoS while the TLR4 activity was localized to the N-terminal domain. This study provides the first example of how different domains of the same molecule activate two TLRs, and also highlights the possible overlapping pathophysiological processes possessed by microbial toxins.

Dysregulation of IL-2 and IL-8 production in circulating T lymphocytes from young cystic fibrosis patients

It is well documented that patients with cystic fibrosis (CF) are unable to clear persistent airway infections in spite of strong local inflammation, suggesting a dysregulation of immunity in CF. We and others have reported previously that T lymphocytes may play a prominent role in this immune imbalance. In the present work, we compared the reactivity of CD3+ T cells obtained from young CF patients in stable clinical conditions (n = 10, aged 9-16.5 years) to age-matched healthy subjects (n = 6, aged 9-13.5 years). Intracellular levels of interferon (IFN)-gamma, interleukin (IL)-2, IL-8 and IL-10 were determined by flow cytometry after whole blood culture. The data identified T lymphocyte subsets producing either low levels (M1) or high levels (M2) of cytokine under steady-state conditions. We found that the production of IFN-gamma and IL-10 by T lymphocytes was similar between young CF patients and healthy subjects. In contrast, after 4 h of activation with PMA and ionomycin, the percentage of T cells producing high levels of IL-2 (M2) was greater in CF patients (P = 0.02). Moreover, T cells from CF patients produced lower levels of IL-8, before and after activation (P = 0.007). We conclude that a systemic immune imbalance is present in young CF patients, even when clinically stable. This disorder is characterized by the capability of circulating T lymphocytes to produce low levels of IL-8 and by the emergence of more numerous T cells producing high levels of IL-2. This imbalance may contribute to immune dysregulation in CF.

Preferential Diaphragmatic Weakness during SustainedPseudomonas aeruginosaLung Infection

Infection with Pseudomonas aeruginosa plays a major role in the pulmonary inflammation and injury associated with cystic fibrosis. Lung inflammation may also lead to more widespread systemic effects on other organs. We tested the following hypotheses: (1) ongoing P. aeruginosa lung infection produces diaphragmatic and limb muscle weakness and (2) such muscle dysfunction is directly correlated with the level of pulmonary inflammation. Chronic bronchopulmonary infection with mucoid P. aeruginosa was induced in C57BL/6 mice. At Day 2 after infection, diaphragmatic force was decreased (37%) only in mice infected with a high dose of 1 x 10(6) cfu, whereas by Day 7 after infection, diaphragmatic force was similarly reduced (36%) even at a fivefold lower inoculating dose. No significant correlations were found between diaphragmatic weakness and pulmonary inflammation, as assessed by the number of neutrophils, macrophages, and lymphocytes in bronchoalveolar lavage fluid. Moreover, in marked contrast to the diaphragm, no effects of P. aeruginosa infection on contractile function were observed in prototypical slow- and fast-twitch hindlimb muscles. We conclude that sustained lung infection with P. aeruginosa induces preferential weakness of the diaphragm, which is not directly correlated with the degree of pulmonary inflammation induced under these conditions.

Effector ExoU from the type III secretion system is an important modulator of gene expression in lung epithelial cells in response to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an important pathogen in immunocompromised patients and secretes a diverse set of virulence factors that aid colonization and influence host cell defenses. An important early step in the establishment of infection is the production of type III-secreted effectors translocated into host cells by the bacteria. We used cDNA microarrays to compare the transcriptomic response of lung epithelial cells to P. aeruginosa mutants defective in type IV pili, the type III secretion apparatus, or in the production of specific type III-secreted effectors. Of the 18,000 cDNA clones analyzed, 55 were induced or repressed after 4 h of infection and could be classified into four different expression patterns. These include (i) host genes that are induced or repressed in a type III secretion-independent manner (32 clones), (ii) host genes induced specifically by ExoU (20 clones), and (iii) host genes induced in an ExoU-independent but type III secretion dependent manner (3 clones). In particular, ExoU was essential for the expression of immediate-early response genes, including the transcription factor c-Fos. ExoU-dependent gene expression was mediated in part by early and transient activation of the AP1 transcription factor complex. In conclusion, the present study provides a detailed insight into the response of epithelial cells to infection and indicates the significant role played by the type III virulence mechanism in the initial host response.

Pseudomonas aeruginosa activates Cl- channels in host epithelial cells

Exposure to Pseudomonas aeruginosa triggers the apoptotic cell death of Chang epithelial cells, and this depends on the expression of both the CD95 receptor and CD95 ligand. In lymphocytes CD95-mediated apoptosis is paralleled by the activation of outwardly rectifying Cl- channels. The present study was performed to explore whether P. aeruginosa-induced apoptosis of Chang epithelial cells is paralleled by activation of Cl- channels. According to whole-cell patch-clamp recordings, exposure of Chang epithelial cells to P. aeruginosa does lead to rapid activation of an outwardly rectifying Cl- -selective current. The current is inhibited by the Cl- channel blocker NPPB. Exposure of Chang epithelial cells to P. aeruginosa led to a significant decrease of cell membrane capacitance by 6%, pointing to a decrease in cell volume by 7%. Exposure to P. aeruginosa depolarized the mitochondrial membrane potential indicating apoptotic cell death. The decline of mitochondrial membrane potential was not significantly affected by NPPB. In conclusion, P. aeruginosa-induced apoptosis of Chang epithelial cells is paralleled by activation of Cl- channels. Activation of the channels participates in the alteration of cell volume but is not a prerequisite for P. aeruginosa-induced apoptosis.

Pseudomonas aeruginosa slime glycolipoprotein is a potent stimulant of tumor necrosis factor alpha gene expression and activation of transcription activators nuclear factor kappa B and activator protein 1 in human monocytes

Pseudomonas aeruginosa, an opportunistic pathogen, causes infections associated with a high incidence of morbidity and mortality in immunocompromised hosts. Production of tumor necrosis factor alpha (TNF-alpha), primarily by cells of monocytic lineage, is a crucial event in the course of these infections. During in vivo infections with P. aeruginosa, both lipopolysaccharide (LPS) and extracellular slime glycolipoprotein (GLP) produced by mucoid and nonmucoid strains are released. In the present study, we sought to explore the relative contributions of these two bacterial products to TNF-alpha production by human monocytes. To this end, fresh human monocytes and THP-1 human monocytic cells were stimulated with P. aeruginosa LPS or GLP. GLP was found to be a more potent stimulus for TNF-alpha production (threefold higher) by human monocytes than LPS. Moreover, its effect was comparable to that of viable bacteria. Quantitative mRNA analysis revealed predominantly transcriptional regulation. Electrophoretic mobility shift assays and transfection assays demonstrated activation of NF-kappa B and activator protein 1 (AP-1). NF-kappa B activation by GLP was rapid and followed the same time course as that by viable bacteria, suggesting that bacteria could directly activate NF-kappa B through GLP. Moreover P. aeruginosa GLP induced the formation of AP-1 complex with delayed kinetics compared with NF-kappa B but much more efficiently than the homologous LPS. These results identify GLP as the most important stimulant for TNF-alpha production by human monocytes. Activation of NF-kappa B and AP-1 by P. aeruginosa GLP may be involved not only in TNF-alpha induction but also in many of the inflammatory responses triggered in the course of infection with P. aeruginosa.

Necrotizing stomatitis: report of 3 Pseudomonas aeruginosa-positive patients

Necrotizing oral lesions have been described in immunosuppressed patients, usually in association with gingival and periodontal pathoses. The etiology of these lesions has not been completely elucidated. We present 3 patients with a type of necrotizing stomatitis in which clinical patterns appear distinct from the periodontal forms of the disease. The lesions yielded bacterial cultures positive for Pseudomonas aeruginosa and reverted to no growth in 2 patients after proper antibiotic therapy. We propose that P aeruginosa may be responsible for selected necrotizing oral lesions with a clinical presentation lacking typical necrotizing periodontal disease and that this condition may represent the intraoral counterpart of ecthyma gangrenosum. In such cases, bacterial culture of the lesion becomes imperative because the disease does not respond to typical periodontal and antimicrobial therapy.

Metalloproteases from Pseudomonas aeruginosa degrade human RANTES, MCP-1, and ENA-78

The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic human pathogen associated with both an acute lung disease in patients with hospital-acquired pneumonia and a chronic, progressive lung disease in individuals with cystic fibrosis. A unique characteristic of this bacterium in its natural environment is the secretion of a wide variety of factors designed to ensure its growth and survival. Evidence suggests, however, that when present in the human host, these same factors may contribute to disease. In the course of studying the effect of P. aeruginosa secretory factors on airway epithelial cells, we observed that metalloproteases in bacterial-conditioned medium, as well as purified alkaline protease and elastase, degraded human RANTES, monocyte chemotactic protein-1 (MCP-1), and epithelial neutrophil-activating protein-78 (ENA-78). Under identical conditions, interleukin-8 (IL-8) was significantly more resistant to proteolysis. Degradation was accompanied by a loss of chemotactic activity. These data suggest that metalloproteases from P. aeruginosa could alter the relative amounts of critical immunomodulatory cytokines in the airway and, thus, could contribute to the pathophysiology observed in P. aeruginosa-associated lung disease.

Apoptotic response of Chang cells to infection with Pseudomonas aeruginosa strains PAK and PAO-I: molecular ordering of the apoptosis signaling cascade and role of type IV pili

Pseudomonas aeruginosa is a gram-negative facultative opportunistic pathogen associated with severe infections in immunocompromised hosts and in patients with cystic fibrosis. P. aeruginosa strains show divergent pathogenicity in vivo and trigger apoptosis of and/or are internalized into human host cells. In the present study, we studied the molecular ordering of apoptosis signaling upon infection of human conjunctiva epithelial Chang cells with P. aeruginosa PAK as well as the role of bacterial pili in the response to the infection. Our results show that CD95 up-regulation is followed by early activation of caspase-8 and -3 and cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase. The data also demonstrate release of apoptosis inducing factor into the cytosol of infected cells. Induction of mitochondrial alterations, i.e., mitochondrial depolarization and release of cytochrome c, as well as cleavage of caspase-9, -7, and -1 occurred only at later time points. In addition, our results demonstrate that pili are required for P. aeruginosa-induced apoptosis of human epithelial cells. While the two piliated P. aeruginosa strains, PAO-I and PAK, induced apoptosis of Chang cells within 3 h of infection, the pilus-deficient P. aeruginosa mutants PAK Delta pilA and PAK Delta pilA Delta all were without effect. The pilus-deficient mutants failed to induce a significant up-regulation of CD95 on the cell surface and to trigger mitochondrial alterations or activation of caspase-8, -3, and -7. In addition, only the piliated wild-type strains induced caspase-1-mediated activation of interleukin-1 beta. Thus, pili are necessary for distinct infection-induced cellular responses of human epithelial cells.

Role and regulation of CXC-chemokines in acute experimental keratitis

The aim of this study was to elucidate the expression of chemokines, their role and regulation in bacterial corneal infection using three bacterial strains (Pseudomonas. aeruginosa- invasive, cytotoxic and contact lens induced acute red eye strains) which have been shown to produce three distinct patterns of corneal disease in the mouse. The predominant chemokine expressed in response to all three strains was MIP-2. Prolonged expression of high levels of MIP-2 was associated with increased severity of corneal inflammation. Significantly reduced disease severity upon administration of anti-MIP-2 antibodies suggested that MIP-2 may play an important role in the pathogenesis of Pseudomonas keratitis at least in part by being a major chemoattractant for polymorphonuclear leukocytes (PMN) recruitment. Interestingly, the numbers of bacteria in eyes with neutralized MIP-2 activity did not decrease even though the severity of the disease was decreased. This implies PMNs as the major destructive factor in microbial keratitis. Further, neutralization of IL-1beta activity alone using monoclonal antibodies resulted in significant reduction of both MIP-2 and KC activity indicating that chemokine levels were regulated by IL-1beta. These studies demonstrate that the regulation of MIP-2 activity may be beneficial in reducing corneal damage during microbial keratitis in rodents and perhaps that regulation of the human homologue of MIP-2, IL-8, may be useful for controlling keratitis in humans.

Pseudomonas fluorescens encodes the Crohn's disease-associated I2 sequence and T-cell superantigen

Commensal bacteria have emerged as an important disease factor in human Crohn's disease (CD) and murine inflammatory bowel disease (IBD) models. We recently isolated I2, a novel gene segment of microbial origin that is associated with human CD and that encodes a T-cell superantigen. To identify the I2 microorganism, BLAST analysis was used to identify a microbial homologue, PA2885, a novel open reading frame (ORF) in the Pseudomonas aeruginosa genome. PCR and Southern analysis identified Pseudomonas fluorescens as the originating species of I2, with homologues detectable in 3 of 13 other Pseudomonas species. Genomic cloning disclosed a locus containing the full-length I2 gene (pfiT) and three other orthologous genes, including a homologue of the pbrA/pvdS iron response gene. CD4(+) T-cell responses to recombinant proteins were potent for I2 and pfiT, but modest for PA2885. pfiT has several features of a virulence factor: association with an iron-response locus, restricted species distribution, and T-cell superantigen bioactivity. These findings suggest roles for pfiT and P. fluorescens in the pathogenesis of Crohn's disease.

Balance of pro- and anti-inflammatory cytokines correlates with outcome of acute experimental Pseudomonas aeruginosa keratitis

The purpose of this study was to elucidate the expression of pro- and anti-inflammatory cytokines in mouse corneas infected with Pseudomonas aeruginosa. Three bacterial strains (invasive, cytotoxic, or CLARE [contact lens-induced acute red eye]) which have recently been shown to produce distinct patterns of corneal disease in the mouse were used. The left mouse (BALB/c) corneas were scarified and infected with 2 x 10(6) CFU of one of the three P. aeruginosa strains, while right eyes served as controls. Animals were examined at 1, 4, 8, 16, and 24 h with a slit lamp biomicroscope to grade the severity of infection. Following examination, eyes were collected and processed for histopathology, multiprobe RNase protection assay for cytokine mRNA, enzyme-linked immunosorbent assay to quantitate cytokine proteins, and myeloperoxidase activity to quantitate polymorphonuclear leukocytes. The kinetics of appearance and magnitude of expression of key cytokines varied significantly in the three different phenotypes of P. aeruginosa infection. The predominant cytokines expressed in response to all three phenotypes were interleukin-1 beta (IL-1 beta), IL-1Ra, and IL-6. In response to the invasive strain, which induced severe corneal inflammation, significantly lower ratios of IL-1Ra to IL-1 beta were present at all time points, whereas corneas challenged with the CLARE strain, which induced very mild inflammation, showed a high ratio of IL-1Ra to IL-1 beta. The outcome of infection in bacterial keratitis correlated with the relative induction of these pro- and anti-inflammatory cytokines, and exogenous administration of recombinant rIL-1Ra (rIL-1Ra) was able to reduce the disease severity significantly. These findings point to the therapeutic potential of rIL-1Ra protein in possible treatment strategies for bacterial keratitis.

Persistent and aggressive bacteria in the lungs of cystic fibrosis children

There have been enormous improvements in life expectancy of patients with cystic fibrosis, especially with improved nutrition and better understanding of the basic cellular defects. However, infection in particular with Pseudomonas aeruginosa and Burkholderia cepacia, has the greatest effect in decreasing life expectancy. Although infections can be prevented by rigorous infection control procedures, early aggressive antimicrobial chemotherapy and established infection managed by antibiotics, they are not completely effective. A greater understanding of how the bacteria evade the host defences and produce infection is needed.

Molecular machinations: chemokine signals in host-pathogen interactions

Chemokines and their G-protein-coupled receptors represent an ancient and complex system of cellular communication participating in growth, development, homeostasis and immunity. Chemokine production has been detected in virtually every microbial infection examined; however, the precise role of chemokines is still far from clear. In most cases they appear to promote host resistance by mobilizing leukocytes and activating immune functions that kill, expel, or sequester pathogens. In other cases, the chemokine system has been pirated by pathogens, especially protozoa and viruses, which have exploited host chemokine receptors as modes of cellular invasion or developed chemokine mimics and binding proteins that act as antagonists or inappropriate agonists. Understanding microbial mechanisms of chemokine evasion will potentially lead to novel antimicrobial and anti-inflammatory therapeutic agents.