Role of Toll-like receptor 4 in gram-positive and gram-negative pneumonia in mice (original) (raw)
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Infection and Immunity, 2009
Airway epithelial cells act as the first barrier against pathogens. These cells recognize conserved structural motifs expressed by microbial pathogens via Toll-like receptors (TLRs) expressed on the surface. In contrast to the level of expression in lymphoid cells, the level of expression of TLR2 and TLR4 in airway epithelial cells is low under physiological conditions. Here we explored whether Klebsiella pneumoniae upregulates the expression of TLRs in human airway epithelial cells. We found that the expression of TLR2 and TLR4 by A549 cells and human primary airway cells was upregulated upon infection with K. pneumoniae. The increased expression of TLRs resulted in enhancement of the cellular response upon stimulation with Pam3CSK4 and lipopolysaccharide, which are TLR2 and TLR4 agonists, respectively. Klebsiella-dependent upregulation of TLR expression occurred via a positive IB␣-dependent NF-〉 pathway and via negative p38 and p44/42 mitogen-activated protein kinase-dependent pathways. We showed that Klebsiella-induced TLR2 and TLR4 upregulation was dependent on TLR activation. An isogenic capsule polysaccharide (CPS) mutant did not increase TLR2 and TLR4 expression. Purified CPS upregulated TLR2 and TLR4 expression, and polymyxin B did not abrogate CPS-induced TLR upregulation. Although no proteins were detected in the CPS preparation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and colloidal gold staining, we could not rule out the possibility that traces of protein in our CPS preparation could have been responsible, at least in part, for the TLR upregulation.
Shock, 2012
Pulmonary contusion is a major cause of respiratory failure in trauma patients. This injury frequently leads to immune suppression and infectious complications such as pneumonia. The mechanism whereby trauma leads to an immune suppressed state is poorly understood. To further study this phenomenon, we developed an animal model of pulmonary contusion complicated by pneumonia and assessed the effect of pulmonary contusion and pneumonia on toll-like receptor expression in alveolar macrophages. Using a mouse model, pulmonary contusion (PC) was induced on the right lung and pneumonia was induced with Pseudomonas aeruginosa (Pa) injected intratracheally 48 hours after injury. Susceptibility to pneumonia was assessed by mortality at seven days. Uninjured animals were used as controls. Bronchoalveolar lavage (BAL) fluid and blood were assayed 48 hours after injury and 24 hours after Pa instillation to look at markers of systemic inflammation. Toll-like receptor (TLR) expression in the initial inflammatory response was analyzed by flow cytometry. Unexpectedly, injured animals subjected to intratracheal injection of Pa at 48h after pulmonary contusion demonstrated increased survival compared to uninjured animals. BAL cytokine expression was increased significantly after Pa administration but not after PC alone. TLR4 expression on alveolar macrophages was significantly elevated in the injured group compared to sham but not in neutrophils. Animals subjected to PC are more resistant to mortality from infection with Pa and display an enhanced cytokine response when subsequently subjected to Pa. Increased expression of TLR4 on alveolar macrophages and enhanced innate immunity is a possible mechanism of increased cytokine production and decreased susceptibility to pneumonia.
Clinical and Vaccine Immunology, 2013
ABSTRACTCoinfection with bacteria is a major cause of mortality during influenza epidemics. Recently, Toll-like receptor (TLR) agonists were shown to have immunomodulatory functions. In the present study, we investigated the effectiveness and mechanisms of the new TLR4 agonistic monoclonal antibody UT12 against secondary pneumococcal pneumonia induced by coinfection with influenza virus in a mouse model. Mice were intranasally inoculated withStreptococcus pneumoniae2 days after influenza virus inoculation. UT12 was intraperitoneally administered 2 h before each inoculation. Survival rates were significantly increased and body weight loss was significantly decreased by UT12 administration. Additionally, the production of inflammatory mediators was significantly suppressed by the administration of UT12. In a histopathological study, pneumonia in UT12-treated mice was very mild compared to that in control mice. UT12 increased antimicrobial defense through the acceleration of macrophage...
Microbes and Infection, 2008
Pneumocystis pneumonia (PcP) is marked by substantial inflammatory damage to the lung. We have found that Toll-like receptor 2 (TLR2) mediates macrophage inflammatory responses to Pneumocystis and hypothesized that TLR2 deficiency would lead to less severe inflammation and milder lung injury during PcP. Histopathology examination showed that TLR2À/À mice with PcP indeed exhibited milder pulmonary inflammation. TLR2À/À mouse lungs contained less TNF-a and displayed lower levels of NF-kB activation during PcP. However, TLR2À/À mice with PcP displayed increased severity in symptoms and organism burden. The increased organism burden is likely due to defects in protective mechanisms in TLR2À/À mice. mRNA levels of the inducible nitric oxide synthase and NADPH oxidase p47phox, as well as nitric oxide levels in the lungs, were decreased in TLR2À/À PcP mice. Taken together, this study shows that TLR2-mediated inflammatory responses contribute to a certain degree to the clearance of Pneumocystis organism in mice.
Journal of Inflammation Research, 2008
Background: Toll-like receptors (TLRs) represent a conserved family of innate immune recognition receptors. Among TLRs, TLR4 is important for the recognition of Gram-negative bacteria, whereas TLR2 recognizes cell wall constituents of Gram-positive microorganisms, such as peptidoglycan (PGN). Methods: To evaluate the role of TLR4 in the pathogenesis of acute lung injury induced by Escherichia coli endotoxin (lipopolysaccharide; LPS) or PGN, we compared infl ammatory cell accumulation in bronchoalveolar lavage (BAL) fl uid and lung pathology between C3H/HeJ (TLR4 mutant) and wild-type C3H/HeN mice. The levels of proinfl ammatory cytokines and chemokines in plasma and BAL fl uid and nuclear factor-κB (NF-κB) translocation in the lung were also evaluated. Results: In C3H/HeJ mice, LPS-induced neutrophil emigration was signifi cantly decreased compared with C3H/HeN mice, whereas PGN-induced neutrophil emigration did not differ. Differential cell count in BAL fl uid revealed comparable neutrophil recruitment in the alveolar space. In TLR4 mutant mice, LPS-induced upregulation of tumor necrosis factor-alpha (TNF-α), KC, and CXCL10 in plasma and BAL fl uid was attenuate, which was not different after PGN. NF-κB translocation in the lung was signifi cantly decreased in C3H/HeJ compared with C3H/HeN mice, whereas PGN-induced NF-κB translocation was not different. Conclusion: These results suggest that TLR4 mediates infl ammatory cascade induced by Gram-negative bacteria that is locally administered.
PLoS ONE, 2011
TLR2 and TLR4 are crucial for recognition of Chlamydia pneumoniae in vivo, since infected TLR2/4 double-deficient mice are unable to control the infection as evidenced by severe loss of body weight and progressive lethal pneumonia. Unexpectedly, these mice display higher pulmonary levels of the protective cytokine IFNc than wild type mice. We show here, that antigen-specific CD4 + T-cells are responsible for the observed IFNc-secretion in vivo and their frequency is higher in TLR2/4 double-deficient than in wild type mice. The capacity of TLR2/4 double-deficient dendritic cells to re-stimulate CD4 + T-cells did not differ from wild type dendritic cells. However, the frequency of CD4 + CD25 + Foxp3 + T-cells was considerably higher in wild type compared to TLR2/4 double-deficient mice and was inversely related to the number of IFNc-secreting CD4 + effector T-cells. Despite increased IFNc-levels, at least one IFNc-mediated response, protective NOsecretion, could not be induced in the absence of TLR2 and 4. In summary, CD4 + CD25 + Foxp3 + regulatory T-cells fail to expand in the absence of TLR2 and TLR4 during pulmonary infection with C. pneumoniae, which in turn enhances the frequency of CD4 + IFNc + effector T-cells. Failure of IFNc to induce NO in TLR2/4 double-deficient cells represents one possible mechanism why TLR2/4 double-deficient mice are unable to control pneumonia caused by C. pneumoniae and succumb to the infection.
Infection and Immunity, 2009
Airway epithelial cells act as the first barrier against pathogens. These cells recognize conserved structural motifs expressed by microbial pathogens via Toll-like receptors (TLRs) expressed on the surface. In contrast to the level of expression in lymphoid cells, the level of expression of TLR2 and TLR4 in airway epithelial cells is low under physiological conditions. Here we explored whether Klebsiella pneumoniae upregulates the expression of TLRs in human airway epithelial cells. We found that the expression of TLR2 and TLR4 by A549 cells and human primary airway cells was upregulated upon infection with K. pneumoniae. The increased expression of TLRs resulted in enhancement of the cellular response upon stimulation with Pam3CSK4 and lipopolysaccharide, which are TLR2 and TLR4 agonists, respectively. Klebsiella-dependent upregulation of TLR expression occurred via a positive IB␣-dependent NF-〉 pathway and via negative p38 and p44/42 mitogen-activated protein kinase-dependent pathways. We showed that Klebsiella-induced TLR2 and TLR4 upregulation was dependent on TLR activation. An isogenic capsule polysaccharide (CPS) mutant did not increase TLR2 and TLR4 expression. Purified CPS upregulated TLR2 and TLR4 expression, and polymyxin B did not abrogate CPS-induced TLR upregulation. Although no proteins were detected in the CPS preparation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and colloidal gold staining, we could not rule out the possibility that traces of protein in our CPS preparation could have been responsible, at least in part, for the TLR upregulation.
The Journal of Infectious Diseases, 2002
Legionella pneumophila is a gram-negative microorganism that causes a severe pneumonia known as "legionnaires disease." Toll-like receptor 4 (TLR4) transduces the lipopolysaccharide signal and is therefore considered to play a role in host defense against gram-negative bacterial infection. To determine the role of TLR4 in L. pneumophila pneumonia, C3H/HeJ mice, which display a nonfunctional gene encoding TLR4 (TLR4), and wild-type (wt) C3H/HeN mice were intranasally inoculated with L. pneumophila serogroup 1. Infection proceeded in an identical way in TLR4 mutant and wt mice, as reflected by similar bacterial outgrowth in the lungs. In addition, the inflammatory responses to L. pneumophila infection-as assessed by histopathologic analysis, cell influx in bronchoalveolar lavage fluid, myeloperoxidase activity in lungs, and lung cytokine concentrations-were indistinguishable in TLR4 mutant and wt mice. These data suggest that, in this mouse model, TLR4 does not play a role in resistance to L. pneumophila.
Divergent Functions of Toll-like Receptors during Bacterial Lung Infections
American Journal of Respiratory and Critical Care Medicine, 2014
Lower respiratory tract infections caused by bacteria are a major cause of death in humans irrespective of sex, race, or geography. Indeed, accumulated data indicate greater mortality and morbidity due to these infections than cancer, malaria, or HIV infection. Successful recognition of, followed by an appropriate response to, bacterial pathogens in the lungs is crucial for effective pulmonary host defense. Although the early recruitment and activation of neutrophils in the lungs is key in the response against invading microbial pathogens, other sentinels, such as alveolar macrophages, epithelial cells, dendritic cells, and CD4 1 T cells, also contribute to the elimination of the bacterial burden. Pattern recognition receptors, such as toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors, are important for recognizing and responding to microbes during pulmonary infections. However, bacterial pathogens have acquired crafty evasive strategies to circumvent the pattern recognition receptor response and thus establish infection. Increased understanding of the function of TLRs and evasive mechanisms used by pathogens during pulmonary infection will deepen our knowledge of immunopathogenesis and is crucial for developing effective therapeutic and/or prophylactic measures. This review summarizes current knowledge of the multiple roles of TLRs in bacterial lung infections and highlights the mechanisms used by pathogens to modulate or interfere with TLR signaling in the lungs.