LPS-binding protein-deficient mice have an impaired defense against Gram-negative but not Gram-positive pneumonia
Judith Branger1,2,
Sandrine Florquin3,
Sylvia Knapp1,
Jaklien C. Leemans1,3,
Jennie M. Pater1,
Peter Speelman2,
Douglas T. Golenbock4 and
Tom van der Poll1,2
1 Department of Experimental Internal Medicine, 2 Department of Internal Medicine, Division of Infectious Diseases, Tropical Medicine and AIDS and 3 Department of Pathology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
4 Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, Worcester, MA, USA
Correspondence to: J. Branger; E-mail: j.branger{at}amc.uva.nl
 |
Abstract
|
---|
LPS-binding protein (LBP) can facilitate the transfer of cell wall components of both Gram-negative bacteria (LPS) and Gram-positive bacteria (lipoteichoic acid) to inflammatory cells. Although LBP is predominantly produced in the liver, recent studies have indicated that this protein is also synthesized locally in the lung by epithelial cells. To determine the role of LBP in the immune response to pneumonia, LBP gene-deficient (/) and normal wild-type (WT) mice were intra-nasally infected with either Streptococcus pneumoniae or Klebsiella pneumoniae, common Gram-positive and Gram-negative pathogens, respectively. Pneumococcal pneumonia was associated with a 7-fold rise in LBP concentrations in bronchoalveolar lavage fluid of WT mice; LBP/ mice infected with S. pneumoniae showed a similar survival and a similar bacterial burden in their lungs 48 h post-infection. In Klebsiella pneumonia, however, LBP/ mice demonstrated a diminished survival together with an enhanced bacterial outgrowth in their lungs. These data suggest that LBP is important for a protective immune response in Klebsiella pneumonia, but does not contribute to an effective host response in pneumococcal pneumonia.
Keywords: inflammation, innate immunity, LBP, mouse, pulmonary infection
 |
Introduction
|
---|
LPS-binding protein (LBP) is an acute-phase protein that binds and disaggregates LPS from Gram-negative bacteria, and facilitates the presentation of LPS monomers to the pattern recognition receptor CD14 on immunocompetent cells (1, 2). After binding of the LBPLPS complex to CD14, intracellular activation proceeds via Toll-like receptor 4 (TLR4) by a mechanism that requires an additional extracellular protein, MD-2 (35). In the absence of LBP, animals demonstrate a markedly diminished responsiveness to LPS. Indeed, rabbits or mice treated with anti-LBP antibodies and LBP gene-deficient (LBP/) mice were protected against LPS-induced lethality in association with inhibition of systemic tumor necrosis factor (TNF) release (69). Evidence exists that the absence of a strong and rapid inflammatory response to LPS makes LBP/ mice more susceptible to at least some intra-peritoneal and intravenous Gram-negative infections. LBP/ mice were unable to clear low doses of Salmonella typhimurium (912), resulting in increased lethality when compared with normal LBP+/+ wild-type (WT) mice. Furthermore, mice pre-treated with a neutralizing mAb to LBP died from overwhelming infection within 24 h after intravenous injection of a low dose of a virulent Klebsiella pneumoniae strain (13). However, anti-LBP treatment did not influence lethality induced by a higher intravenous inoculum of the same Klebsiella strain and did not affect outcome following injection with a low or high dose of an avirulent Escherichia coli strain (13).
Gram-positive bacteria do not contain LPS in their bacterial cell wall. Important pro-inflammatory cell wall components of Gram-positive bacteria are lipoteichoic acid (LTA) and peptidoglycan (PGN) (14, 15). Like LPS, these Gram-positive bacterial antigens are recognized by CD14 (1621), and their presentation to CD14 can be enhanced by LBP (2225). Knowledge of the role of LBP in immune stimulation by Gram-positive bacteria in vivo is limited. One study has reported an unaltered influx of neutrophils into the peritoneal cavity after intra-peritoneal administration of Staphylococcus aureus (12). In contrast, another recent study reported a diminished influx of leukocytes into the cerebrospinal fluid (CSF) in pneumococcal meningitis in LBP-deficient mice (26).
Pneumonia is a common and serious illness and is the leading cause of death due to infectious diseases in the United States (27). Common respiratory pathogens include the Gram-negative bacterium K. pneumoniae and the Gram-positive bacterium Streptococcus pneumoniae. Whereas K. pneumoniae is a causative organism in both community-acquired and nosocomial pneumonia, S. pneumoniae is the most commonly isolated pathogen in patients with community-acquired pneumonia (28, 29). Little is known about the role of LBP in anti-bacterial defense in the pulmonary compartment in vivo. Several lines of evidence indicate that LBP may be involved in the induction of an innate immune response in the lung during pneumonia. LBP is a product of alveolar epithelial cells of which the release is regulated by pro-inflammatory cytokines (30), and LBP can enhance the responsiveness of alveolar macrophages to LPS (31). In addition, LBP concentrations were elevated in bronchoalveolar lavage fluid (BALF) of patients with acute lung injury or allergic lung inflammation (32, 33), suggesting that LBP behaves as an acute-phase protein in the lung. Therefore, in the present study we sought to determine the role of LBP in the host response to Gram-negative and Gram-positive pneumonia. For this purpose, LBP/ and LBP+/+ WT mice were intra-nasally inoculated with either S. pneumoniae or K. pneumoniae, and the course of the infections was followed by monitoring survival, bacterial outgrowth and host inflammatory responses.
 |
Methods
|
---|
Animals
LBP/ mice, back-crossed 11 times to a C57Bl/6 background, were generated as described previously (34). Normal LBP+/+ C57Bl/6 WT mice were purchased from Harlan Sprague Dawley Inc. (Horst, The Netherlands). Male mice, aged 89 weeks, were used. All experiments were approved by the Animal Care and Use Committee of the University of Amsterdam (Amsterdam, The Netherlands).
Induction of pneumonia
Pneumonia was induced as described before (3537). Streptococcus pneumoniae serotype 3 [American Type Tissue Collection, Rockville, MD (ATCC) 6303] was used for Gram-positive infection. Pneumococci were cultured for 16 h at 37°C in 5% CO2 in ToddHewitt broth (Difco, Detroit, MI, USA). This suspension was diluted 1:100 in fresh medium and grown for 5 h to mid-logarithmic phase. Klebsiella pneumoniae serotype 2 (ATCC 43816) was used for Gram-negative infection. Klebsiella bacteria were cultured for 16 h at 37°C in 5% CO2 in tryptic soy broth (Difco). This suspension was diluted 1:100 in fresh medium and grown for 3 h to mid-logarithmic phase. Streptococcus pneumoniae and K. pneumoniae were harvested by centrifugation at 1500 g for 15 min and washed twice in sterile 0.9% saline. Bacteria were re-suspended in saline at different concentrations, as determined by plating 10-fold dilutions of the suspensions on blood agar plates. After preparation of the bacterial inocula, mice were lightly anesthetized by inhalation of isoflurane (Upjohn, Ede, The Netherlands) and 50 µl of the bacterial suspension [containing 105 colony-forming units (CFU) S. pneumoniae or 103 CFU K. pneumoniae] was inoculated intra-nasally. Control mice received 50 µl of saline.
LBP measurement
LBP concentrations in plasma and BALF of WT mice were measured. EDTA-anticoagulated blood was spun at 1000 g at 4°C for 10 min, after which plasma was stored at 20°C until further use. For bronchoalveolar lavage (BAL), the trachea was exposed through a midline incision and cannulated with a sterile 22-gauge Abbocath-T catheter (Abbott, Sligo, Ireland). BAL was performed by instilling two 0.5-ml aliquots of sterile isotonic saline. A total of 0.91.0 ml of lavage fluid was retrieved per mouse. BALF was spun at 250 g at 4°C for 10 min; the supernatant was frozen at 20°C until further use. LBP was measured by ELISA according to the manufacturer's instructions (HyCult Biotechnology B.V., Uden, The Netherlands).
Determination of bacterial outgrowth
At 6, 24 or 48 h after infection, mice were anesthetized by administering 7.0 ml kg1 of a mixture of 0.079 mg ml1 fentanyl citrate, 2.5 mg ml1 fluanisone and 1.25 mg ml1 midazolam in H2O intra-peritoneally, and sacrificed by bleeding out the vena cava inferior. Blood was collected in EDTA-containing microtubes (Becton Dickinson, Meylan, France). Both lungs were harvested, and the right lung was homogenized at 4°C in four volumes of sterile saline using a tissue homogenizer (Biospec Products, Bartlesville, OK, USA). Serial 10-fold dilutions were made in sterile saline and 10-µl volumes were plated on blood agar plates. In addition, 20-µl volumes of blood were plated. Plates were incubated at 37°C in 5% CO2, and CFU were counted after 16 h.
Cell counts in the lungs
In the same experiment, pulmonary cell suspensions were obtained from the left lung using an automated disaggregation device (Medimachine-system, Dako, Glostrup, Denmark) as described (38). After erythrocytes had been lysed with ice-cold isotonic NH4Cl solution (155 mM NH4Cl, 10 mM KHCO3, 100 mM EDTA, pH 7.4), pulmonary cells were suspended in RPMI medium (BioWhittaker, Verviers, Belgium). Total cell numbers in each sample were counted using a hemacytometer (Beckmann Coulter, Fullerton, CA, USA). Granulocyte counts in the cell suspensions were assessed using cytospin preparations stained with a modified Giemsa stain (Diff-Quick, Baxter, McGraw Park, IL, USA).
Cytokine and chemokine measurements
For cytokine measurements, lung homogenates were diluted 1:2 in lysis buffer (150 mM NaCl, 15 mM Tris, 1 mM MgCl2·H2O, 1 mM CaCl2, 1% Triton X-100, 100 µg ml1 pepstatin A, leupeptin and aprotinin, pH 7.4) and incubated at 4°C for 30 min. Homogenates were centrifuged at 1500 g for 15 min after which the supernatants were stored at 20°C until further use. Cytokine and chemokine levels in lung homogenates were measured by ELISA according to the manufacturer's instructions: TNF
, IL-6, macrophage inflammatory protein-2 (MIP-2) and keratinocyte (KC) assay kits were all obtained from R&D (Minneapolis, MN, USA).
Histologic examination
Lungs for histologic examination were harvested at 24 h (K. pneumoniae pneumonia) and 48 h (S. pneumoniae pneumonia) after inoculation, fixed in 10% formalin and embedded in paraffin. Four-micrometer sections were stained with hematoxylin and eosin, and analyzed by a pathologist who was blinded to groups.
Statistical analysis
All data are expressed as mean ± SEM. Differences between groups were analyzed by MannWhitney U test. Survival studies were analyzed using KaplanMeier curves. P < 0.05 was considered to represent a statistically significant difference.
 |
Results
|
---|
LBP concentrations
To obtain insight into local LBP concentrations in the bronchoalveolar compartment, we measured LBP protein levels in BALF of uninfected mice and mice with respiratory tract infection with either S. pneumoniae or K. pneumoniae (Fig. 1). LBP was detected at levels of 1553 ng ml1 in BALF of uninfected mice. Pneumococcal pneumonia was associated with a significant 7-fold increase in BALF LBP levels relative to controls, as measured 48 h after infection (P < 0.05 versus controls). Klebsiella pneumonia resulted in a more modest 2-fold rise in BALF LBP levels (non-significant versus controls). As expected, LBP was not detectable in BALF or plasma obtained from LBP/ mice.

View larger version (6K):
[in this window]
[in a new window]
|
Fig. 1. Bronchoalveolar LBP concentrations. LBP levels in BALF obtained from uninfected WT mice (A), and from mice 48 h after intra-nasal infection with S. pneumoniae (B) or 24 h after infection with K. pneumoniae (C). Data are mean ± SEM (610 mice per group). *P < 0.05 versus control.
|
|
Survival
In Gram-positive pneumonia induced by S. pneumoniae, survival did not differ between LBP/ and WT mice (Fig. 2A). In contrast, in Gram-negative pneumonia, survival was significantly impaired in LBP/ mice compared with WT mice (P < 0.05). All LBP/ mice died within 3 days while 37.5% of the WT mice were permanent survivors (Fig. 2B). These data suggest that LBP is important for protection against mortality induced by K. pneumoniae, while LBP does not seem to be of importance in pneumococcal pneumonia.

View larger version (11K):
[in this window]
[in a new window]
|
Fig. 2. LBP deficiency does not influence the outcome of pneumococcal pneumonia but results in an increased lethality during Klebsiella pneumonia. Survival in LBP/ and WT mice after intra-nasal inoculation with 105 CFU S. pneumoniae (A) or 103 CFU K. pneumoniae (B). N = 812 mice per group. P value indicates the difference between groups.
|
|
Bacterial outgrowth
To obtain more insight into the role of LBP in early host defense against Gram-positive and Gram-negative pneumonia, bacterial outgrowth in the lungs of LBP/ and WT mice was compared. After infection with S. pneumoniae, bacteria were counted at 24 and 48 h. At 24 h post-infection, LBP/ lungs contained slightly but significantly less CFU compared with WT lungs (P < 0.05). This difference, however, had disappeared at 48 h (Fig. 3A). The percentage of positive blood cultures in LBP/ and WT mice was similar, i.e. 57 and 63% at 24 h, and 57 and 75% at 48 h, respectively.

View larger version (14K):
[in this window]
[in a new window]
|
Fig. 3. LBP deficiency results in an enhanced outgrowth of K. pneumoniae. Bacterial outgrowth in lungs in LBP/ and WT mice at 24 and 48 h after intra-nasal inoculation with 105 CFU S. pneumoniae (A) and at 6 and 24 h after intra-nasal inoculation with 103 CFU K. pneumoniae (B). Data are mean ± SEM of 78 mice. *P < 0.05 versus WT mice.
|
|
In Gram-negative pneumonia, the bacterial load in the lungs was assessed 6 and 24 h after inoculation with K. pneumoniae. Time points earlier than those in the pneumococcal model were chosen considering the early mortality of LBP/ mice during Klebsiella pneumonia. Although bacterial counts were similar in both mouse strains at the 6-h time point, LBP/ mouse lungs contained 3 logs more bacteria at the 24-h time point compared with WT mice (P < 0.05; Fig. 3B). In Klebsiella pneumonia, at 6 h, all blood cultures were negative, whereas at 24 h, blood cultures were positive in the majority of mice (88% of LBP/ mice and 63% of WT mice). Of note, blood derived from LBP/ mice contained
2 logs more bacteria than blood from WT mice (data not shown). This finding is in concordance with the bacterial outgrowth in the lungs at the same time point.
Granulocyte influx in the lungs
The rapid influx of granulocytes to the site of infection is an important characteristic of the innate immune response during pneumonia (39). We therefore determined granulocyte numbers in whole-lung cell suspensions at 6, 24 and 48 h after induction of respiratory tract infection. In S. pneumoniae pneumonia, LBP/ mouse lungs contained similar numbers of granulocytes compared with WT mouse lungs at both 24 and 48 h post-inoculation (Table 1). Likewise, in pneumonia induced by K. pneumoniae, no difference in granulocyte counts in lungs of LBP/ and WT mice was seen after either 6 or 24 h (Table 1).
Cytokine and chemokine response to pneumonia
In pulmonary infections, local cytokine and chemokine production is an important factor in the host immune response (39, 40). We determined the influence of LBP on pulmonary cytokine concentrations during pneumococcal and Klebsiella pneumonia. Cytokine (TNF
, IL-6) and chemokine (MIP-2, KC) levels in lung homogenates measured 24 and 48 h after induction of pneumococcal pneumonia did not differ between LBP/ and WT mice (data not shown). In K. pneumoniae infection, TNF
, IL-6, MIP-2 and KC concentrations were similar in LBP/ and WT mice 6 h after infection (data not shown). In contrast, after 24 h, all cytokine and chemokine levels measured were significantly elevated in LBP/ mice compared with WT mice (P < 0.05; Table 2).
Histopathology
At 48 h after induction of S. pneumoniae infection, lungs of both WT (Fig. 4A) and LBP/ (Fig. 4B) mice displayed dense granulocytic infiltrates around vessels, edema, endothelialitis and pleuritis. The distribution and intensity of the inflammatory infiltrates were comparable in WT and LBP/ mice.

View larger version (163K):
[in this window]
[in a new window]
|
Fig. 4. Histopathology. Representative histology of lungs 48 h after S. pneumoniae infection in WT (A) and LBP/ (B) mice, and 24 h after K. pneumoniae infection in WT (C) and LBP/ (D) mice showing no significant difference. Data are representative of 6 mice per group, hematoxylin and eosin staining, magnification x10.
|
|
Infection with K. pneumoniae was characterized by a predominantly interstitial inflammation in the lungs as shown in Fig. 4(C and D) at 24 h after inoculation. No significant difference could be detected between WT (Fig. 4C) and LBP/ (Fig. 4D) mice.
 |
Discussion
|
---|
LBP has been implicated to play an important role in the host immune response against Gram-negative infections by enhancing the presentation of LPS to the pattern recognition receptor CD14 on immunocompetent cells (1, 2, 9, 13). The presentation of components of Gram-positive bacteria such as LTA and PGN to CD14 is also facilitated by LBP (2226). To determine the relevance of LBP in inducing an innate host response to pulmonary infection, we induced pneumonia caused by two common respiratory pathogens (Gram-positive, S. pneumoniae, and Gram-negative, K. pneumoniae) in LBP/ and WT mice. The outcome of S. pneumoniae pneumonia was not influenced by the absence of LBP, as reflected by similar survival curves and similar bacterial outgrowth after 48 h in LBP/ and WT mice. In contrast, in K. pneumoniae pneumonia, the protective role of LBP was evident as shown by an increased mortality rate and an increased number of bacteria in lungs of LBP/ mice compared with WT mice.
Evidence indicates that LBP can be produced not only in the liver, but also in a variety of tissues including the lungs (30, 31, 4143). Elevated levels of LBP in BALF of patients with acute respiratory distress syndrome and in BALF of asthma patients after allergen challenge (3133) suggest that local production of LBP may contribute to host defense against bacterial challenges in the lung. We here demonstrate that mice have detectable LBP concentrations in their BALF, which increase upon bacterial respiratory tract infection, in particular during pneumococcal pneumonia.
During bacterial growth and death, large amounts of bacterial cell wall components such as LPS, LTA and PGN are released. It is known that LBP can bind to these components. Moreover, in vitro studies have shown that LBP can also opsonize intact Gram-negative and -positive bacteria including S. pneumoniae (26, 44).
Several in vitro studies have attributed an important role to LBP in activating cells upon stimulation with components of Gram-positive bacteria. It was shown that TNF
production by monocytes in response to pneumococcal and staphylococcal LTA (25) and group B streptococcal (24) and pneumococcal cell walls (26) was dose dependently enhanced by the presence of LBP. LBP was also shown to play a stimulating role in the recognition and phagocytosis of the Gram-positive bacterium Bacillus subtilis by CD14-expressing CHO and U937 cells (23). Others, however, were unable to show a modulating effect of LBP on TNF
production by PBMC in response to B. subtilis and Staphylococcus aureus LTA (21). Data on the effect of LBP in cell activation induced by PGN, another important immunostimulatory component of Gram-positive bacteria, remain controversial. Binding of PGN to the CD14 receptor was enhanced by the presence of LBP in in vitro experiments (22). In two earlier reports, however, LBP failed to augment PGN-induced cell activation (45, 46). Data on the role of LBP in Gram-positive infections in vivo are limited. Weber et al. (26) showed a decreased influx of leukocytes in the CSF of LBP/ mice in a model of meningitis induced by live pneumococci and pneumococcal cell walls. However, the absence of LBP did not influence host defense as measured by similar numbers of CFU in the CSF of LBP/ and WT mice. In line with these findings, we show that the absence of LBP in a murine model of pneumococcal pneumonia does not affect innate host defense mechanisms. LBP-deficient mice were able to mount an inflammatory response comparable to WT mice as shown by similar survival curves, bacterial numbers and neutrophil influx in the pulmonary compartment as well as cytokine production and histopathology scores. At 24 h post-infection, LBP/ mice even displayed slightly less pneumococci in their lungs than WT mice. A recent study has implicated TLR4 in the early recognition of S. pneumoniae in the respiratory tract via a specific interaction with pneumolysin, a cytolytic toxin expressed by the pneumococcus (47). The current data suggest that LBP does not play a role herein.
Since its discovery in 1986 (48), LBP has been shown to be important in the induction of an inflammatory response against LPS (1, 69, 44, 49) and Gram-negative bacteria (911, 13, 50). In our experiments, LBP clearly played a protective role in K. pneumoniae pneumonia. While our studies were in progress, Fan et al. (51) reported similar data on survival and bacterial outgrowth during Klebsiella pneumonia in LBP/ mice. Of note, whereas Fan et al. showed a reduced influx of granulocytes into the pulmonary compartment of LBP/ mice, we found similar granulocyte numbers in LBP/ and WT mice. In addition, we detected a profound increase in cytokine and chemokine concentrations in lung homogenates of LBP/ mice compared with WT mice, while Fan et al. found either similar or lower cytokine and chemokine levels in LBP/ versus WT mice. In our opinion, the impressive difference in pulmonary bacterial load (3 logs) in LBP/ versus WT mice, providing a more potent pro-inflammatory stimulus, is responsible for our findings. Furthermore, a reduced capacity of phagocytes to phagocytose and kill bacteria in the absence of LBP may also play a role, since in vitro studies showed enhanced phagocytosis and killing of bacteria by alveolar macrophages in the presence of LBP (52, 53).
Although, in recent years, much has been learnt from in vitro studies involving LBP, knowledge about the function of LBP during infections in vivo is limited. In light of the clinical relevance of pulmonary infections worldwide, we considered it important to evaluate the role of LBP during Gram-positive and Gram-negative pneumonia. We conclude that LBP plays an essential role in innate immunity during pneumonia caused by K. pneumoniae but does not contribute to host defense in pneumococcal pneumonia. Further research is warranted to establish the role of LBP in the pulmonary immune response to other respiratory pathogens.
 |
Acknowledgements
|
---|
The authors thank J. Daalhuisen and I. Kop for excellent technical assistance.
 |
Abbreviations
|
---|
ATCC | American Type Tissue Collection, Rockville, MD |
BAL | bronchoalveolar lavage |
BALF | bronchoalveolar lavage fluid |
CFU | colony-forming units |
CSF | cerebrospinal fluid |
KC | keratinocyte |
LBP | LPS-binding protein |
LTA | lipoteichoic acid |
MIP-2 | macrophage inflammatory protein-2 |
PGN | peptidoglycan |
TLR4 | Toll-like receptor 4 |
TNF | tumor necrosis factor |
WT | wild type |
 |
Notes
|
---|
Transmitting editor: T. Takai
Received 19 May 2004,
accepted 20 August 2004.
 |
References
|
---|
- Wright, S. D., Ramos, R. A., Tobias, P. S., Ulevitch, R. J. and Mathison, J. C. 1990. CD14, a receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein. Science 249:1431.[ISI][Medline]
- Ulevitch, R. J. and Tobias, P. S. 1999. Recognition of gram-negative bacteria and endotoxin by the innate immune system. Curr. Opin. Immunol. 11:19.[CrossRef][ISI][Medline]
- Aderem, A. and Ulevitch, R. J. 2000. Toll-like receptors in the induction of the innate immune response. Nature 406:782.[CrossRef][ISI][Medline]
- Shimazu, R., Akashi, S., Ogata, H. et al. 1999. MD-2, a molecule that confers lipopolysaccharide responsiveness on Toll-like receptor 4. J. Exp. Med. 189:1777.[Abstract/Free Full Text]
- Hoshino, K., Takeuchi, O., Kawai, T. et al. 1999. Cutting edge: Toll-like receptor 4 (TLR4)-deficient mice are hyporesponsive to lipopolysaccharide: evidence for TLR4 as the Lps gene product. J. Immunol. 162:3749.[Abstract/Free Full Text]
- Gallay, P., Heumann, D., Le Roy, D., Barras, C. and Glauser, M. P. 1993. Lipopolysaccharide-binding protein as a major plasma protein responsible for endotoxemic shock. Proc. Natl. Acad. Sci. USA 90:9935.[Abstract]
- Gallay, P., Heumann, D., Le Roy, D., Barras, C. and Glauser, M. P. 1994. Mode of action of anti-lipopolysaccharide-binding protein antibodies for prevention of endotoxemic shock in mice. Proc. Natl. Acad. Sci. USA 91:7922.[Abstract]
- Le Roy, D., Di Padova, F., Tees, R. et al. 1999. Monoclonal antibodies to murine lipopolysaccharide (LPS)-binding protein (LBP) protect mice from lethal endotoxemia by blocking either the binding of LPS to LBP or the presentation of LPS/LBP complexes to CD14. J. Immunol. 162:7454.[Abstract/Free Full Text]
- Jack, R. S., Fan, X., Bernheiden, M. et al. 1997. Lipopolysaccharide-binding protein is required to combat a murine gram-negative bacterial infection. Nature 389:742.[CrossRef][ISI][Medline]
- Bernheiden, M., Heinrich, J. M., Minigo, G. et al. 2001. LBP, CD14, TLR4 and the murine innate immune response to a peritoneal Salmonella infection. J. Endotoxin Res. 7:447.[ISI][Medline]
- Heinrich, J. M., Bernheiden, M., Minigo, G. et al. 2001. The essential role of lipopolysaccharide-binding protein in protection of mice against a peritoneal Salmonella infection involves the rapid induction of an inflammatory response. J. Immunol. 167:1624.[Abstract/Free Full Text]
- Fierer, J., Swancutt, M. A., Heumann, D. and Golenbock, D. 2002. The role of lipopolysaccharide binding protein in resistance to Salmonella infections in mice. J. Immunol. 168:6396.[Abstract/Free Full Text]
- Le Roy, D., Di Padova, F., Adachi, Y., Glauser, M. P., Calandra, T. and Heumann, D. 2001. Critical role of lipopolysaccharide-binding protein and CD14 in immune responses against gram-negative bacteria. J. Immunol. 167:2759.[Abstract/Free Full Text]
- De Kimpe, S. J., Kengatharan, M., Thiemermann, C. and Vane, J. R. 1995. The cell wall components peptidoglycan and lipoteichoic acid from Staphylococcus aureus act in synergy to cause shock and multiple organ failure. Proc. Natl. Acad. Sci. USA 92:10359.[Abstract]
- Kengatharan, K. M., De Kimpe, S., Robson, C., Foster, S. J. and Thiemermann, C. 1998. Mechanism of gram-positive shock: identification of peptidoglycan and lipoteichoic acid moieties essential in the induction of nitric oxide synthase, shock, and multiple organ failure. J. Exp. Med. 188:305.[Abstract/Free Full Text]
- Gupta, D., Kirkland, T. N., Viriyakosol, S. and Dziarski, R. 1996. CD14 is a cell-activating receptor for bacterial peptidoglycan. J. Biol. Chem. 271:23310.[Abstract/Free Full Text]
- Pugin, J., Heumann, I. D., Tomasz, A. et al. 1994. CD14 is a pattern recognition receptor. Immunity 1:509.[ISI][Medline]
- Cleveland, M. G., Gorham, J. D., Murphy, T. L., Tuomanen, E. and Murphy, K. M. 1996. Lipoteichoic acid preparations of gram-positive bacteria induce interleukin-12 through a CD14-dependent pathway. Infect. Immun. 64:1906.[Abstract]
- Kusunoki, T., Hailman, E., Juan, T. S., Lichenstein, H. S. and Wright, S. D. 1995. Molecules from Staphylococcus aureus that bind CD14 and stimulate innate immune responses. J. Exp. Med. 182:1673.[Abstract]
- Landmann, R., Muller, B. and Zimmerli, W. 2000. CD14, new aspects of ligand and signal diversity. Microbes Infect. 2:295.[CrossRef][ISI][Medline]
- Hermann, C., Spreitzer, I., Schroder, N. W. et al. 2002. Cytokine induction by purified lipoteichoic acids from various bacterial speciesrole of LBP, sCD14, CD14 and failure to induce IL-12 and subsequent IFN-gamma release. Eur. J. Immunol. 32:541.[CrossRef][ISI][Medline]
- Dziarski, R., Tapping, R. I. and Tobias, P. S. 1998. Binding of bacterial peptidoglycan to CD14. J. Biol. Chem. 273:8680.[Abstract/Free Full Text]
- Fan, X., Stelter, F., Menzel, R. et al. 1999. Structures in Bacillus subtilis are recognized by CD14 in a lipopolysaccharide binding protein-dependent reaction. Infect. Immun. 67:2964.[Abstract/Free Full Text]
- Medvedev, A. E., Flo, T., Ingalls, R. R. et al. 1998. Involvement of CD14 and complement receptors CR3 and CR4 in nuclear factor-kappaB activation and TNF production induced by lipopolysaccharide and group B streptococcal cell walls. J. Immunol. 160:4535.[Abstract/Free Full Text]
- Schroder, N. W., Morath, S., Alexander, C. et al. 2003. Lipoteichoic acid (LTA) of Streptococcus pneumoniae and Staphylococcus aureus activates immune cells via Toll-like receptor (TLR)-2, lipopolysaccharide-binding protein (LBP), and CD14, whereas TLR-4 and MD-2 are not involved. J. Biol. Chem. 278:15587.[Abstract/Free Full Text]
- Weber, J. R., Freyer, D., Alexander, C. et al. 2003. Recognition of pneumococcal peptidoglycan: an expanded, pivotal role for LPS binding protein. Immunity 19:269.[CrossRef][ISI][Medline]
- Pinner, R. W., Teutsch, S. M., Simonsen, L. et al. 1996. Trends in infectious diseases mortality in the United States. J. Am. Med. Assoc. 275:189.[Abstract]
- Bartlett, J. G. and Mundy, L. M. 1995. Community-acquired pneumonia. N. Engl. J. Med. 333:1618.[Free Full Text]
- Brown, P. D. and Lerner, S. A. 1998. Community-acquired pneumonia. Lancet 352:1295.[CrossRef][ISI][Medline]
- Dentener, M. A., Vreugdenhil, A. C., Hoet, P. H. et al. 2000. Production of the acute-phase protein lipopolysaccharide-binding protein by respiratory type II epithelial cells: implications for local defense to bacterial endotoxins. Am. J. Respir. Cell Mol. Biol. 23:146.[Abstract/Free Full Text]
- Martin, T. R., Mathison, J. C., Tobias, P. S. et al. 1992. Lipopolysaccharide binding protein enhances the responsiveness of alveolar macrophages to bacterial lipopolysaccharide. Implications for cytokine production in normal and injured lungs. J. Clin. Investig. 90:2209.[ISI][Medline]
- Martin, T. R., Rubenfeld, G. D., Ruzinski, J. T. et al. 1997. Relationship between soluble CD14, lipopolysaccharide binding protein, and the alveolar inflammatory response in patients with acute respiratory distress syndrome. Am. J. Respir. Crit. Care Med. 155:937.[Abstract]
- Dubin, W., Martin, T. R., Swoveland, P. et al. 1996. Asthma and endotoxin: lipopolysaccharide-binding protein and soluble CD14 in bronchoalveolar compartment. Am. J. Physiol. 270:L736.[ISI][Medline]
- Wurfel, M. M., Monks, B. G., Ingalls, R. R. et al. 1997. Targeted deletion of the lipopolysaccharide (LPS)-binding protein gene leads to profound suppression of LPS responses ex vivo, whereas in vivo responses remain intact. J. Exp. Med. 186:2051.[Abstract/Free Full Text]
- Lauw, F. N., Branger, J., Florquin, S. et al. 2002. IL-18 improves the early antimicrobial host response to pneumococcal pneumonia. J. Immunol. 168:372.[Abstract/Free Full Text]
- Rijneveld, A. W., Weijer, S., Florquin, S. et al. 2004. Thrombomodulin mutant mice with a strongly reduced capacity to generate activated protein C have an unaltered pulmonary immune response to respiratory pathogens and lipopolysaccharide. Blood 103:1702.[Abstract/Free Full Text]
- Rijneveld, A. W., Lauw, F. N., Schultz, M. J. et al. 2002. The role of interferon-gamma in murine pneumococcal pneumonia. J. Infect. Dis. 185:91.[CrossRef][ISI][Medline]
- Leemans, J. C., Juffermans, N. P., Florquin, S. et al. 2001. Depletion of alveolar macrophages exerts protective effects in pulmonary tuberculosis in mice. J. Immunol. 166:4604.[Abstract/Free Full Text]
- Zhang, P., Summer, W. R., Bagby, G. J. and Nelson, S. 2000. Innate immunity and pulmonary host defense. Immunol. Rev. 173:39.[CrossRef][ISI][Medline]
- Strieter, R. M., Belperio, J. A. and Keane, M. P. 2002. Cytokines in innate host defense in the lung. J. Clin. Investig. 109:699.[Free Full Text]
- Lee, P. T., Holt, P. G. and McWilliam, A. S. 2000. Role of alveolar macrophages in innate immunity in neonates. Evidence for selective lipopolysaccharide binding protein production by rat neonatal alveolar macrophages. Am. J. Respir. Cell Mol. Biol. 23:652.[Abstract/Free Full Text]
- Wang, S. C., Klein, R. D., Wahl, W. L. et al. 1998. Tissue coexpression of LBP and CD14 mRNA in a mouse model of sepsis. J. Surg. Res. 76:67.[CrossRef][ISI][Medline]
- Su, G., Freeswick, P., Geller, D. et al. 1994. Molecular cloning, characterization, and tissue distribution of rat lipopolysaccharide binding protein. Evidence for extrahepatic expression. J. Immunol. 153:743.[Abstract/Free Full Text]
- Schumann, R. R., Leong, S. R., Flaggs, G. W. et al. 1990. Structure and function of lipopolysaccharide binding protein. Science 249:1429.[ISI][Medline]
- Mathison, J. C., Tobias, P. S., Wolfson, E. and Ulevitch, R. J. 1992. Plasma lipopolysaccharide (LPS)-binding protein. A key component in macrophage recognition of gram-negative LPS. J. Immunol. 149:200.[Abstract/Free Full Text]
- Weidemann, B., Brade, H., Rietschel, E. T. et al. 1994. Soluble peptidoglycan-induced monokine production can be blocked by anti-CD14 monoclonal antibodies and by lipid A partial structures. Infect. Immun. 62:4709.[Abstract]
- Malley, R., Henneke, P., Morse, S. C. et al. 2003. Recognition of pneumolysin by Toll-like receptor 4 confers resistance to pneumococcal infection. Proc. Natl. Acad. Sci. USA 100:1966.[Abstract/Free Full Text]
- Tobias, P. S., Soldau, K. and Ulevitch, R. J. 1986. Isolation of a lipopolysaccharide-binding acute phase reactant from rabbit serum. J. Exp. Med. 164:777.[Abstract]
- Tobias, P. S. and Ulevitch, R. J. 1993. Lipopolysaccharide binding protein and CD14 in LPS dependent macrophage activation. Immunobiology 187:227.[ISI][Medline]
- Yang, K. K., Dorner, B. G., Merkel, U. et al. 2002. Neutrophil influx in response to a peritoneal infection with Salmonella is delayed in lipopolysaccharide-binding protein or CD14-deficient mice. J. Immunol. 169:4475.[Abstract/Free Full Text]
- Fan, M. H., Klein, R. D., Steinstraesser, L. et al. 2002. An essential role for lipopolysaccharide-binding protein in pulmonary innate immune responses. Shock 18:248.[CrossRef][ISI][Medline]
- Klein, R. D., Su, G. L., Schmidt, C. et al. 2000. Lipopolysaccharide-binding protein accelerates and augments Escherichia coli phagocytosis by alveolar macrophages. J. Surg. Res. 94:159.[CrossRef][ISI][Medline]
- Wright, S., Tobias, P., Ulevitch, R. and Ramos, R. 1989. Lipopolysaccharide (LPS) binding protein opsonizes LPS-bearing particles for recognition by a novel receptor on macrophages. J. Exp. Med. 170:1231.[Abstract]