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*
Laboratory of Experimental Internal Medicine and Departments of
Infectious Diseases, Tropical Medicine, and AIDS and
Pathology, University of Amsterdam, Amsterdam, The Netherlands; and
Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Antibacterial host defense in the pulmonary compartment is regulated by
a complex interaction between immunocompetent cells and a network of
cytokines and chemokines (4). IL-18 is a proinflammatory
cytokine which was originally identified in mice during endotoxin shock
as a costimulatory factor for the production of IFN-
(5, 6, 7, 8). IL-18 is mainly produced by activated macrophages
and is first synthesized as a precursor protein (pro-IL-18, 24 kDa),
which requires splicing by IL-1
-converting enzyme to liberate the
18-kDa mature active protein (9, 10). Although IL-18 alone
is not a potent stimulator of IFN- production, it synergistically
enhances IL-12-induced IFN- production (11). Besides
its IFN--inducing effect, IL-18 has many proinflammatory effects on
T and NK cells, enhancing proliferation and cytotoxicity and
stimulating the production of cytokines, including TNF, IL-1, IL-2,
IL-6, and GM-CSF (11, 12, 13, 14, 15). In addition, IL-18 enhances Fas
ligand-mediated cytotoxicity of NK and T cells and possesses potent
antitumor activity (16, 17, 18).
Recent studies have investigated the role of IL-18 in the host response to infection. During experimental endotoxemia in mice, neutralization of IL-18 protected against LPS-induced liver injury and lethality (19, 20). In contrast, IL-18 was protective during infections with Yersinia enterocolitica and intracellular pathogens like Leishmania major and Salmonella typhimurium (21, 22, 23). The role of IL-18 in the pathogenesis of bacterial pneumonia is unknown. Therefore, in this study we sought to determine the importance of IL-18 in host defense against pneumonia caused by S. pneumoniae. For this purpose, we compared survival and several components of the host response in IL-18 gene-deficient (IL-18-/-) and wild-type (WT)2 mice. Considering that IL-18 and IL-12 can synergistically activate immunocompetent cells (7, 8), we also determined the role of IL-12 in the innate immune response to pneumococcal pneumonia using IL-12p40 gene-deficient (IL-12-/-) mice. Finally, the possible interaction between endogenous IL-12 and IL-18 during pneumococcal pneumonia was studied by treatment of IL-18-/- and WT mice with an anti-IL-12 Ab.
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Materials and Methods |
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All experiments were approved by the Institutional Animal Care and Use Committee of the Academic Medical Center of the University of Amsterdam. IL-18-/- mice were generated as described previously (13). IL-18-/- mice were on the C57BL/6 background. IL-12-/- BALB/c mice were purchased from The Jackson Laboratory (Bar Harbor, ME). Normal C57BL/6 and BALB/c WT mice, used as controls for IL-18-/- and IL-12-/- mice, respectively, were obtained from Harlan Sprague-Dawley (Horst, The Netherlands). Sex- and age-matched (8- to 12-wk old mice) were used in all experiments.
Induction of pneumonia
Pneumonia was induced as described before (24, 25, 26). S. pneumoniae serotype 3 was obtained from American Type Culture Collection (6303; Manassas, VA). Pneumococci were cultured for 16 h at 37°C in 5% CO2 in Todd-Hewitt broth. This suspension was diluted 1/100 in fresh medium and grown for 5 h to midlogarithmic phase. Pneumococci were harvested by centrifugation at 1500 x g for 15 min and washed twice in sterile 0.9% saline. Bacteria were resuspended in saline at different concentrations (see Results), as determined by plating 10-fold dilutions of the suspensions on blood agar plates. Mice were lightly anesthetized by inhalation of isoflurane (Upjohn, Ede, The Netherlands), and 50 µl of bacterial suspension was inoculated intranasally. Control mice received 50 µl of saline.
RT-PCR
Lungs were harvested at 24 and 48 h after inoculation with
S. pneumoniae and 24 h after inoculation with saline,
snap-frozen in liquid nitrogen, and stored at -70°C. To extract
total cellular RNA, lungs from three mice per time point were pooled
and homogenized in 1 ml of TRIzol Reagent (Life Technologies, Grand
Island, NY). Then total RNA was isolated using chloroform extraction
and isopropanol precipitation. The RNA pellet was dissolved in 100 µl
of diethylpyrocarbonate-treated water and quantified by
spectrophotometry. Reverse transcription was performed by mixing 2 µg
of total cellular RNA with 0.5 µg of oligo(dT) (Life Technologies) in
a total volume of 12 µl. The mixture was incubated at 72°C for 10
min. Thereafter, 8 µl of a solution containing 4 µl of 5x First
Strand buffer (Life Technologies), 10 mM DTT (Life Technologies), 1.25
mM dNTPs (Amersham Pharmacia Biotech, Little Chalfont, U.K.),
and 100 U of Superscript Reverse Transcriptase (Life Technologies) was
added and the mixture was incubated at 42°C for 1 h.
Finally, the tubes were heated to 72°C for 10 min after which 180
µl of H2O was added to the reaction mixture.
Samples were stored at -20°C until further use. For PCR, 5 µl of
cDNA solution was mixed with 20 µl of a solution containing 1x PCR
buffer (67 mM Tris-HCl (pH 8.8), 6.7 mM MgCl2, 10
mM 2-ME, 0.67 µg of EDTA, 16.6 mM
(NH4)2SO4,
2% DMSO (Merck, München, Germany), 1.25 µg of BSA (New England
Biolabs, Beverly, MA), 0.5 U of AmpliTaq DNA polymerase (PerkinElmer,
Branchburg, NJ), and 75 ng of sense- and antisense oligonucleotide
primers specific for IL-18 and -actin (internal standard). The PCR
were performed in a thermocycler (Gene Amp. PCR System 9700;
PerkinElmer) using the following conditions: 94°C for 5 min (1 cycle)
followed immediately by 95°C for 1 min, 58°C for 1 min, 72°C for
1 min (with variable numbers of cycles), and a final extension phase of
72°C for 10 min. For semiquantitative assessment of IL-18 mRNA,
variable numbers of cycles were used to ensure that amplification
occurred in the linear phase. To exclude the possibility of finding
differences between tubes due to unequal concentrations of cDNA in the
PCR, a PCR using -actin as the internal standard was performed on
each sample. -actin was found to be linear at 27 amplification
cycles, and IL-18 was found to be linear at 29 amplification cycles.
The primers used for IL-18 (433 bp) were 5'-ACTGTACAACCGCAGTAATACGG-3'
(sense) and 5'-AGTGAACATTACAGATTTATCCC-3 (antisense), and for
-actin (617 bp) 5'-GTCAGAAGGACTCCTATGTG-3' (sense) and
5'-GCTCGTTGCCAATAGTGATG-3' (antisense). PCR products were
visualized by agarose gel electrophoresis.
Determination of bacterial outgrowth
At 24 and 48 h after infection, mice were anesthetized by 7.0 ml/kg FFM (fentanyl citrate 0.079 mg/ml, fluanisone 2.5 mg/ml, midazolam 1.25 mg/ml in H2O) i.p. and sacrificed by bleeding out the vena cava inferior. Blood was collected in EDTA-containing tubes. Whole lungs were harvested and homogenized at 4°C in four volumes of sterile saline using a tissue homogenizer (Biospec Products, Bartlesville, OK). Serial 10-fold dilutions were made in sterile saline and 50-µl volumes were plated onto blood agar plates. In addition, 20-µl volumes of blood were plated. Plates were incubated at 37°C at 5% CO2, and CFUs were counted after 16 h.
Preparation of lung tissue for cytokine measurements and Western blot analysis
Lung homogenates were diluted 1/2 in lysis buffer containing 300 mM NaCl, 30 mM Tris, 2 mM MgCl2, 2 mM CaCl2, 1% Triton X-100, and pepstatin A, leupeptin, and aprotinin (all 20 ng/ml, pH 7.4) and incubated at 4°C for 30 min. Homogenates were centrifuged at 1500 x g at 4°C for 15 min, and supernatants were stored at -20°C until assays were performed.
Electrophoresis and Western blotting
For Western blots, 5 µg of total protein was reduced with SDS sample buffer containing 20% 2-ME and denatured for 5 min at 95°C. SDS-PAGE using a 15% polyacrylamide gel was done according to Laemmli (27) at a constant voltage of 200 V. The proteins were transferred to Immobilon membrane (Millipore, Bedford, MA) using Tris-glycine buffer containing 20% methanol. The transfer was performed at a constant amperage of 0.33 A for 60 min. Nonspecific binding sites on the membrane were blocked by incubation in PBST buffer (PBS with 0.05% Tween 20 (v/v)) containing 2% nonfat dry milk (w/v) at 4°C overnight followed by incubation with primary Ab, i.e., 3 µg of purified rat anti-mouse IL-18 mAb (R&D Systems, Abingdon, U.K.) for 1 h at room temperature. After three washes with PBST buffer containing 0.2% nonfat dry milk (w/v), the membrane was incubated with peroxidase-conjugated rabbit anti-rat IgG Abs (P0450; DAKO, Glostrup, Denmark) in a 1/2000 dilution at room temperature. After washing, the IL-18 bands were visualized using the ECL Western blotting detection system (Boehringer Ingelheim, Ingelheim, Germany). Recombinant mouse (rm)pro-IL-18 and mature IL-18 (both 2 µg) were used as standards. rmIL-18 was obtained from R&D Systems; rmpro-IL-18 was kindly provided by Dr. C. A. Dinarello (University of Colorado Health Sciences Center, Denver, CO) (28).
Bronchoalveolar lavage
The trachea was exposed through a midline incision and canulated with a sterile 22-gauge Abbocath-T catheter (Abott, Sligo, Ireland). Bronchoalveolar lavage was performed by instilling 0.5-ml aliquots of sterile saline. Approximately 1 ml of bronchoalveolar lavage fluid (BALF) was retrieved per mouse. Total cell numbers were counted from each sample, and BALF differential cell counts were done on cytospin preparations stained with a modified Giemsa stain (Diff-Quick; Baxter Diagnostics, McGraw Park, IL).
Histologic examination
Lungs for histologic examination were harvested at 24 and 48 h after infection, fixed in 10% formaline, and embedded in paraffin. Four-micrometer sections were stained with H&E and analyzed by a pathologist who was blinded for groups.
Reagents
Rabbit anti-murine IL-18 antiserum, kindly donated by Dr. C.
Dinarello, was prepared as described previously (29). The
anti-IL-18 serum contained <10 pg/ml endotoxin as determined by
Limulus assay. Anti-IL-18 antiserum (200 µl) was given
i.p. 1 h before and 24 h after intranasal administration of
bacteria. This dose significantly reduced endotoxin-induced IFN-
release and lethality in mice (20). Rabbit serum
(Sigma-Aldrich, St. Louis, MO) was used as control. Polyclonal sheep
anti-murine IL-12 was administered at a dose of 200 µg i.p.
1 h before infection with S. pneumoniae. Anti-IL-12 was
prepared as described previously (30) and was kindly
supplied by the Bioanalytical Sciences Department of Genetics Institute
(Cambridge, MA). Sheep IgG (Sigma-Aldrich) was used as a control.
Assays
IL-18, TNF, IL-12, IFN-, macrophage inflammatory protein-2
(MIP-2), and KC were measured by ELISAs according to the
instructions of the manufacturer (R&D Systems).
Statistical analysis
All data are expressed as mean ± SE. Differences between groups were analyzed by Mann-Whitney U test. Survival was analyzed with Kaplan-Meier. Values of p < 0.05 were considered to represent a statistically significant difference.
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Results |
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To determine whether IL-18 is produced within the pulmonary
compartment during pneumococcal pneumonia, RT-PCR was performed on lung
samples obtained from mice inoculated with saline or at 24 and 48
h after infection with pneumococci. A faint band of IL-18 mRNA was
found in lungs of mice receiving saline, indicating that some IL-18
mRNA is constitutively expressed (Fig. 1
A). Intranasal infection with
S. pneumoniae induced enhanced expression of IL-18 mRNA, as
indicated by equal intensity of -actin bands and clear differences
in band intensity between control and pneumonia samples for IL-18
RT-PCR products.
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B). Infection with S. pneumoniae
slightly increased IL-18 concentrations in lung homogenates, although
this difference was not significant. Recently, it has been demonstrated
that pro-IL-18 is expressed constitutively in the liver and spleen of
mice (28). Because the ELISA used to detect IL-18 binds
both pro-IL-18 and mature IL-18 (data not shown), we performed Western
blot analysis to determine whether IL-18 detected in control lungs and
after infection with S. pneumoniae consists of pro-IL-18 or
mature IL-18. As shown in Fig. 1C, the majority of
constitutive IL-18 in the lung consists of pro-IL-18, but mature IL-18
is also present. Infection with S. pneumoniae resulted in
increases in the amounts of both pro-IL-18 and mature IL-18 at 24 and
48 h after infection. IL-18-/- mice have increased bacterial outgrowth
To determine the role of IL-18 in early host defense against
pneumonia, we compared the bacterial outgrowth in the lungs of WT and
IL-18-/- mice at 24 and 48 h after
intranasal inoculation with 1 x 105 CFU of
S. pneumoniae. At both 24 and 48 h postinfection,
IL-18-/- mice had significantly more bacteria
in their lungs than did WT mice (Fig. 2A). In addition, the number
of IL-18-/- mice that developed bacteremia was
markedly higher compared with WT mice. At 24 h after infection,
67% of the IL-18-/- mice had positive blood
cultures for S. pneumoniae, while none of the WT mice had
bacteria in their blood. At 48 h, all
IL-18-/- mice and only 50% of WT mice were
bacteremic. Despite these differences in early antibacterial defense,
survival did not consistently differ among
IL-18-/- and WT mice. Inoculation of
105 CFU of pneumococci resulted in lethality
between days 2 and 5 in both strains and an overall survival of 1 of 14
IL-18-/- mice and 3 of 14 WT mice
(nonsignificant). In addition, in another experiment with a lower
bacterial inoculum (5 x 104 CFU), mortality
also tended to be higher in IL-18-/- mice than
in WT mice (survival: two of eight IL-18-/-
mice and three of eight WT mice; nonsignificant).
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B). Cell influx in BALF
A marked increase in cell numbers in BALF was found at 24 and
48 h after infection of WT mice with S. pneumoniae as
compared with controls, which was mainly the result of granulocyte
influx (Fig. 3). The number of recruited
granulocytes in the lungs was markedly increased in
IL-18-/- mice compared with WT mice at 24
h after infection (Fig. 3). At 48 h, the number of granulocytes in
BALF did not differ between the two groups.
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In accordance with the cell count in BALF, the lungs of
IL-18-/- mice showed significantly more
inflammatory infiltrates than WT mice at 24 h after inoculation.
As illustrated in Fig. 4A, a
massive inflammatory infiltrate was present in
IL-18-/- mice with vasculitis. Neutrophils were
dominant and filled bronchi, bronchioles, and adjacent alveolar spaces.
In WT mice, the inflammation clearly was more discrete (Fig. 4B). At 48 h after inoculation, the degree of
inflammation was reduced in IL-18-/- mice (Fig. 4C) compared with 24 h but remained higher than in WT
animals (Fig. 4D).
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To determine whether alterations in the expression of cytokines
and/or chemokines contributed to the impaired host defense in
IL-18-/- mice, their concentrations were
measured in lung homogenates. As expected, the lung concentrations of
IFN- were lower in IL-18-/- mice than in WT
mice (Table I). In contrast, CXC
chemokines MIP-2 and KC were higher in IL-18-/-
than in WT mice. Concentrations of TNF and IL-12 were similar in both
groups.
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concentrations (3.3 ± 0.2 ng/g lung vs 3.0 ± 0.2 ng/g in
mice treated with preimmune serum). Anti-IL-18 did reduce IL-12 levels
(18.9 ± 1.6 vs 68.7 ± 14.6 ng/g, p <
0.05). IL-18-mediated effects are independent of endogenous IL-12
The combined action of IL-18 and IL-12 can result in synergistic
effects on host immune cells (7, 8). To study whether
IL-12 contributes to host defense against S. pneumoniae, we
induced pneumonia in IL-12-/- and WT mice.
Bacterial outgrowth in lungs (Fig. 5) and
blood (data not shown) appeared indistinguishable between both mouse
strains. Furthermore, survival did not differ between
IL-12-/- mice (5 of 16) and WT mice (2 of 16;
nonsignificant). To determine whether IL-18 exerts its protective
effect through interaction with IL-12, WT and
IL-18-/- mice were injected with a neutralizing
Ab against IL-12 or control Ab 1 h before infection with
pneumococci, and mice were sacrificed after 48 h. Injection of
anti-IL-12 in WT mice did not significantly influence bacterial
outgrowth in the lung compared with control, confirming the results
obtained with IL-12-/- mice (Fig. 6). Again,
IL-18-/- mice had more bacterial outgrowth in
the lungs compared with WT mice after infection with S.
pneumoniae. Administration of anti-IL-12 to
IL-18-/- mice did not influence bacterial
outgrowth in comparison with IL-18-/- mice that
received a control Ab. These data indicate that IL-18 has
IL-12-independent effects in host defense to pneumococcal pneumonia.
IL-12 did interact to enhance IFN- production in lungs, i.e.,
IL-12-/- mice had lower IFN- concentrations
in their lungs than did WT mice after induction of pneumonia, and
anti-IL-12 treatment reduced IFN- levels in lungs of both WT and
IL-18-/- mice (Table II).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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production from T and NK cells in the presence of costimulatory
signals, especially together with IL-12 (12). Recent
studies have demonstrated that IL-18 has many other biologic
activities, including stimulation of proliferation and cytotoxicity of
T and NK cells, induction of Fas ligand expression, potentiation of
IL-12-induced activation of Th1 cells, and the induction of cytokine
production (7, 8, 11, 12, 13, 14, 15, 16, 17). IL-18 is produced during
clinical infection and in various animal models of infection (5, 6, 20, 21, 23, 31). Importantly, endogenous IL-18 has a
protective role in mice during infection with Y.
enterolitica and the intracellular pathogens L. major
and S. typhimurium (21, 22, 23). In the present study we demonstrate the important role of IL-18 during Gram-positive bacterial infection in the lung. IL-18 mRNA and IL-18 protein, mainly consisting of pro-IL-18, were found to be constitutively expressed within the lung. This is in agreement with earlier studies, which showed that IL-18 mRNA is expressed in lungs and other organs of normal mice (21, 28, 32, 33, 34). Alveolar macrophages, the resident phagocytes within the airways, are likely important producers of IL-18 within the lung, because IL-18 is known to be mainly produced by activated macrophages (19). Cameron et al. (32) reported that the majority of IL-18 mRNA within lung tissue of mice was localized to airway epithelium cells, although inflammatory cells, mostly lymphocytes, within the airway wall and parenchyma also expressed IL-18 mRNA. In addition, IL-18 mRNA expression was also found in granulocytes present in the lungs of LPS-treated mice. As demonstrated by Western blot analysis, constitutively expressed IL-18 mainly consisted of biologically inactive pro-IL-18, although also low concentrations of mature IL-18 were present. Intranasal infection with S. pneumoniae induced the up-regulation of IL-18 mRNA expression, and a modest increase in the concentrations of both pro-IL-18 and mature IL-18 protein in the lung. Importantly, bacterial outgrowth in both lungs and blood was significantly increased in the early phase of infection in IL-18-/- mice compared with WT mice. Furthermore, the role of endogenous IL-18 was confirmed by the finding that anti-IL-18 treatment was associated with an enhanced outgrowth of pneumococci in lungs of WT mice when compared with WT mice treated with a control Ab. These data suggest that, although the release of IL-18 locally within the lung is not strongly up-regulated during pneumococcal pneumonia, IL-18 plays an important regulatory role in the early localized antimicrobial host defense against S. pneumoniae.
Pneumonia is characterized by the recruitment of phagocytic cells, mainly granulocytes, to the site of infection (35). Granulocyte influx in the lung was markedly increased in IL-18-/- mice at 24 h after S. pneumoniae inoculation. Accordingly, a severe bronchopneumonia with signs of vasculitis was observed in the lungs of IL-18-/- mice at this time point. The inflammatory infiltrate was much more discrete in the lungs of WT mice. At 48 h, the number of granulocytes in BALF and the degree of inflammation were reduced in IL-18-/- mice compared with 24 h but remained higher than in WT animals. The increased recruitment of granulocytes to the alveolar compartment of IL-18-/- mice may at least in part have been mediated by the elevated lung concentrations of the CXC chemokines MIP-2 and KC, which are known to contribute to granulocyte attraction to sites of bacterial infection in the lung (36, 37). Normally, granulocytes serve a protective role in the defense against pneumonia, as indicated by studies in which Abs against either MIP-2 or the type 2 CXCR diminished granulocyte recruitment and bacterial clearance during Klebsiella and Pseudomonas pneumonia respectively (36, 38), and conversely by an investigation in which transgenic overexpression of KC in the lungs resulted in an enhanced granulocyte recruitment to lungs and an improved bacterial clearance (37). However, we consider it likely that the increased lung inflammation observed in IL-18-/- mice is a reflection of an increased proinflammatory stimulus provided by the higher bacterial load. Indeed, in systemic sterile inflammation, induced by i.p. injection of Escherichia coli endotoxin in mice, anti-IL-18 reduced neutrophil accumulation in various tissues, including the lungs, which was associated with reduced lung concentrations of MIP-2 (20). Furthermore, IL-18 has been reported to increase rather than to inhibit the production of IL-8, the human prototypic CXC chemokine, in vitro (14).
Previous studies have demonstrated that locally produced cytokines play an important role in the regulation of host defense against bacterial pneumonia (4). In murine pneumonia caused by S. pneumoniae or Klebsiella pneumoniae, the absence of the proinflammatory cytokine TNF was associated with enhanced bacterial outgrowth in the lung and increased mortality (25, 39, 40). However, neutralization of the anti-inflammatory cytokine IL-10 impaired bacterial clearance from the lung in these models (24, 41). Hence, a local proinflammatory milieu seems required for an adequate antibacterial defense at the site of the infection. Our present findings are in line with the documented proinflammatory properties of IL-18, revealing that this cytokine, like TNF, plays a protective role in host defense against bacterial respiratory tract infection.
IL-18, originally named IFN--inducing factor, has traditionally been
viewed as an important stimulator, together with IL-12, of IFN-
production (19). In accordance,
IL-18-/- mice had lower IFN- concentrations
in their lungs than did WT mice during pneumonia. Previous studies have
suggested that IL-12 and IFN- are involved in protective immunity
during pneumonia (42, 43). However, data from the present
and previous studies indicate that the protective role of endogenous
IL-18 is mediated via IL-12- and IFN--independent mechanisms.
Indeed, IL-12-/- mice demonstrated a normal
defense to pneumococcal pneumonia, which is in line with earlier
investigations with IL-12p35-/- mice in this
model (44). Furthermore, injection of anti-IL-12 did
not influence pneumococcal outgrowth in either WT or
IL-18-/- mice. These findings contrast with an
earlier report in which anti-IL-12 treatment was found to hamper
host defense in Klebsiella pneumonia (42).
Possibly, the role of IL-12 is more prominent during Gram-negative
(K. pneumoniae) pneumonia than in Gram-positive (S.
pneumoniae) pneumonia. Recent data generated in our laboratory
indicate that the role of endogenous IFN- is opposite to the role of
endogenous IL-18 in this pneumonia model (45). Indeed,
both IFN-R-deficient and IFN--deficient mice demonstrated a
reduced outgrowth of pneumococci when compared with their respective WT
strains in association with a diminished influx of neutrophils to BALF.
Survival was not influenced by IFN- deficiency. These results in
mice lacking IFN- activity, which were repeatedly confirmed in many
experiments, contrast with a previous study by Rubins et al.
(43) reporting an increased mortality of
IFN--/- mice. These authors, who did not
evaluate the effect of IFN- deficiency on bacterial outgrowth, used
much larger inocula of S. pneumoniae (up to
108 CFU), associated with rapid mortality, which
may have less relevance for clinical pneumonia. It should be noted that
in the current studies anti-IL-18 treatment of WT mice was not
associated with reduced IFN- concentrations, contrasting with
results obtained in IL-18-/- mice. Although a
clear explanation for this is not available, all in all these data
strongly favor a role for IL-18 during pneumococcal pneumonia that is
unrelated to effects of IL-12 or IFN-.
Despite the availability of potent antimicrobial agents, pneumonia remains an important cause of illness and mortality worldwide. The Gram-positive bacterium S. pneumoniae is the most frequently isolated pathogen in patients with community-acquired pneumonia (1, 2). Therefore, insight into the immune response against S. pneumoniae may contribute to potential adjuvant immunomodulatory therapies. In this study we demonstrate that endogenous IL-18 has a protective role in the early immune response during murine pneumococcal pneumonia by promoting bacterial clearance from the lung and delaying the progression to systemic infection. This is in line with previous studies which demonstrated that local inflammation, in which proinflammatory cytokines play a pivotal role, is essential for local host defense against respiratory pathogens (4).
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Acknowledgments |
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Footnotes |
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2 Abbreviations used in this paper: WT, wild-type; rm, recombinant mouse; BALF, bronchoalveolar lavage fluid; MIP-2, macrophage inflammatory protein-2.
Received for publication May 17, 2001. Accepted for publication November 2, 2001.
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W. J. Wiersinga, C. W. Wieland, G. J. W. van der Windt, A. de Boer, S. Florquin, A. Dondorp, N. P. Day, S. J. Peacock, and T. van der Poll Endogenous Interleukin-18 Improves the Early Antimicrobial Host Response in Severe Melioidosis Infect. Immun., August 1, 2007; 75(8): 3739 - 3746. [Abstract] [Full Text] [PDF]
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K. Sun, S. L. Salmon, S. A. Lotz, and D. W. Metzger Interleukin-12 Promotes Gamma Interferon-Dependent Neutrophil Recruitment in the Lung and Improves Protection against Respiratory Streptococcus pneumoniae Infection Infect. Immun., March 1, 2007; 75(3): 1196 - 1202. [Abstract] [Full Text] [PDF]
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M. C. Dessing, A. F. de Vos, S. Florquin, and T. van der Poll Monocyte Chemoattractant Protein 1 Does Not Contribute to Protective Immunity against Pneumococcal Pneumonia Infect. Immun., December 1, 2006; 74(12): 7021 - 7023. [Abstract] [Full Text] [PDF]
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 D. M. Kelly, C. M. Greene, G. Meachery, M. O'Mahony, P. M. Gallagher, C. C. Taggart, S. J. O'Neill, and N. G. McElvaney Endotoxin Up-regulates Interleukin-18: Potential Role for Gram-Negative Colonization in Sarcoidosis Am. J. Respir. Crit. Care Med., November 15, 2005; 172(10): 1299 - 1307. [Abstract] [Full Text] [PDF]
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 L. Fernandez-Lago, A. Orduna, and N. Vizcaino Reduced interleukin-18 secretion in Brucella abortus 2308-infected murine peritoneal macrophages and in spleen cells obtained from B. abortus 2308-infected mice J. Med. Microbiol., June 1, 2005; 54(6): 527 - 531. [Abstract] [Full Text] [PDF]
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G K Paterson, C E Blue, and T J Mitchell Role of interleukin-18 in experimental infections with Streptococcus pneumoniae J. Med. Microbiol., April 1, 2005; 54(4): 323 - 326. [Abstract] [Full Text] [PDF]
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 J. Branger, S. Florquin, S. Knapp, J. C. Leemans, J. M. Pater, P. Speelman, D. T. Golenbock, and T. van der Poll LPS-binding protein-deficient mice have an impaired defense against Gram-negative but not Gram-positive pneumonia Int. Immunol., November 1, 2004; 16(11): 1605 - 1611. [Abstract] [Full Text] [PDF]
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C. Nakasone, K. Kawakami, T. Hoshino, Y. Kawase, K. Yokota, K. Yoshino, K. Takeda, S. Akira, and A. Saito Limited Role for Interleukin-18 in the Host Protection Response to Pulmonary Infection with Pseudomonas aeruginosa in Mice Infect. Immun., October 1, 2004; 72(10): 6176 - 6180. [Abstract] [Full Text] [PDF]
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K. F. van der Sluijs, L. J. R. van Elden, M. Nijhuis, R. Schuurman, J. M. Pater, S. Florquin, M. Goldman, H. M. Jansen, R. Lutter, and T. van der Poll IL-10 Is an Important Mediator of the Enhanced Susceptibility to Pneumococcal Pneumonia after Influenza Infection J. Immunol., June 15, 2004; 172(12): 7603 - 7609. [Abstract] [Full Text] [PDF]
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J. Branger, S. Knapp, S. Weijer, J. C. Leemans, J. M. Pater, P. Speelman, S. Florquin, and T. van der Poll Role of Toll-Like Receptor 4 in Gram-Positive and Gram-Negative Pneumonia in Mice Infect. Immun., February 1, 2004; 72(2): 788 - 794. [Abstract] [Full Text] [PDF]
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 B. Liu, I. Mori, M. J. Hossain, L. Dong, K. Takeda, and Y. Kimura Interleukin-18 improves the early defence system against influenza virus infection by augmenting natural killer cell-mediated cytotoxicity J. Gen. Virol., February 1, 2004; 85(2): 423 - 428. [Abstract] [Full Text] [PDF]
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V. Cusumano, A. Midiri, V. V. Cusumano, A. Bellantoni, G. De Sossi, G. Teti, C. Beninati, and G. Mancuso Interleukin-18 Is an Essential Element in Host Resistance to Experimental Group B Streptococcal Disease in Neonates Infect. Immun., January 1, 2004; 72(1): 295 - 300. [Abstract] [Full Text] [PDF]
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D. H. Dockrell, H. M. Marriott, L. R. Prince, V. C. Ridger, P. G. Ince, P. G. Hellewell, and M. K. B. Whyte Alveolar Macrophage Apoptosis Contributes to Pneumococcal Clearance in a Resolving Model of Pulmonary Infection J. Immunol., November 15, 2003; 171(10): 5380 - 5388. [Abstract] [Full Text] [PDF]
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S. Weijer, M. E. Sewnath, A. F. de Vos, S. Florquin, K. van der Sluis, D. J. Gouma, K. Takeda, S. Akira, and T. van der Poll Interleukin-18 Facilitates the Early Antimicrobial Host Response to Escherichia coli Peritonitis Infect. Immun., October 1, 2003; 71(10): 5488 - 5497. [Abstract] [Full Text] [PDF]
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E. Saeland, G. Vidarsson, J. H. W. Leusen, E. van Garderen, M. H. Nahm, H. Vile-Weekhout, V. Walraven, A. M. Stemerding, J. S. Verbeek, G. T. Rijkers, et al. Central Role of Complement in Passive Protection by Human IgG1 and IgG2 Anti-pneumococcal Antibodies in Mice J. Immunol., June 15, 2003; 170(12): 6158 - 6164. [Abstract] [Full Text] [PDF]
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M. J. Schultz, S. Knapp, S. Florquin, J. Pater, K. Takeda, S. Akira, and T. van der Poll Interleukin-18 Impairs the Pulmonary Host Response to Pseudomonas aeruginosa Infect. Immun., April 1, 2003; 71(4): 1630 - 1634. [Abstract] [Full Text]
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 J. A. Gracie, S. E. Robertson, and I. B. McInnes Interleukin-18 J. Leukoc. Biol., February 1, 2003; 73(2): 213 - 224. [Abstract] [Full Text] [PDF]
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