Comparative evaluation of Duopath Legionella lateral flow assay against the conventional culture method using Legionella pneumophila and Legionella anisa strains

Duopath Legionella is a new immunochromatographic assay for the identification of Legionella pneumophila and Legionella spp. As excellent specificity has been previously reported for this kit, we attempted an evaluation of its sensitivity using L. pneumophila serogroup 1 and Legionella anisa strains. Bacterial suspensions of L. pneumophila at concentrations of 1.2 x 10(8) cfu/ml and 1.2 x 10(7) cfu/ml were detected, but those below 1.2 x 10(6) cfu/ml were not recognized by the Duopath kit. After centrifugation and the sediment resuspension, a 2.8 x 10(7) cfu/ml concentration of bacterial suspension showed a positive result, but negative results were obtained below 2.8 x 10(6) cfu/ml. Also, bacterial suspension with concentrations of 3.2 x 10(9) cfu/ml and 1.4 x 10(9) cfu/ml after centrifugation of L.anisa were detected, but those below 3.2 x 10(8) cfu/ml and 1.4 x 10(8) cfu/ml after centrifugation were not recognized by the Duopath kit. Meanwhile, this kit was less sensitive to the L. pneumophila serogroup 1 suspension, and was more sensitive to the L. pneumophila serogroup 2 and L.anisa than the Binax NOW immunochromatographic kit. It was realized that the sensitivity of this kit is too low for determining the presence of Legionella in water samples. Although this kit may have excellent specificity, it has low sensitivity.

[Cloning and expression of PAL gene of Legionella pneumophila]

OBJECTIVE

To develop DNA vaccine for Legionella pneumophila.

METHODS

PAL gene of Legionella pneumophila was amplified with PCR. The amplified DNA was ligated to pcDNA3.1(+) vector. The recombinant plasmid, which was identified by restriction analysis, PCR and sequence analysis, was named pcDNA3.1-PAL. The NIH3T3 cells were transfected with the recombinant plasmid pcDNA3.1-PAL by Lipofection. Transient and stable expression products of the PAL gene were detected by immunofluorescence and RT-PCR.

RESULTS

The recombinant plasmid pcDNA3.1-PAL expressed PAL protein in the eukaryotic cell NIH3T3.

CONCLUSION

This study has built a foundation for the development of PAL gene DNA vaccine for Legionella pneumophila.

[Investigation of Legionella pneumophila seropositivity in the professional long distance drivers as a risky occupation]

Contaminated water sources, reservoirs and systems such as evaporative condensers of air-conditioners are known to be the main transmission routes of Legionella spp. which are ubiquitous aquatic bacteria. By virtue of this point the aim of this study was to investigate the rate of Legionella pneumophila seropositivity in a profession considered as risky due to the direct and prolonged exposure to air-conditioning and air-circulating systems. For this purpose, in the period of February-August 2004 a total of 79 male subjects (63 were bus drivers and 16 were driver assistants) who were continously travelling to two different route (South part as hot climate and Middle/North parts as cold climate of Turkey) from Denizli province coach station (a province located in internal Aegian where accepted as crossroads), were included to the study. The mean age and mean working duration of bus drivers were 43.0 +/- 1.1 years and 20.0 +/- 1.1 years, respectively, while these values were 22.5 +/- 0.9 years and 4.0 +/- 0.6 years, respectively, for the drivers' assistants. The serum samples collected from the subjects were screened by a commercial indirect immunofluorescence method (Euroimmun, Germany) using L. pneumophila serogrup 1-14 antigens for the presence of specific antibodies. Additionally, air-conditioners' moisture exhaust samples of the busses in which seropositive subjects travelling with have been examined by culture and 5S rRNA gene targeted polymerase chain reaction (PCR) methods, for the presence of Legionella spp. The overall L. pneumophila seropositivity rate was detected as 15.2% (12/79). This rate was 19% (12/63) for bus drivers while all of the drivers' assistants were found seronegative. The seropositivity rate was found statistically higher in the personnel who were travelling to the hot climates (10/36, 27.8%) than those who travel to cold climates (2/43, 4.6%), (p < 0.05). The culture and PCR yielded negative results for Legionella spp. in the exhaust samples collected from the air-conditioners of the busses in which seropositive drivers travel. Our data indicated that long distance bus drivers were chronically exposed to this pathogen and this may be considered as an occupational risk factor for legionellosis especially for drivers who travel to the west and south parts of our country (mean temperature in August 2004: 30-35 degrees C), since the bus air-conditioning and air-circulating systems are active during the travel. Further studies on air spreading of Legionella in intercity buses can reveal how the exposure occurs for bus drivers.

Effect of flow regimes on the presence of Legionella within the biofilm of a model plumbing system

AIMS

Stagnation is widely believed to predispose water systems to colonization by Legionella. A model plumbing system was constructed to determine the effect of flow regimes on the presence of Legionella within microbial biofilms.

METHODS AND RESULTS

The plumbing model contained three parallel pipes where turbulent, laminar and stagnant flow regimes were established. Four sets of experiments were carried out with Reynolds number from 10,000 to 40,000 and from 355 to 2,000 in turbulent and laminar pipes, respectively. Legionella counts recovered from biofilm and planktonic water samples of the three sampling pipes were compared with to determine the effect of flow regime on the presence of Legionella. Significantly higher colony counts of Legionella were recovered from the biofilm of the pipe with turbulent flow compared with the pipe with laminar flow. The lowest counts were in the pipe with stagnant flow.

CONCLUSIONS

We were unable to demonstrate that stagnant conditions promoted Legionella colonization.

SIGNIFICANCE AND IMPACT OF THE STUDY

Plumbing modifications to remove areas of stagnation including deadlegs are widely recommended, but these modifications are tedious and expensive to perform. Controlled studies in large buildings are needed to validate this unproved hypothesis.

Role of Toll-like receptor 2 in recognition of Legionella pneumophila in a murine pneumonia model

Legionella pneumophila is an intracellular organism and the major aetiological agent of Legionnaires' disease. Although recent progress has identified Toll-like receptors (TLRs) as receptors for recognition of pathogen-associated molecular patterns in a variety of micro-organisms, understanding the contribution of TLRs to the host response in L. pneumophila infection is still limited. This study examined the roles of TLR2 and TLR4 in murine L. pneumophila pneumonia and an in vitro infection model using bone-marrow-derived macrophages. TLR2-deficient mice, but not TLR4-deficient mice, demonstrated higher lethal sensitivity to pulmonary challenge with L. pneumophila than wild-type mice (P<0.05). Although no differences in pulmonary bacterial burden were observed among the mouse strains examined, lower values of macrophage inflammatory protein-2 (MIP-2), keratinocyte-derived cytokine and interleukin (IL)-6 and higher IL-12 levels were noted in lung homogenates of TLR2-deficient mice compared with the wild-type control and TLR4-deficient mice. Recruitment of inflammatory cells, particularly neutrophils, was severely disturbed in the lungs of TLR2-deficient mice. Reduced MIP-2 production was demonstrated in bone-marrow-derived macrophages from TLR2-deficient mice in response to live L. pneumophila and purified LPS of this strain, but not Escherichia coli LPS. These data highlight the involvement and importance of TLR2 in the pathogenesis of L. pneumophila pneumonia in mice. The results showed that TLR2-mediated recognition of Legionella LPS and subsequent chemokine-dependent cellular recruitment may be a crucial host innate response in L. pneumophila pneumonia.

[In vitro expression of Lgeionella pneumophila pilE gene and its immunogenicity]

OBJECTIVE

To construct a recombinant plasmid containing Lgeionella pneumophila pilE gene, detect its expression in NIH3T3 cells and evaluate its immunogenicity.

METHODS

PilE gene (LP) was amplified from Legionella pneumophila DNA by PCR and inserted into pcDNA3.1(+) vector to construct the recombinant plasmid pcDNA3.1-pilE, which as verified by restriction endonuclease digestion, PCR and DNA sequencing analysis. NIH3T3 cells were transfected with the recombinant plasmid with Lipofection strategy. Transient and stable pilE gene products were detected by immunofluorescence and Western blotting, respectively. To evaluate the immunogenicity of pcDNA3.1-pilE, the recombinant plasmid was used as a DNA vaccine to immunize female BALB/c mice intramuscularly and the specific antibodies, lymphocyte proliferation response, interferon (IFN)-gamma production and cytotoxic T-lymphocyte response of the immunized mice were detected and evaluated.

RESULTS

The pilE gene of 429 bp in length was amplified. After transfection of NIH3T3 cells with the recombinant plasmid, strong green fluorescence was observed on the cell membrane and inside the cell. A protein with relative molecular mass of 15.7 kD was detected in the transfected cells with Western blotting, suggesting successful protein expression of pilE gene. pcDNA3.1-pilE resulted in much stronger immune response in the immunized mice than pcDNA3.1(+) (P<0.01).

CONCLUSION

The recombinant plasmid containing Lgeionella pneumophila pilE gene constructed in this study is capable of expression in NIH3T3 cells, and can induce specific humoral and cellular immune responses in mice.

Genetic susceptibility and caspase activation in mouse and human macrophages are distinct for Legionella longbeachae and L. pneumophila

Legionella pneumophila is the predominant cause of Legionnaires' disease in the United States and Europe, while Legionella longbeachae is the common cause of the disease in Western Australia. Although clinical manifestations by both intracellular pathogens are very similar, recent studies have shown that phagosome biogeneses of both species within human macrophages are distinct (R. Asare and Y. Abu Kwaik, Cell. Microbiol., in press). Most inbred mouse strains are resistant to infection by L. pneumophila, with the exception of the A/J mouse strain, and this genetic susceptibility is associated with polymorphism in the naip5 allele and flagellin-mediated early activation of caspase 1 and pyropoptosis in nonpermissive mouse macrophages. Here, we show that genetic susceptibility of mice to infection by L. longbeachae is independent of allelic polymorphism of naip5. L. longbeachae replicates within bone marrow-derived macrophages and in the lungs of A/J, C57BL/6, and BALB/c mice, while L. pneumophila replicates in macrophages in vitro and in the lungs of the A/J mouse strain only. Quantitative real-time PCR studies on infected A/J and C57BL/6 mouse bone marrow-derived macrophages show that both L. longbeachae and L. pneumophila trigger similar levels of naip5 expression, but the levels are higher in infected C57BL/6 mouse macrophages. In contrast to L. pneumophila, L. longbeachae has no detectable pore-forming activity and does not activate caspase 1 in A/J and C57BL/6 mouse or human macrophages, despite flagellation. Unlike L. pneumophila, L. longbeachae triggers only a modest activation of caspase 3 and low levels of apoptosis in human and murine macrophages in vitro and in the lungs of infected mice at late stages of infection. We conclude that despite flagellation, infection by L. longbeachae is independent of polymorphism in the naip5 allele and L. longbeachae does not trigger the activation of caspase 1, caspase 3, or late-stage apoptosis in mouse and human macrophages. Neither species triggers caspase 1 activation in human macrophages.

Evaluation of the SAS Legionella Test, a new immunochromatographic assay for the detection of Legionella pneumophila serogroup 1 antigen in urine

This study evaluated a new immunochromatographic assay (SAS Legionella Test) for its ability to detect Legionella pneumophila serogroup 1 antigen in urine. Results were compared with those obtained using the Binax Now urinary antigen test. Sensitivity and specificity were estimated as 82.9% and 99.0%, respectively, for the SAS Legionella Test, and 91.4% and 100%, respectively, for the Binax Now urinary antigen test. The sensitivity of both tests increased to 97.1% (p 0.009) and 94.2% (p 0.7), respectively, if the tests were examined after 1 h.

Largest Outbreak of Legionellosis Associated with Spa Baths

In July 2002, a large outbreak of legionellosis occurred in a bathhouse with spa facilities in Miyazaki Prefecture. Among the visitors, 295, including suspected cases had pneumonia and/or symptoms of fever, coughing, etc. Of these, 37% were hospitalized and 7 died. Clinical samples from 95 mainly inpatients were collected and microbiologically tested at our laboratory. Legionella pneumophila serogroup (SG) 1 was isolated from 3 of 24 in sputum culture, and none of the 3 had been treated effectively with antibiotics at sputa collection. L. pneumophila antigen in urine was detected by using enzyme immunoassay and/or immunochromatographic kits in 23 of 75 patients. Serum antibodies to L. pneumophila SG1 and Legionella dumoffii were detected in 5 each of 66 patients--9 cases including a case at mixed infection-by microplate agglutination test and/or indirect immunofluorescence assay. At our laboratory, 32 were diagnosed with legionellosis. In this outbreak, 14 were diagnosed at other laboratories, resulting in 46 confirmed cases. Urine antigen was detected more frequently by Binax NOW immunochromatographic assay than by Biotest EIA-31% versus 16% of cases tested. Both assays detected urine antigen only in samples collected within 4 weeks after onset. Antigen concentration in urine enhanced sensitivity-58% and 51%-and extended the period of antigen detection beyond 5 weeks. Both antibody titers to L. pneumophila SG1 and L. dumoffii in more than 90% of sera collected within 3 weeks after onset were < 1:16. The rate of serum antibody titer to > or = 1:128 within 3 weeks was 1.6%, during 4 to 6 weeks less than 10%, and after 7 weeks or more 8 to 25%. After an administrative report was published, L. pneumophila DNA in sputa was detected in 5 of 17 patients by nested PCR, resulting in extra 3 cases. Altogether, urinary antigen detection and PCR were more effective in laboratory diagnostic tests than culture and serology. Culture combined with molecular epidemiology is critical, however, for confirming the source of infection.

Identification and serotyping of atypical Legionella pneumophila strains isolated from human and environmental sources

AIMS

To validate identification methods for Legionella pneumophila strains that cannot be serotyped into the known serogroups and to characterize their antigenic diversity.

METHODS AND RESULTS

Fifty L. pneumophila strains that could not be serogrouped, but which had been confirmed as L. pneumophila by mip gene sequencing, were further identified phenotypically. We used (i) MONOFLUO anti-Legionella Staining Reagent (Bio-Rad) (50/50), (ii) an in-house prepared immunoblot assay for the detection of L. pneumophila- specific Mip protein epitope (50/50), (iii) fatty acid analysis using the Microbial Identifications System (MIDI) (47/50) and (iv) Oxoid agglutination tests (44/50). The serological diversity was further characterized by testing with five serogroup-cross-reactive monoclonal antibodies, resulting in nine phenons.

CONCLUSIONS

The division of L. pneumophila into 15 serogroups does not reflect the serogroup heterogeneity. Results of these tests indicate that there are more serogroups.

SIGNIFICANCE AND IMPACT OF THE STUDY

MONOFLUO anti-Legionella Staining Reagent is the only commercially available tool for identifying atypical strains of L. pneumophila. If necessary for epidemiological purposes, the antigenic heterogeneity of these strains can be analysed by monoclonal antibodies.

Legionnaires' disease: when an 'outbreak' is not an outbreak

During August 2006, there was a large increase in non-travel related legionella cases throughout England and in the Netherlands.

Innate recognition of intracellular bacteria

The molecular repertoire for innate recognition of bacterial pathogens has expanded rapidly in the past decade. These immunosensors include Toll-like receptors and the more recently defined NOD-like receptors (NLRs): NODs, NALPs, NAIP and IPAF. Toll-like receptors signal from the cell surface or endosome upon ligand binding, whereas NLRs are activated by characteristic bacterially derived molecules, such as peptidoglycan, RNA, toxins and flagellin, in the cytosol. Studies using animal and culture models of bacterial infection indicate a pro-inflammatory role for NLRs, mediated by signaling through nuclear transcription factor kappaB and activation of caspase-1 by the inflammasome. These data also support a synergistic role for extracellular and intracellular bacterial sensing in regulating inflammation. In humans, NLR mutations are often associated with autoinflammatory syndromes, suggesting a complex role for cytosolic surveillance in systemic innate immunity.

[Treatment for Legionnaires' disease. Macrolides or quinolones?]

BACKGROUND

Macrolides and fluoroquinolones are the recommended treatment for Legionnaires' disease. The aim of our study was to analyze the clinical efficacy of clarithromycin, azithromycin and levofloxacin in patients with Legionnaires' disease.

METHODS

Prospective, observational study involving all adult patients with Legionella pneumophila pneumonia attended at Hospital Universitario Vall d'Hebron (Barcelona, Spain) from January 2001 to December 2004. Duration of fever, length of hospital stay and mortality were compared among 52 patients treated with clarithromycin, 43 with azithromycin and 18 with levofloxacin.

RESULTS

The proportion of patients with risk factors for Legionnaires' disease, the initial severity of the pneumonia and the number of patients who required intensive care unit admission were similar in patients treated with clarithromycin, azithromycin and levofloxacin. In-hospital mortality was 5.3%. There were no significant differences in fever duration, length of hospital stay or mortality among the 3 groups of patients.

CONCLUSION

In our experience, clarithromycin, azithromycin and levofloxacin were all efficacious for the treatment of Legionnaires' disease.

The Legionella pneumophila effector SidJ is required for efficient recruitment of endoplasmic reticulum proteins to the bacterial phagosome

The virulence of Legionella pneumophila is dependent on the Dot/Icm type IV protein secretion system, which translocates effectors into infected cells. A large number of such translocated proteins have been identified, but few of these proteins are necessary for intracellular replication of the pathogen, making it difficult to correlate these genes with specific cell-biological events associated with L. pneumophila infection. We report here the identification and characterization of a family of two substrates, SidJ and SdjA, with distinctive phenotypes. In contrast to many Dot/Icm substrates, whose expression levels are elevated when bacteria are grown to postexponential phase, SidJ is produced at a constant rate during the entire bacterial growth cycle. Mutation in sidJ causes a significant growth defect in both macrophage and amoeba hosts, but an sdjA mutant is detectably defective only in protozoan hosts. However, in the amoeba host a mutant lacking both sidJ and sdjA does not display a more severe growth defect than the sidJ mutant. Despite its significant intracellular growth defect, the sidJ mutant is still able to effectively evade fusion with lysosomes. Importantly, recruitment of endoplasmic reticulum (ER) proteins by vacuoles containing the sidJ mutant was considerably delayed in both mammalian and amoeba cells. Our results suggest that SidJ modulates host cellular pathways, contributing to the trafficking or retention of ER-derived vesicles to L. pneumophila vacuoles.

Evaluation of two new immunochromatographic assays (Rapid U Legionella antigen test and SD Bioline Legionella antigen test) for detection of Legionella pneumophila serogroup 1 antigen in urine

We evaluated two new immunochromatographic assays for their abilities to detect Legionella pneumophila serogroup 1 antigen in urine. The results were compared with those obtained by the Binax NOW urinary antigen test. The sensitivities and specificities were estimated to be 71.2% and 96.6%, respectively, for the Rapid U test; 31.5% and 98.9%, respectively, for the SD Bioline test; and 91.8% and 100%, respectively, for the Binax NOW test.

Role of Toll-like receptor 9 in Legionella pneumophila-induced interleukin-12 p40 production in bone marrow-derived dendritic cells and macrophages from permissive and nonpermissive mice

The progression of Legionella pneumophila infection in macrophages is controlled by the Lgn1 gene locus, which expresses the nonpermissive phenotype in cells from BALB/c mice but the permissive phenotype in cells from A/J mice. Activation of dendritic cells and macrophages by L. pneumophila is mediated by the pathogen recognition receptor Toll-like receptor 2 (TLR2); furthermore, Legionella induces innate and adaptive immune cytokines by the MyD88-dependent pathway. TLR9 is coupled to MyD88 and mediates the production of interleukin-12 (IL-12) in dendritic cells infected with other facultatively intracellular pathogens. In the current study, L. pneumophila growth in dendritic cells from BALB/c and A/J mice was examined along with the role of TLR9 in the induction of IL-12 in these cells. Dendritic cells from both strains were nonpermissive for L. pneumophila intracellular growth, suggesting that the products of the Lgn1 gene locus that control intracellular growth in macrophages do not control the growth of Legionella in dendritic cells. In addition, chloroquine treatment suppressed IL-12 p40 production in response to Legionella treatment in dendritic cells and macrophages from BALB/c and A/J mice. Furthermore, the TLR9 inhibitor ODN2088 suppressed the Legionella-induced IL-12 production in dendritic cells from both mouse strains. These results suggest that L. pneumophila is similar to other intracellular bacteria in that it stimulates the production of immune-transitioning cytokines, such as IL-12, through activation of TLR9 and that this receptor provides a common mechanism for sensing these types of microbes and inducing innate and adaptive immunity.

Atypical pathogens as etiologic agents in hospitalized patients with community-acquired pneumonia in Korea: a prospective multi-center study

Local epidemiologic data on the etiologies of patients hospitalized with community-acquired pneumonia (CAP) is needed to develop guidelines for clinical practice. This study was conducted prospectively to determine the proportion of atypical bacterial pathogens in adults patients hospitalized with CAP in Korea between October 2001 and December 2002. Microbiological diagnosis was determined by serology for antibodies to Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila. Nucleic acid of M. pneumoniae and C. pneumoniae in respiratory samples and Legionella antigen in urine samples were detected. The study population consisted of 126 patients (71 males, 55 females), averaging 54.6 yr (SD+/-17.8), whose paired sera were available. An etiologic diagnosis for atypical pathogens was made in 18 patients (14.3%): C. pneumoniae 9 (7.1%), M. pneumoniae 8 (6.3%), and L. pneumophila 3 patients (2.4%). Streptococcus preumoniae and other typical pathogens were isolated from 36 patients (28.6%). Of 126 patients, 16 (12.7%) were admitted to intensive care unit and atypical pathogens were identified in 5 patients (31.3%). Initial clinical features of patients with pneumonia due to atypical, typical or undetermined pathogens were indistinguishable. We conclude that atypical pathogens should be seriously considered in hospitalized patients with CAP, when initiating empiric treatment in Korea.

Cannabinoid Treatment Suppresses the T-Helper Cell-Polarizing Function of Mouse Dendritic Cells Stimulated withLegionella pneumophilaInfection

Marijuana cannabinoids, such as delta-9-tetrahydrocannabinoid (THC), suppress type 1 T-helper 1 (Th1) immunity in a variety of models, including infection with the intracellular pathogen Legionella pneumophila (Lp). To examine the cellular mechanism of this effect, bone marrow-derived dendritic cells (DCs) were purified from BALB/c mice and studied following infection and drug treatment. DCs infected in vitro with Lp were able to protect mice when injected prior to a lethal Lp infection; however, the immunization potential of the Lp-loaded cells along with Th1 cytokine production was attenuated by THC treatment at the time of in vitro infection. In addition, THC-treated and Lp-loaded DCs were poorly stimulated in culture-primed splenic CD4(+) T cells to produce interferon-gamma; however, this stimulating deficiency was reversed by adding recombinant interleukin (IL)-12p40 protein to the cultures. Moreover, THC treatment inhibited the expression of DC maturation markers, such as major histocompatibility complex class II and costimulatory molecules CD86 and CD40 as determined by flow cytometry and suppressed the Notch ligand, Del-ta4, as determined by reverse transcription-polymerase chain reaction. However, THC treatment did not affect other DC functions, such as intracellular killing of Lp, determined by colony-forming unit counts of bacteria, and Lp-induced apoptosis, determined by annexin V staining. In conclusion, the data suggest that THC inhibits Th1 activation by targeting essential DC functions, such as IL-12p40 secretion, maturation, and expression of costimulatory and polarizing molecules.

MyD88-dependent responses involving toll-like receptor 2 are important for protection and clearance of Legionella pneumophila in a mouse model of Legionnaires' disease

Legionella pneumophila is a gram-negative facultative intracellular parasite of macrophages. Although L. pneumophila is the causative agent of a severe pneumonia known as Legionnaires' disease, it is likely that most infections caused by this organism are cleared by the host innate immune system. It is predicted that host pattern recognition proteins belonging to the Toll-like receptor (TLR) family are involved in the protective innate immune responses. We examined the role of TLR-mediated responses in L. pneumophila detection and clearance using genetically altered mouse hosts in which the macrophages are permissive for L. pneumophila intracellular replication. Our data demonstrate that cytokine production by bone marrow-derived macrophages (BMMs) in response to L. pneumophila infection requires the TLR adapter protein MyD88 and is reduced in the absence of TLR2 but not in the absence of TLR4. Bacterial growth ex vivo in BMMs from MyD88-deficient mice was not enhanced compared to bacterial growth ex vivo in BMMs from heterozygous littermate controls. Wild-type mice were able to clear L. pneumophila from the lung, whereas respiratory infection of MyD88-deficient mice caused death that resulted from robust bacterial replication and dissemination. In contrast to an infection with virulent L. pneumophila, MyD88-deficient mice were able to clear infections with L. pneumophila dotA mutants, indicating that MyD88-independent responses in the lung are sufficient to clear bacteria that are unable to replicate intracellularly. In vivo growth of L. pneumophila was enhanced in the lungs of TLR2-deficient mice, which resulted in a delay in bacterial clearance. No significant differences were observed in the growth and clearance of L. pneumophila in the lungs of TLR4-deficient mice and heterozygous littermate control mice. Our data indicate that MyD88 is crucial for eliciting a protective innate immune response against virulent L. pneumophila and that TLR2 is one of the pattern recognition receptors involved in initiating this MyD88-dependent response.

Myeloid Differentiation Primary Response Gene (88)– and Toll‐Like Receptor 2–Deficient Mice Are Susceptible to Infection with AerosolizedLegionella pneumophila

BACKGROUND

Toll-like receptors (TLRs) are a family of proteins that orchestrate innate immune responses to microbes. Although pathogens are typically recognized by multiple TLRs, the specific roles of individual TLRs in mediating host protection during in vivo infection are not well understood.

METHODS

We compared the roles of myeloid differentiation primary response gene (88) (MyD88), which regulates signaling through multiple TLRs, and TLR2 in mediating resistance to aerosolized Legionella pneumophila infection in vivo.

RESULTS

In comparison with wild-type mice, MyD88-deficient (MyD88(-/-)) mice had dramatically higher bacterial counts in the lungs, with decreased neutrophil counts in the bronchoalveolar lavage fluid as well as absent cytokine and chemokine production at early time points. By day 6 of infection, the MyD88(-/-) mice developed organizing pneumonia with dissemination of L. pneumophila to the lymph nodes and spleen. TLR2(-/-) mice were also more susceptible to L. pneumophila, with higher bacterial counts in the lung. However, TLR2(-/-) mice produced proinflammatory cytokines, recruited neutrophils to the lung alveoli, and cleared the infection without progression to organizing pneumonia and disseminated disease.

CONCLUSIONS

These results suggest that a MyD88-dependent pathway is required for eradication of L. pneumophila and prevention of organizing pneumonia. TLR2 mediates partial resistance to L. pneumophila, which indicates that additional MyD88-dependent, TLR2-independent pathways are essential for full protection.