CLEC12A Binds to Legionella pneumophila but Has No Impact on the Host's Antibacterial Response

Legionella pneumophila is an intracellular pathogen that can cause severe pneumonia after the inhalation of contaminated aerosols and replication in alveolar macrophages. Several pattern recognition receptors (PRRs) have been identified that contribute to the recognition of L. pneumophila by the innate immune system. However, the function of the C-type lectin receptors (CLRs), which are mainly expressed by macrophages and other myeloid cells, remains largely unexplored. Here, we used a library of CLR-Fc fusion proteins to search for CLRs that can bind the bacterium and identified the specific binding of CLEC12A to L. pneumophila. Subsequent infection experiments in human and murine macrophages, however, did not provide evidence for a substantial role of CLEC12A in controlling innate immune responses to the bacterium. Consistently, antibacterial and inflammatory responses to Legionella lung infection were not significantly influenced by CLEC12A deficiency. Collectively, CLEC12A is able to bind to L. pneumophila-derived ligands but does not appear to play a major role in the innate defense against L. pneumophila.

Source attribution of community-acquired cases of Legionnaires' disease-results from the German LeTriWa study; Berlin, 2016-2019

INTRODUCTION

Sources of infection of most cases of community-acquired Legionnaires' disease (CALD) are unknown.

OBJECTIVE

Identification of sources of infection of CALD.

SETTING

Berlin; December 2016-May 2019.

PARTICIPANTS

Adult cases of CALD reported to district health authorities and consenting to the study; age and hospital matched controls.

MAIN OUTCOME MEASURE

Percentage of cases of CALD with attributed source of infection.

METHODS

Analysis of secondary patient samples for monoclonal antibody (MAb) type (and sequence type); questionnaire-based interviews, analysis of standard household water samples for Legionella concentration followed by MAb (and sequence) typing of Legionella pneumophila serogroup 1 (Lp1) isolates; among cases taking of additional water samples to identify the infectious source as appropriate; recruitment of control persons for comparison of exposure history and Legionella in standard household water samples. For each case an appraisal matrix was filled in to attribute any of three source types (external (non-residence) source, residential non-drinking water (RnDW) source (not directly from drinking water outlet), residential drinking water (RDW) as source) using three evidence types (microbiological results, cluster evidence, analytical-comparative evidence (using added information from controls)).

RESULTS

Inclusion of 111 study cases and 202 controls. Median age of cases was 67 years (range 25-93 years), 74 (67%) were male. Among 65 patients with urine typable for MAb type we found a MAb 3/1-positive strain in all of them. Compared to controls being a case was not associated with a higher Legionella concentration in standard household water samples, however, the presence of a MAb 3/1-positive strain was significantly associated (odds ratio (OR) = 4.9, 95% confidence interval (CI) 1.7 to 11). Thus, a source was attributed by microbiological evidence if it contained a MAb 3/1-positive strain. A source was attributed by cluster evidence if at least two cases were exposed to the same source. Statistically significant general source types were attributed by calculating the population attributable risk (analytical-comparative evidence). We identified an external source in 16 (14%) cases, and RDW as source in 28 (25%). Wearing inadequately disinfected dentures was the only RnDW source significantly associated with cases (OR = 3.2, 95% CI 1.3 to 7.8) and led to an additional 8% of cases with source attribution, for a total of 48% of cases attributed.

CONCLUSION

Using the appraisal matrix we attributed almost half of all cases of CALD to an infectious source, predominantly RDW. Risk for LD seems to be conferred primarily by the type of Legionella rather than the amount. Dentures as a new infectious source needs further, in particular, integrated microbiological, molecular and epidemiological confirmation.

Evaluation of a novel urinary antigen test kit for diagnosing Legionella pneumonia

OBJECTIVES

The aim of this study was to evaluate the diagnostic utility of a novel test kit that could theoretically detect all serogroups of Legionella pneumophila for diagnosing Legionella pneumonia, in comparison with existing kits.

METHODS

This study was conducted in 16 hospitals in Japan from April 2016 to December 2018. Three urinary antigen test kits were used: the novel kit (LAC-116), BinaxNOW Legionella (Binax), and Q-line Kyokutou Legionella (Q-line). In addition, sputum culture and nucleic acid detection tests and serum antibody tests were performed where possible. The diagnostic accuracy and correlations of the novel kit with the two existing kits were analyzed.

RESULTS

In total, 56 patients were diagnosed with Legionella pneumonia. The sensitivities of LAC-116, Binax, and Q-line were 79%, 84%, and 71%, respectively. The overall match rate between LAC-116 and Binax was 96.8% and between LAC-116 and Q-line was 96.4%. One patient had L. pneumophila serogroup 2, and only LAC-116 showed a positive result, whereas Binax and Q-line did not.

CONCLUSIONS

The novel Legionella urinary antigen test kit was useful for diagnosing Legionella pneumonia. In addition, it could detect Legionella pneumonia caused by non-L. pneumophila serogroup 1.

Structural study of the flagellar junction protein FlgL from Legionella pneumophila

Legionella pneumophila is a flagellated pathogenic bacterium that causes atypical pneumonia called Legionnaires' disease. The flagellum plays a key role in the pathogenesis of L. pneumophila in the host. The protein FlgL forms a junction between the flagellar hook and filament and has been reported to elicit the host humoral immune response. To provide structural insights into FlgL-mediated junction assembly and FlgL-based vaccine design, we performed structural and serological studies on L. pneumophila FlgL (lpFlgL). The crystal structure of a truncated lpFlgL protein that consists of the D1 and D2 domains was determined at 3.06 Å resolution. The D1 domain of lpFlgL adopts a primarily helical, rod-shaped structure, and the D2 domain folds into a β-sandwich structure that is affixed to the upper region of the D1 domain. The D1 domain of lpFlgL exhibits structural similarity to the flagellar filament protein flagellin, allowing us to propose a structural model of the lpFlgL junction based on the polymeric structure of flagellin. Furthermore, the D1 domain of lpFlgL exhibited substantially higher protein stability than the D2 domain and was responsible for most of the antigenicity of lpFlgL, suggesting that the D1 domain of lpFlgL would be a suitable target for the development of an anti-L. pneumophila vaccine.

Gasdermin-D and Caspase-7 are the key Caspase-1/8 substrates downstream of the NAIP5/NLRC4 inflammasome required for restriction of Legionella pneumophila

Inflammasomes are cytosolic multi-protein complexes that detect infection or cellular damage and activate the Caspase-1 (CASP1) protease. The NAIP5/NLRC4 inflammasome detects bacterial flagellin and is essential for resistance to the flagellated intracellular bacterium Legionella pneumophila. The effectors required downstream of NAIP5/NLRC4 to restrict bacterial replication remain unclear. Upon NAIP5/NLRC4 activation, CASP1 cleaves and activates the pore-forming protein Gasdermin-D (GSDMD) and the effector caspase-7 (CASP7). However, Casp1^–/– (and Casp1/11^–/–) mice are only partially susceptible to L. pneumophila and do not phenocopy Nlrc4^–/–mice, because NAIP5/NLRC4 also activates CASP8 for restriction of L. pneumophila infection. Here we show that CASP8 promotes the activation of CASP7 and that Casp7/1/11^–/– and Casp8/1/11^–/– mice recapitulate the full susceptibility of Nlrc4^–/– mice. Gsdmd^–/– mice exhibit only mild susceptibility to L. pneumophila, but Gsdmd^–/–Casp7^–/– mice are as susceptible as the Nlrc4^–/– mice. These results demonstrate that GSDMD and CASP7 are the key substrates downstream of NAIP5/NLRC4/CASP1/8 required for resistance to L. pneumophila.

Inflammasomes are multi-protein complexes that detect infection and other stimuli and activate the Caspase-1 (CASP1) protease. The effectors required downstream of NAIP5/NLRC4 to restrict bacterial replication remain unclear. Active CASP1 cleaves and activates the pore-forming protein gasdermin D (GSDMD) to induce inflammation and cell death. We have previously shown that CASP8 is activated by the NAIP5/NLRC4 inflammasome independently of CASP1 and functions to restrict replication of the intracellular bacterium Legionella pneumophila. Here, we show that CASP7 is activated downstream of CASP8 and is required for CASP8-dependent restriction of L. pneumophila replication in macrophages and in vivo. In addition, CASP7 is also activated by CASP1. Taken together, these results imply that CASP7 and GSDMD are the two key caspase substrates downstream of NAIP5/NLRC4. In support of this hypothesis, we found that mice double deficient in CASP7 and GSDMD are more susceptible than the single knockouts and are as susceptible as the Nlrc4 deficient mice for restriction of L. pneumophila replication in vivo. Collectively, our data indicate that GSDMD and CASP7 are activated by CASP1 and induce cell death and restriction of bacterial infection. Therefore, GSDMD and multiple caspases (CASP1, CASP7 and CASP8) operate downstream of the NAIP5/NLRC4 inflammasome for restriction of infection by pathogenic bacteria.

National Surveillance of Legionnaires' Disease, China, 2014-2016

We report national surveillance of Legionnaires' disease in China. Urine samples from 11 (3.85%) of 286 patients with severe pneumonia of unknown cause were positive for the Legionella pneumophila serogroup 1 antigen. We isolated Legionella strains from 7 patients. Improved diagnostic testing is needed for this underestimated disease in China.

Improvement of Legionnaires' disease diagnosis using real-time PCR assay: a retrospective analysis, Italy, 2010 to 2015

AimTo evaluate real-time PCR as a diagnostic method for Legionnaires' disease (LD). Detection of Legionella DNA is among the laboratory criteria of a probable LD case, according to the European Centre for Disease Prevention and Control, although the utility and advantages, as compared to culture, are widely recognised.MethodsTwo independent laboratories, one using an in-house and the other a commercial real-time PCR assay, analysed 354 respiratory samples from 311 patients hospitalised with pneumonia between 2010-15. The real-time PCR reliability was compared with that of culture and urinary antigen tests (UAT). Concordance, specificity, sensitivity and positive and negative predictive values (PPV and NPV, respectively) were calculated.ResultsOverall PCR detected eight additional LD cases, six of which were due to Legionella pneumophila (Lp) non-serogroup 1. The two real-time PCR assays were concordant in 99.4% of the samples. Considering in-house real-time PCR as the reference method, specificity of culture and UAT was 100% and 97.9% (95% CI: 96.2-99.6), while the sensitivity was 63.6% (95%CI: 58.6-68.6) and 77.8% (95% CI: 72.9-82.7). PPV and NPV for culture were 100% and 93.7% (95% CI: 91.2-96.3). PPV and NPV for UAT were 87.5% (95% CI: 83.6-91.4) and 95.8% (95% CI: 93.5-98.2).ConclusionRegardless of the real-time PCR assay used, it was possible to diagnose LD cases with higher sensitivity than using culture or UAT. These data encourage the adoption of PCR as routine laboratory testing to diagnose LD and such methods should be eligible to define a confirmed LD case.

Legionella pneumophila Serogroup 1 in the Water Facilities of a Tertiary Healthcare Center, India

Proactive environmental surveillance for Legionella pneumophila in hospitals that treat immunocompromised patients is a useful strategy for preventing nosocomial Legionnaires’ disease. We report the presence of L. pneumophila serogroup 1 in 15.2% of the water systems of our tertiary healthcare center, which should prompt health officials to formulate mitigation policies.

The common HAQ STING variant impairs cGAS-dependent antibacterial responses and is associated with susceptibility to Legionnaires' disease in humans

The cyclic GMP-AMP synthase (cGAS)-STING pathway is central for innate immune sensing of various bacterial, viral and protozoal infections. Recent studies identified the common HAQ and R232H alleles of TMEM173/STING, but the functional consequences of these variants for primary infections are unknown. Here we demonstrate that cGAS- and STING-deficient murine macrophages as well as human cells of individuals carrying HAQ TMEM173/STING were severely impaired in producing type I IFNs and pro-inflammatory cytokines in response to Legionella pneumophila, bacterial DNA or cyclic dinucleotides (CDNs). In contrast, R232H attenuated cytokine production only following stimulation with bacterial CDN, but not in response to L. pneumophila or DNA. In a mouse model of Legionnaires’ disease, cGAS- and STING-deficient animals exhibited higher bacterial loads as compared to wild-type mice. Moreover, the haplotype frequency of HAQ TMEM173/STING, but not of R232H TMEM173/STING, was increased in two independent cohorts of human Legionnaires’ disease patients as compared to healthy controls. Our study reveals that the cGAS-STING cascade contributes to antibacterial defense against L. pneumophila in mice and men, and provides important insight into how the common HAQ TMEM173/STING variant affects antimicrobial immune responses and susceptibility to infection.

Interferons (IFNs) and pro-inflammatory cytokines are key regulators of gene expression and antibacterial defense during Legionella pneumophila infection. Here we demonstrate that production of these mediators was largely or partly dependent on the cyclic GMP-AMP synthase (cGAS)-STING pathway in human and murine cells. Cells of individuals carrying the common HAQ allele of TMEM173/STING were strongly impaired in their ability to respond to L. pneumophila, bacterial DNA or cyclic dinucleotides (CDNs), whereas the R232H allele was only attenuated in sensing of exogenous CDNs. Importantly, cGAS and STING contributed to antibacterial defense in mice during L. pneumophila lung infection, and the allele frequency of HAQ TMEM173/STING, but not of R232H TMEM173/STING, was increased in two independent cohorts of human Legionnaires’ disease patients as compared to healthy controls. Hence, sensing of bacterial DNA by the cGAS/STING pathway contributes to antibacterial defense against L. pneumophila infection, and the hypomorphic variant HAQ TMEM173/STING is associated with increased susceptibility to Legionnaires’ disease in humans.

Street Cleaning Trucks as Potential Sources of Legionella pneumophila

In 2015, Legionnaires’ disease was diagnosed in a street cleaning worker. We found Legionella pneumophila serogroup 1 in the water and internal foam from the tanks of 2 trucks used by the worker during the incubation period. The internal foam was removed, and a Legionella prevention program was implemented.

Diagnostic testing for Legionnaires' disease

Legionnaires' disease is commonly diagnosed clinically using a urinary antigen test. The urinary antigen test is highly accurate for L. pneumophila serogroup 1, however other diagnostic tests should also be utilized in conjunction with the urinary antigen as many other Legionella species and serogroups are pathogenic. Culturing of patient specimens remains the gold standard for diagnosis of Legionnaires' disease. Selective media, BYCE with the addition of antibiotics, allows for a high sensitivity and specificity. Culturing can identify all species and serogroups of Legionella. A major benefit of culturing is that it provides the recovery of a patient isolate, which can be used to find an environmental match. Other diagnostic tests, including DFA and molecular tests such as PCR and LAMP, are useful tests to supplement culturing. Molecular tests provide much more rapid results in comparison to culture, however these tests should not be a primary diagnostic tool given their lower sensitivity and specificity in comparison to culturing. It is recommended that all laboratories develop the ability to culture patient specimens in-house with the selective media.

Human Anti-Lipopolysaccharid (LPS) antibodies against Legionella with high species specificity

Legionella are Gram-negative bacteria that are ubiquitously present in natural and man-made water reservoirs. When humans inhale aerosolized water contaminated with Legionella, alveolar macrophages can be infected, which may lead to a life-threatening pneumonia called Legionnaires' disease. Due to the universal distribution of Legionella in water and their potential threat to human health, the Legionella concentration in water for human use must be strictly monitored, which is difficult since the standard detection still relies on lengthy cultivation and analysis of bacterial morphology. In this study, an antibody against L. pneumophila has been generated from the naïve human HAL antibody libraries by phage-display for the first time. The panning was performed on whole bacterial cells in order to select antibodies that bind specifically to the cell surface of untreated Legionella. The bacterial cell wall component lipopolysaccharide (LPS) was identified as the target structure. Specific binding to the important pathogenic L. pneumophila strains Corby, Philadelphia-1 and Knoxville was observed, while no binding was detected to seven members of the families Enterobacteriaceae, Pseudomonadaceae or Clostridiaceae. Production of this antibody in the recombinant scFv-Fc format using either a murine or a human Fc part allowed the set-up of a sandwich-ELISA for detection of Legionella cells. The scFv-Fc construct proved to be very stable, even when stored for several weeks at elevated temperatures. A sensitivity limit of 4,000 cells was achieved. The scFv-Fc antibody pair was integrated on a biosensor, demonstrating the specific and fast detection of L. pneumophila on a portable device. With this system, 10,000 Legionella cells were detected within 35 min. Combined with a water filtration/concentration system, this antibody may be developed into a promising reagent for rapid on-site Legionella monitoring.

Occurrence of Legionella in showers at recreational facilities

Critical environments, including water systems in recreational settings, represent an important source of Legionella pneumophila infection in humans. In order to assess the potential risk for legionellosis, we analyzed Legionella contamination of water distribution systems in 36 recreational facilities equipped with swimming pools. One hundred and sixty water samples were analyzed from shower heads or taps located in locker rooms or in bathrooms. By culture method and polymerase chain reaction, 41/160 samples were positive for Legionella from 12/36 recreational centers. Hotels (57.1%) and sports centers (41.2%) were the most contaminated. L. pneumophila serotypes 2-14 (25/41) were more frequently found than serotype 1 (10/41). Samples at temperature ≥30 °C were more frequently positive than samples at temperature <30 °C (n = 39 vs n = 2, p < 0.00001). The presence of L. pneumophila was investigated by comparison with heterotrophic plate count (HPC), an indicator of water quality. The presence of L. pneumophila was associated more frequently with high and intermediate HPC load at 37 °C, therefore should be considered a potential source when HPC at 37 °C is >10 CFU/mL. Maintenance, good hygiene practices, interventions on the hydraulic system and regular controls must be implemented to minimize exposure to L. pneumophila infection risk.

The Influence of Programmed Cell Death in Myeloid Cells on Host Resilience to Infection with Legionella pneumophila or Streptococcus pyogenes

Pathogen clearance and host resilience/tolerance to infection are both important factors in surviving an infection. Cells of the myeloid lineage play important roles in both of these processes. Neutrophils, monocytes, macrophages, and dendritic cells all have important roles in initiation of the immune response and clearance of bacterial pathogens. If these cells are not properly regulated they can result in excessive inflammation and immunopathology leading to decreased host resilience. Programmed cell death (PCD) is one possible mechanism that myeloid cells may use to prevent excessive inflammation. Myeloid cell subsets play roles in tissue repair, immune response resolution, and maintenance of homeostasis, so excessive PCD may also influence host resilience in this way. In addition, myeloid cell death is one mechanism used to control pathogen replication and dissemination. Many of these functions for PCD have been well defined in vitro, but the role in vivo is less well understood. We created a mouse that constitutively expresses the pro-survival B-cell lymphoma (bcl)-2 protein in myeloid cells (CD68(bcl2tg), thus decreasing PCD specifically in myeloid cells. Using this mouse model we explored the impact that decreased cell death of these cells has on infection with two different bacterial pathogens, Legionella pneumophila and Streptococcus pyogenes. Both of these pathogens target multiple cell death pathways in myeloid cells, and the expression of bcl2 resulted in decreased PCD after infection. We examined both pathogen clearance and host resilience and found that myeloid cell death was crucial for host resilience. Surprisingly, the decreased myeloid PCD had minimal impact on pathogen clearance. These data indicate that the most important role of PCD during infection with these bacteria is to minimize inflammation and increase host resilience, not to aid in the clearance or prevent the spread of the pathogen.

Epigallocatechin Gallate Modulates Cytokine Production by Bone Marrow-Derived Dendritic Cells Stimulated with Lipopolysaccharide or Muramyldipeptide, or Infected with Legionella pneumophila

The primary polyphenol in green tea extract is the catechin epigallocatechin gallate (EGCG). Various studies have shown significant suppressive effects of catechin on mammalian cells, either tumor or normal cells, including lymphoid cells. Previous studies from this laboratory reported that EGCG has marked suppressive activity on murine macrophages infected with the intracellular bacterium Legionella pneumophila (Lp), an effect mediated by enhanced production of both tumor necrosis factor-α (TNF-α) and γ-interferon (IFN-γ). In the present study, primary murine bone marrow (BM)-derived dendritic cells (DCs), a phagocytic monocytic cell essential for innate immunity to intracellular microorganisms, such as Lp, were stimulated in vitro with the microbial stimulant lipopolysaccharide (LPS) from gram-negative bacteria, the cell wall component from gram-positive bacteria muramyldipeptide (MDP) or infected with Lp. Production of the T helper cell (Th1)-activating cytokine, interleukin-12 (IL-12) and the proinflammatory cytokine, tumor necrosis factor-α (TNF-α), produced mainly by phagocytic cells and important for antimicrobial immunity, was determined in cell culture supernatants by enzyme-linked immunosorbent assay (ELISA). Treatment of the cells with EGCG inhibited, in a dose-dependent manner, production of IL-12. In contrast, enhanced production of TNF-α occurred in a dose-dependent manner in the DC cultures stimulated with either soluble bacterial product or infected with Lp. Thus, the results of this study show that the EGCG catechin has a marked effect in modulating production of these immunoregulatory cytokines in stimulated DCs, which are important for antimicrobial immunity, especially innate immunity. Further studies are necessary to characterize the physiologic function of the effect of EGCG on TNF-α and IL-12 during Lp infection, and the mechanisms involved.

Molecular Typing of Legionella pneumophila Isolates in the Province of Quebec from 2005 to 2015

Legionella is found in natural and man-made aquatic environments, such as cooling towers and hot water plumbing infrastructures. Legionella pneumophila serogroup 1 (Lp1) is the most common etiological agent causing waterborne disease in the United States and Canada. This study reports the molecular characterization of Lp strains during a 10 year period. We conducted sequence-based typing (SBT) analysis on a large set of Lp isolates (n = 284) to investigate the province of Quebec sequence types (STs) distribution in order to identify dominant clusters. From 2005 to 2015, 181 clinical Lp isolates were typed by SBT (141 sporadic cases and 40 outbreak related cases). From the same period of time, 103 environmental isolates were also typed. Amongst the 108 sporadic cases of Lp1 typed, ST-62 was the most frequent (16.6%), followed by ST-213 (10.2%), ST-1 (8.3%) and ST-37 (8.3%). Amongst other serogroups (SG), ST-1327 (SG5) (27.3%) and ST-378 (SG10) (12.2%) were the most frequent. From the environmental isolates, ST-1 represent the more frequent SBT type (26.5%). Unweighted pair group method with arithmetic mean (UPGMA) dendrogram from the 108 sporadic cases of SG1 contains 4 major clusters (A to D) of related STs. Cluster B contains the majority of the strains (n = 61) and the three most frequent STs in our database (ST-62, ST-213 and ST-1). During the study period, we observed an important increase in the incidence rate in Quebec. All the community associated outbreaks, potentially or confirmed to be associated with a cooling tower were caused by Lp1 strains, by opposition to hospital associated outbreaks that were caused by serogroups of Lp other than SG1. The recent major Quebec City outbreak caused by ST-62, and the fact that this genotype is the most common in the province supports whole genome sequencing characterization of this particular sequence type in order to understand its evolution and associated virulence factors.

Clinical Characteristics of Legionella Pneumonia Diagnosed with Legionella Urinary Antigen Test

OBJECTIVE

The aim of our study was to describe the clinical characteristics of Legionella pneumonia diagnosed with a positive urinary antigen test, and factors associated with severe Legionella pneumonia were investigated.

METHODS

We retrospectively investigated the clinical characteristics of patients with Legionella pneumonia diagnosed at Tokai University Hospital between February 2006 and June 2012. The clinical characteristics of ICU cases and non-ICU cases were compared.

RESULTS

Twenty-six patients with Legionella pneumonia were identified (mean age 66.7 ± 19.3). Twenty patients were men (76.9 %). Impaired consciousness was observed in 12 patients (46.2 %), followed by gastrointestinal symptoms (38.5 %). Ten patients had severe pneumonia which required ICU admission. A case-controlled study comparing non-ICU cases and ICU cases demonstrated that cases with diabetes (OR 10.1, 95 % CI 1.1-90.5) and tachycardia (OR 10.1, 95 % CI 1.1-90.5) were significantly associated with ICU admission.

CONCLUSIONS

Legionella pneumonia did not always present as severe pneumonia. Extrapulmonary manifestations may be useful clues for diagnosis. Diabetic patients have not only a risk of contracting Legionella pneumonia, but also a risk of progression. Legionella pneumonia should be included in the differential diagnosis even in cases of mild to moderate pneumonia when presenting with extrapulmonary symptoms, especially in diabetic patients.

IFNs Modify the Proteome of Legionella-Containing Vacuoles and Restrict Infection Via IRG1-Derived Itaconic Acid

Macrophages can be niches for bacterial pathogens or antibacterial effector cells depending on the pathogen and signals from the immune system. Here we show that type I and II IFNs are master regulators of gene expression during Legionella pneumophila infection, and activators of an alveolar macrophage-intrinsic immune response that restricts bacterial growth during pneumonia. Quantitative mass spectrometry revealed that both IFNs substantially modify Legionella-containing vacuoles, and comparative analyses reveal distinct subsets of transcriptionally and spatially IFN-regulated proteins. Immune-responsive gene (IRG)1 is induced by IFNs in mitochondria that closely associate with Legionella-containing vacuoles, and mediates production of itaconic acid. This metabolite is bactericidal against intravacuolar L. pneumophila as well as extracellular multidrug-resistant Gram-positive and -negative bacteria. Our study explores the overall role IFNs play in inducing substantial remodeling of bacterial vacuoles and in stimulating production of IRG1-derived itaconic acid which targets intravacuolar pathogens. IRG1 or its product itaconic acid might be therapeutically targetable to fight intracellular and drug-resistant bacteria.

Numerous intracellular bacterial pathogens replicate in specialized vacuoles within macrophages. We systematically study the molecular mechanism and the impact of macrophage-intrinsic antibacterial defense. Using L. pneumophila, an important cause of pneumonia and model organism for intracellular bacteria, we found that type I and II interferons critically modify the proteome of bacterial vacuoles to restrict infection. We identify IRG1 and demonstrate a bactericidal activity of its metabolite itaconic acid on bacteria in their vacuole. Moreover, our study provides evidence for the impact of this cell-autonomous defense pathway in alveolar macrophages to restrict lung infection. We speculate that vacuolar IRG1 or its product itaconic acid could serve as future therapeutic targets to fight intracellular and drug-resistant bacteria.

[THE DIAGNOSTIC VALUE OF MODERN METHODS OF MICROBIOLOGICAL VERIFICATION OF COMMUNITY-ACQUIRED PNEUMONIA IN CLINICAL PRACTICE]

The study was carried out to determine etiological structure and informativeness of different methods of detection of agents of community-acquired pneumonia, the sampling included 274 examined patients aged from 16 to 80 years with community-acquired pneumonia of different degree of severity and being under hospital treatment. Besides of standard laboratory and clinical methods of examination ofpatients with community-acquired pneumonia special techniques of etiological verification were applied: molecular genetic analysis (polymerase chain reaction) of phlegm, qualitative detection of antigen Legionella pneumophila of serogroup 1 and antigen Streptococcus pneumoniae in samples of urine using quick immune chromatographic test, detection of level of serum specific immunoglobulines class M and G to Chlamidophilia pneumoniae, Mycoplasma pListeria monocytogenes in dynamics using immunoenzyme technique. The etiological structure of community-acquired pneumonia was established based of study results. The analysis of informativeness of different methods of etiological verification of diagnosis of community-acquired pneumonia demonstrated that combination ofpolymerase chain reaction and serological method is the optimal one.

An integrated passive-flow microfluidic biosensor with organic photodiodes for ultra-sensitive pathogen detection in water

This work reports on integrated passive-flow optical microfluidic devices to detect waterborne pathogens in the field. Ring-shaped organic photodiodes were integrated to a capillary-induced flow microfluidic channel for monitoring chemiluminescent sandwich immunoassays enhanced by gold nanoparticles. The integrated device yielded a resolution of 4×10(4) cells/mL for the detection of Legionella pneumophila, which represented a 25-fold improvement over chemiluminescence detection devices employing no gold-nanoparticle enhancement. This work demonstrates the feasibility of a low-cost but highly sensitive lab-on-a-chip device amenable for point-of-use applications.

The occurrence of antibodies against Legionella pneumophila in patients with autoimmune rheumatic diseases

INTRODUCTION

Patients with autoimmune rheumatic diseases are more susceptible to infection, owing to the underlying disease itself or to its treatment. Most commonly, infections affect the respiratory and urinary tracts. One of the etiological factors of infections in these patients is the bacteria of the genus Legionella.

OBJECTIVES

The aim of the study was to assess the prevalence of anti-Legionella pneumophila (L. pneumophila) antibodies in patients with autoimmune rheumatic diseases and to analyze individual and environmental risk factors for the development of Legionella infection in patients with positive antibody results.

PATIENTS AND METHODS

The study group consisted of 165 patients with autoimmune rheumatic diseases and 100 healthy subjects. Serum samples were tested for the presence of specific antibodies in the immunoglobulin (Ig) M and IgG classes against L. pneumophila serogroups 1 to 7 (SG 1-7) and the IgG class for serogroup 1 (SG 1).

RESULTS

Antibodies against L. pneumophila were found in 7 patients (4%): 5 cases with antibody positivity only in the IgG class and 2 cases with antibody positivity in both classes. In patients with positive IgG antibodies for SG 1-7, specific antibodies for L. pneumophila SG 1 were not detected. In the control group, positive results were obtained in 9 cases (9%): IgM positivity in 6 (6%) and IgG positivity in 3 (3%).

CONCLUSIONS

The frequency of antibodies to L. pneumophila in our patients is comparable to that in healthy individuals. L. pneumophila should be recognized as a potential pathogen in patients with autoimmune rheumatic diseases. Primary disease condition, immunosuppressive therapy, and other risk factors should not be ignored in these patients.

[Problems in the serological diagnosis of atypical pneumonia caused by Legionella pneumophila and Mycoplasma pneumoniae]

INTRODUCTION

The clinical presentation of atypical pneumonia is often similar to the presentation of more typical bacterial pneumonias and the etiological agent must be confirmed by laboratory diagnosis. This article will discuss the problems in the serological diagnosis of atypical pneumonia caused by Legionella pneumophila and Mycoplasma pneumoniae which are the agents most commonly associated with atypical pneumonia. Specifically, seeking the possibility of non-specific response, we evaluated the prevalence of antibodies to M. pneumoniae in serum samples obtained from patients suspected in clinical investigation for legionellosis.

METHODS

The total numbers of 261 serum obtained from patients suspected in clinical investigation for legionellosis, were tested by in-house ELISA with M. pneumoniae sonicated antigen. Some of the positive sera were also re-tested by western-blot with high specific recombinant M. pneumoniae P1 protein.

RESULTS

The diagnostic significant level of IgA antibodies to M. pneumoniae were diagnosed by ELISA in 71 (27,2%) of tested serum samples. Some of the IgA-positive sera have also high level of IgG and IgM antibodies to M pneumoniae (respectively 4,2% and 6,5%). Most from the 18 selected positive results obtained by ELISA were also confirmed by western-blot. It was characteristic that IgA antibodies to M pneumoniae were detected more than three times often in serum samples with positive serological tests for Legionnaires' disease than in samples with negative results for L. pneumophila.

CONCLUSIONS

This study showed the possibility of non-specific reactions in serological diagnosis of atypical pneumonia. However, according to the data of the literature, co-infections of L. pneumophila and M pneumoniae can not be excluded.

Alveolar macrophages and neutrophils are the primary reservoirs for Legionella pneumophila and mediate cytosolic surveillance of type IV secretion

Legionella pneumophila, an intracellular pathogen responsible for the severe pneumonia Legionnaires' disease, uses its dot/icm-encoded type IV secretion system (T4SS) to translocate effector proteins that promote its survival and replication into the host cell cytosol. However, by introducing bacterial products into the host cytosol, L. pneumophila also activates cytosolic immunosurveillance pathways, thereby triggering robust proinflammatory responses that mediate the control of infection. Thus, the pulmonary cell types that L. pneumophila infects not only may act as an intracellular niche that facilitates its pathogenesis but also may contribute to the immune response against L. pneumophila. The identity of these host cells remains poorly understood. Here, we developed a strain of L. pneumophila producing a fusion protein consisting of β-lactamase fused to the T4SS-translocated effector RalF, which allowed us to track cells injected by the T4SS. Our data reveal that alveolar macrophages and neutrophils both are the primary recipients of T4SS-translocated effectors and harbor viable L. pneumophila during pulmonary infection of mice. Moreover, both alveolar macrophages and neutrophils from infected mice produced tumor necrosis factor and interleukin-1α in response to T4SS-sufficient, but not T4SS-deficient, L. pneumophila. Collectively, our data suggest that alveolar macrophages and neutrophils are both an intracellular reservoir for L. pneumophila and a source of proinflammatory cytokines that contribute to the host immune response against L. pneumophila during pulmonary infection.

The frustrated host response to Legionella pneumophila is bypassed by MyD88-dependent translation of pro-inflammatory cytokines

Many pathogens, particularly those that require their host for survival, have devised mechanisms to subvert the host immune response in order to survive and replicate intracellularly. Legionella pneumophila, the causative agent of Legionnaires' disease, promotes intracellular growth by translocating proteins into its host cytosol through its type IV protein secretion machinery. At least 5 of the bacterial translocated effectors interfere with the function of host cell elongation factors, blocking translation and causing the induction of a unique host cell transcriptional profile. In addition, L. pneumophila also interferes with translation initiation, by preventing cap-dependent translation in host cells. We demonstrate here that protein translation inhibition by L. pneumophila leads to a frustrated host MAP kinase response, where genes involved in the pathway are transcribed but fail to be translated due to the bacterium-induced protein synthesis inhibition. Surprisingly, few pro-inflammatory cytokines, such as IL-1α and IL-1β, bypass this inhibition and get synthesized in the presence of Legionella effectors. We show that the selective synthesis of these genes requires MyD88 signaling and takes place in both infected cells that harbor bacteria and neighboring bystander cells. Our findings offer a perspective of how host cells are able to cope with pathogen-encoded activities that disrupt normal cellular process and initiate a successful inflammatory response.

Translation inhibition is a common virulence mechanism used by a number of pathogens (e.g. Diphtheria Toxin, Shiga Toxin and Pseudomonas Exotoxin A). It has been a mystery how host cells mount a pathogen-specific response and clear infection under conditions where protein synthesis is blocked by pathogens. Using Legionella pneumophila as a model, a bacterium that efficiently blocks the host protein translation machinery, we show here that the innate immune system has devised a mechanism to cope with translation inhibition by selectively synthesizing proteins that are required for inflammation.

The machinery at endoplasmic reticulum-plasma membrane contact sites contributes to spatial regulation of multiple Legionella effector proteins

The Dot/Icm system of the intracellular pathogen Legionella pneumophila has the capacity to deliver over 270 effector proteins into host cells during infection. Important questions remain as to spatial and temporal mechanisms used to regulate such a large array of virulence determinants after they have been delivered into host cells. Here we investigated several L. pneumophila effector proteins that contain a conserved phosphatidylinositol-4-phosphate (PI4P)-binding domain first described in the effector DrrA (SidM). This PI4P binding domain was essential for the localization of effectors to the early L. pneumophila-containing vacuole (LCV), and DrrA-mediated recruitment of Rab1 to the LCV required PI4P-binding activity. It was found that the host cell machinery that regulates sites of contact between the plasma membrane (PM) and the endoplasmic reticulum (ER) modulates PI4P dynamics on the LCV to control localization of these effectors. Specifically, phosphatidylinositol-4-kinase IIIα (PI4KIIIα) was important for generating a PI4P signature that enabled L. pneumophila effectors to localize to the PM-derived vacuole, and the ER-associated phosphatase Sac1 was involved in metabolizing the PI4P on the vacuole to promote the dissociation of effectors. A defect in L. pneumophila replication in macrophages deficient in PI4KIIIα was observed, highlighting that a PM-derived PI4P signature is critical for biogenesis of a vacuole that supports intracellular multiplication of L. pneumophila. These data indicate that PI4P metabolism by enzymes controlling PM-ER contact sites regulate the association of L. pneumophila effectors to coordinate early stages of vacuole biogenesis.

The intracellular pathogen Legionella pneumophila encodes at least 270 effectors that modulate trafficking of the pathogen-occupied vacuole. The mechanisms by which effectors are controlled in host cells are of key interest. Spatial and temporal regulation of effector function has been proposed to involve effector binding to host phosphoinositides. We present results showing that L. pneumophila utilizes the host kinase PI4KIIIα to generate PI4P on the bacterial vacuole and this signature mediates the localization of DrrA and subsequent recruitment of the GTPase Rab1. Additionally, it was found that the host PI4P phosphatase Sac1 was involved in consuming PI4P on the vacuole, which reduced DrrA-mediated recruitment of Rab1 to the LCV. Our data supports the recent concept that PI4KIIIα is important for generation of the plasma-membrane pool of PI4P in host cells, and demonstrates a functional consequence for PI4P-binding by an L. pneumophila effector protein.

SQSTM1/p62/A170 regulates the severity of Legionella pneumophila pneumonia by modulating inflammasome activity

Sequestosome1/A170/p62 (SQSTM1) is a scaffold multifunctional protein involved in several cellular events, such as signal transduction, cell survival, cell death, and inflammation. SQSTM1 expression by macrophages is induced in response to environmental stresses; however, its role in macrophage-mediated host responses to environmental stimuli, such as infectious pathogens, remains unclear. In this study, we investigated the role of SQSTM1 in host responses to Legionella pneumophila, an intra-cellular pathogen that infects macrophages, in both an SQSTM1-deficient (SQSTM1(-/-) ) mouse model and macrophages from these mice. Compared with wild-type (WT) macrophages, the production and secretion of the proinflammatory cytokine IL-1β was significantly enhanced in SQSTM1(-/-) macrophages after infection with L. pneumophila. Inflammasome activity, indicated by the level of IL-18 and caspase-1 activity, was also elevated in SQSTM1(-/-) macrophages after infection with L. pneumophila. SQSTM1 may interact with nucleotide-binding oligomerization domain-like receptor family, caspase recruitment domain-containing 4 and nucleotide-binding oligomerization domain like receptor family, pyrin domain containing 3 proteins to inhibit their self-dimerization. Acute pulmonary inflammation induced by L. pneumophila and silica was enhanced in SQSTM1(-/-) mice with an increase in IL-1β levels in the bronchoalveolar lavage fluids. These findings suggest that SQSTM1 is a negative regulator of acute pulmonary inflammation, possibly by regulating inflammasome activity and subsequent proinflammatory cytokine production.

TREM-1 deficiency can attenuate disease severity without affecting pathogen clearance

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune reactions. While TREM-1-amplified responses likely aid an improved detection and elimination of pathogens, excessive production of cytokines and oxygen radicals can also severely harm the host. Studies addressing the pathogenic role of TREM-1 during endotoxin-induced shock or microbial sepsis have so far mostly relied on the administration of TREM-1 fusion proteins or peptides representing part of the extracellular domain of TREM-1. However, binding of these agents to the yet unidentified TREM-1 ligand could also impact signaling through alternative receptors. More importantly, controversial results have been obtained regarding the requirement of TREM-1 for microbial control. To unambiguously investigate the role of TREM-1 in homeostasis and disease, we have generated mice deficient in Trem1. Trem1^−/− mice are viable, fertile and show no altered hematopoietic compartment. In CD4⁺ T cell- and dextran sodium sulfate-induced models of colitis, Trem1^−/− mice displayed significantly attenuated disease that was associated with reduced inflammatory infiltrates and diminished expression of pro-inflammatory cytokines. Trem1^−/− mice also exhibited reduced neutrophilic infiltration and decreased lesion size upon infection with Leishmania major. Furthermore, reduced morbidity was observed for influenza virus-infected Trem1^−/− mice. Importantly, while immune-associated pathologies were significantly reduced, Trem1^−/− mice were equally capable of controlling infections with L. major, influenza virus, but also Legionella pneumophila as Trem1^+/+ controls. Our results not only demonstrate an unanticipated pathogenic impact of TREM-1 during a viral and parasitic infection, but also indicate that therapeutic blocking of TREM-1 in distinct inflammatory disorders holds considerable promise by blunting excessive inflammation while preserving the capacity for microbial control.

Triggering receptor expressed on myeloid cells-1 (TREM-1) is an immune receptor expressed by myeloid cells that has the capacity to augment pro-inflammatory responses in the context of a microbial infection. While a TREM-1-amplified response likely serves the efficient clearance of pathogens, it also bears the potential to cause substantial tissue damage or even death. Hence, TREM-1 appears a possible therapeutic target for tempering deleterious host-pathogen interactions. However, in models of bacterial sepsis controversial findings have been obtained regarding the requirement of TREM-1 for bacterial control - depending on the overall degree of the TREM-1 blockade that was achieved. In order to conclusively investigate harmful versus essential functions of TREM-1 in vivo, we have generated mice deficient in Trem1. Trem1^−/− mice were subjected to experimentally-induced intestinal inflammation (as a model of a non-infectious, yet microbial-driven disease) and also analysed following infections with Leishmania major, influenza virus and Legionella pneumophila. Across all models analysed, Trem1^−/− mice showed substantially reduced immune-associated disease. We thus describe a previously unanticipated pathogenic role for TREM-1 also during a parasitic and viral infection. Importantly, our data suggest that in certain diseases microbial control can be achieved in the context of blunted inflammation in the absence of TREM-1.

Patients' age and the dynamics of IgM for L. pneumophila sg1

MATERIAL AND METHODS

The results of IgM L. pneumophila sg1 test in 304 adults and 270 children performed at NIPH-NIH in 2004-2007 were analyzed to determine the effects of patients' age and the interval between collected sera on the results and the interpretation.

RESULTS

Significant difference in the level of IgM, depending on the age of the patients (P0 = 0.0084) was found. Positive results (in total 20.4% of patients) were the most frequently observed in patients aged 19-29 years (42.5%), and the least--in patients 60 y.o. and < 2 y.o. (7%). Average and median levels of IgM in these two groups (+60 y.o. and < 2 y.o.) were similar and significantly different from the results in the other groups. From 44 adults and 33 children > or = 2 sera were collected. There was a significant difference in the interval between collecting the first and second serum sample in adults (mainly 3-5 weeks) and children (mainly 2-4 weeks). Significant increase of IgM levels was observed in children when the interval between 1 and 2 sample didn't exceed 4 weeks, while in adults this change was also observed at > 5 weeks (25% of patients). No significant differences in the analysis of the IgM ratio in children (1.25-14) and adults (1.5-26) was found, but longer persistence of IgM in adults than in children was observed.

CONCLUSIONS

Demonstrated trend of faster decline in the level of IgM among children than in adults indicated that in suspected case of legionellosis in children, the serum sample should be taken up to 4-5 weeks after the onset, and at intervals of 1-2 weeks maximum.

Interferon-Gamma Reverses the Evasion ofBirc1e/Naip5Gene Mediated Murine Macrophage Immunity byLegionella pneumophilaMutant Lacking Flagellin

Legionella pneumophila is the etiologic agent of Legionnaires' disease. This bacterium contains a single monopolar flagellum, of which the FlaA subunit is a major protein constituent. The murine macrophage resistance against this bacterium is controlled by the Birc1e/Naip5 gene, which belongs to the NOD family. We evaluated the intracellular growth of the flaA mutant bacteria as well as another aflagellated fliA mutant, within bone marrow-derived macrophages from mice with an intact (C57BL/6, BALB/c) or mutated (A/J) Birc1e/Naip5 gene. The flaA mutant L. pneumophila multiplied within C57BL/6 and BALB/c macrophages while the wild-type strain did not. Cell viability was not impaired until 3 days after infection when the flaA mutant bacteria replicated 10(2-3)-fold in macrophages, implying that L. pneumophila inhibited host cell death during the early phase of intracellular replication. The addition of recombinant interferon-gamma (IFN-gamma) to the infected macrophages restricted replication of the flaA mutant within macrophages; these treated cells also showed enhanced nitric oxide production, although inhibition of nitric oxide production did not affect the IFN-gamma induced inhibition of Legionella replication. These findings suggested that IFN-gamma activated macrophages to restrict the intracellular growth of the L. pneumophila flaA mutant by a NO independent pathway.

Activation of Ran GTPase by a Legionella effector promotes microtubule polymerization, pathogen vacuole motility and infection

The causative agent of Legionnaires' disease, Legionella pneumophila, uses the Icm/Dot type IV secretion system (T4SS) to form in phagocytes a distinct "Legionella-containing vacuole" (LCV), which intercepts endosomal and secretory vesicle trafficking. Proteomics revealed the presence of the small GTPase Ran and its effector RanBP1 on purified LCVs. Here we validate that Ran and RanBP1 localize to LCVs and promote intracellular growth of L. pneumophila. Moreover, the L. pneumophila protein LegG1, which contains putative RCC1 Ran guanine nucleotide exchange factor (GEF) domains, accumulates on LCVs in an Icm/Dot-dependent manner. L. pneumophila wild-type bacteria, but not strains lacking LegG1 or a functional Icm/Dot T4SS, activate Ran on LCVs, while purified LegG1 produces active Ran(GTP) in cell lysates. L. pneumophila lacking legG1 is compromised for intracellular growth in macrophages and amoebae, yet is as cytotoxic as the wild-type strain. A downstream effect of LegG1 is to stabilize microtubules, as revealed by conventional and stimulated emission depletion (STED) fluorescence microscopy, subcellular fractionation and Western blot, or by microbial microinjection through the T3SS of a Yersinia strain lacking endogenous effectors. Real-time fluorescence imaging indicates that LCVs harboring wild-type L. pneumophila rapidly move along microtubules, while LCVs harboring ΔlegG1 mutant bacteria are stalled. Together, our results demonstrate that Ran activation and RanBP1 promote LCV formation, and the Icm/Dot substrate LegG1 functions as a bacterial Ran activator, which localizes to LCVs and promotes microtubule stabilization, LCV motility as well as intracellular replication of L. pneumophila.

Comparative Genomics Reveal That Host-Innate Immune Responses Influence the Clinical Prevalence of Legionella pneumophila Serogroups

Legionella pneumophila is the primary etiologic agent of legionellosis, a potentially fatal respiratory illness. Amongst the sixteen described L. pneumophila serogroups, a majority of the clinical infections diagnosed using standard methods are serogroup 1 (Sg1). This high clinical prevalence of Sg1 is hypothesized to be linked to environmental specific advantages and/or to increased virulence of strains belonging to Sg1. The genetic determinants for this prevalence remain unknown primarily due to the limited genomic information available for non-Sg1 clinical strains. Through a systematic attempt to culture Legionella from patient respiratory samples, we have previously reported that 34% of all culture confirmed legionellosis cases in Ontario (n = 351) are caused by non-Sg1 Legionella. Phylogenetic analysis combining multiple-locus variable number tandem repeat analysis and sequence based typing profiles of all non-Sg1 identified that L. pneumophila clinical strains (n = 73) belonging to the two most prevalent molecular types were Sg6. We conducted whole genome sequencing of two strains representative of these sequence types and one distant neighbour. Comparative genomics of the three L. pneumophila Sg6 genomes reported here with published L. pneumophila serogroup 1 genomes identified genetic differences in the O-antigen biosynthetic cluster. Comparative optical mapping analysis between Sg6 and Sg1 further corroborated this finding. We confirmed an altered O-antigen profile of Sg6, and tested its possible effects on growth and replication in in vitro biological models and experimental murine infections. Our data indicates that while clinical Sg1 might not be better suited than Sg6 in colonizing environmental niches, increased bloodstream dissemination through resistance to the alternative pathway of complement mediated killing in the human host may explain its higher prevalence.

[Expression and purification of Legionella pneumophila MIP protein and its application in serological diagnosis]

OBJECTIVE

To express and purify macrophage infectivity potentiator (MIP) protein of Legionella pneumophila(Lp), and explore its value in the serological diagnosis of Lp.

METHODS

The recombinant plasmid pET-mip was transformed into E.coli BL21 competent cells. The expression of MIP protein was induced, and then analyzed by SDS-PAGE electrophoresis, purified by affinity chromatography. We screened out 40 positive blood serum and 30 negative blood serum using the DRG (Germany, IgG/IgM/IgA) Lp kit. The blood serum samples were detected for IgG, IgM, IgA antibody levels by indirect ELISA that we had established with the purified MIP protein as the coating antigen, as well as by R&D (USA, IgG/IgM/IgA) Lp kit. The two methods were compared in the sensitivity, specificity and consistency of the test results.

RESULTS

The recombinant MIP protein was successfully expressed and purified with Mr; being 40 000 in E.coli BL21. In comparison of the indirect ELISA we developed with the R&D Lp kit for detecting Lp antibody IgG, IgM and IgA in blood serum, the specificity of IgG was 88.5% and the sensitivity was 95.5%, the Kappa value was 0.846 (P<0.05), the area under the ROC curve was 0.927; the specificity of IgM was 89.3% and the sensitivity was 97.6%, the Kappa value was 0.88 (P<0.05), the area under the ROC curve was 0.947; the specificity of IgA was 90% and the sensitivity was 95.2%, the Kappa value was 0.856 (P<0.05), the area under the ROC curve was 0.931.

CONCLUSION

MIP proteins of L.pneumophila was expressed and purified successfully, and MIP protein can be used as a coating antigen in serological diagnosis of L.pneumophila.

Legionella pneumonia cases over a five-year period: a descriptive, retrospective study of outcomes in a UK district hospital

As the recent outbreaks in Edinburgh and Camarthen, UK, have shown, Legionella pneumonia (LP) remains a significant public health problem, which is not only confined to those who have travelled abroad. In both outbreaks and sporadic cases, diagnosis can go unrecognised. We reviewed the demographics, comorbidities, diagnosis, treatment and clinical outcome of LP cases over five years in a district general hospital in northwest England. Over half of LP cases were UK acquired and 'classic' clinical features were common. Clinical criteria for diagnosing LP were confirmed, but few sputum samples were sent to reference laboratories, limiting further essential epidemiological mapping of UK cases. Following current UK community-acquired pneumonia guidance would have missed nearly one quarter of LP cases in our series, potentially leading to further morbidity and mortality.

In vitro derivation of macrophage from guinea pig bone marrow with human M-CSF

The guinea pig has a storied history as a model in the study of infectious disease and immunology. Because of reproducibility of data and availability of various reagents, inbred mice have since supplanted the guinea pig as the animal model-of-choice in these fields. However, several clinically-significant microorganisms do not cause the same pathology in mice, or mice may not be susceptible to these infections. These demonstrate the utility of other animal models - either as the primary method to study a particular infection, or to confirm or refute findings in the mouse before translating basic science into clinical practice. The mononuclear phagocyte, or macrophage (Mφ), plays a key role in antigen presentation and the pathogenesis of intracellular bacteria, such as Mycobacterium tuberculosis and Legionella pneumophila. Because of variable yield and difficult extraction from tissue, the preferred method of producing Mφ for in vitro studies is to expand murine bone marrow (BM) precursors with mouse macrophage colony-stimulating factor (M-CSF). This has not been shown in the guinea pig. Here, we report the empiric observation that human M-CSF - but not mouse M-CSF, nor human granulocyte/macrophage colony-stimulating factor - can be used to induce BM precursor differentiation into bonafide Mφ. The differentiated cells appeared as enlarged adherent cells, capable of both pinocytosis and large particle phagocytosis. Furthermore, we showed that these guinea pig BM-derived Mφ, similar to human monocyte/Mφ lines but unlike most murine BM Mφ, support growth of wild type L. pneumophila. This method may prove useful for in vitro studies of Mφ in the guinea pig, as well as in the translation of results found using mouse BM-derived Mφ towards studies in human immunology and infectious disease.

[The development of polymer immunoglobulin preparations to identify different serovars legionella pneumophilia in reaction of slide-agglutination]

The article deals with the results of study targeted to develop polymer diagnostic preparation to identify epidemically significant serogroups Legionella pneumophilia. The preparation combines rate of record (1-5 min) of reaction of paragglutinining preparations with color visualization and demonstrative of reaction of volume agglomeration with polymer diagnosticums. The specially synthesized polymer microspheres were sensibilized with serums enriched with antibodies to lipopolysaccharide of corresponding serovar L. pneumophilia. The derived immunoglobulin diagnostic preparations detect agent of legionellesis in the reaction of slide-agglutination on glass during 1-5 min. The polymer diagnostic preparations provide positive reaction with culture of corresponding serovar and no reaction with other gomologic and geterologic agents of infectious diseases.

[Relevance of the detection of Streptococcus pneumoniae antigen in human urine in the diagnosis of lower respiratory tract infections]

BACKGROUND AND OBJECTIVE

Techniques membrane antigen immunochromatographic detecting in urine the pneumococcal polysaccharide C, have developed significantly, increasing requests for antigenuria to clinical microbiology laboratories. We evaluated the impact of the application of this test in the diagnosis of infections of lower respiratory tract.

PATIENTS AND METHOD

Six hundred and sixteen determinations were performed by antigenuria BinaxNOW(®) S. pneumoniae in as many patients over 14 years admitted to the Hospital Universitario Virgen de las Nieves (Granada) between November 2010 and March 2011.

RESULTS

In 91.1% of patients who were determined antigenuria the presence of respiratory symptoms justified the request. Only 8.4% of 616 antigenurias performed were positive. S. pneumoniae was isolated from the respiratory sample culture in 8 of these 52 patients. In 29.8% of patients the diagnosis of lower respiratory tract infection was based on clinical, radiological and/or analytical, as antigenurias were negative and did not involve any other additional microbiological test.

CONCLUSIONS

We believe that this technique should be used in a complementary manner, and never to the detriment of other microbiological tests, especially in hospitalized patients.

Typing methods for legionella

In this chapter we describe the methods currently used for subgrouping Legionella pneumophila and other non-pneumophila species. In the first part we describe monoclonal antibody (mAb) subgrouping, either by indirect immunofluorescence or indirect ELISA methods. These monoclonal antibodies are not commercially available but can be obtained for noncommercial purposes from one of the authors. Further, we describe pulsed-field gel electrophoresis (PFGE), amplified fragment length polymorphism (AFLP) and sequence-based typing (SBT) as well standardized and reproducible methods for genotyping. The SBT schema is currently available for L. pneumophila whereas PFGE and AFLP can be used for all Legionella species. For certain applications it might be useful to use spoligotyping to distinguish strains belonging to the same sequence type (ST).

[Serologic characteristic of Legionella pneumophila strains isolated from potentially dangerous water systems in Russian Federation in 2007 - 2011]

AIM

Study serologic diversity of Legionella pneumophila strains circulating in potentially dangerous water systems in Russian Federation by using an international panel of monoclonal antibodies.

MATERIALS AND METHODS

Serotyping of 234 L. pneumophila strains isolated from coolers of industrial facilities and systems of hot water supply in Russian Federation in 2007 - 2011 was performed by enzyme immunoassay by using an international panel of monoclonal antibodies.

RESULTS

Membership of the isolated strains in 14 L. pneumophila serogroups and in 7 subgroups of serogroup 1 was established. Among the isolated cultures serogroup 1 and 6, and Oxford and Heysham subgroup strains were predominant. L. pneumophila serogroup 1 strains were predominant in cooler water, and serogroup 6--in the hot water supply systems. 7 L. pneumophila strains of the serogroup 1 were typed by monoclone MAb 3/1 associated with LPS epitope that is characteristic for the most epidemically significant legionella strains.

CONCLUSION

Typing by using international panel of monoclonal antibodies for characteristic and evaluation of epidemical significance of legionella strains being isolated form potentially dangerous water systems is the most informative and methodically accessible to a wide range of biological laboratories.

[The lethiferous journey of a bacterium--the research progress of secretion systems and effectors in Legionella pneumophila]

Legionella pneumophila is the intracellular bacterial pathogen that causes severe Legionnaires' disease and flu-like Pontiac fever. To accomplish successful aggression against hosts, L. pneumophila secrets more than 150 kinds of substrate effector proteins into host cells via its Type IVB secretion system. With the multiple functions of effectors, L. pneumophila evades effectively the defense systems of hosts, converts or adjusts intracellular vesicular transport of hosts, modifies or disguises its Legionella containing vacuole (LCV), modulates the cell cycle program and inhibits the apoptosis of host cells, and finally gains the comfortable intracellular replicative niche. Effectors can also help L. pneumophila escape from hosts cells after completing the proliferation.. L. pneumophila has became the distinct model for pathogen-host interaction research, and its secretion systems as well as the substrate effectors are attracting more and more attentions. Researching on T4BSS and effectors could not only help investigate the pathogenesis of intracellular bacterial pathogens, but also promote the comprehension about innate immune responses of hosts. This article reviews the progresses of L. pneumophila T4BSS and effectors, trying to demonstrate to the readers the cunning survival strategy and the delicate virulent machine of L. pneumophila.

[Legionella pneumonia in a patient with positive culture results of Legionella pneumophila serotype 1 from bronchoalveolar lavage fluid but negative urinary antigen test results]

A 39-year-old man presented to a local physician complaining of fever, headache without cough or sputum. Abnormal shadows were found on chest X-ray films. Pneumonia was diagnosed and he was referred to our hospital, where chest computed tomography showed bilateral, multifocal, and patchy ground-glass opacities. Neither the urinary antigen test for Streptococcus pneumoniae nor that for Legionella was positive. Because he had visited a public spa several days before developing the fever and headache, and because hypophosphatemia was identified, we then suspected Legionella pneumonia. Bronchoalveolar lavage fluid yielded positive culture of Legionella pneumophila serotype 1. The Legionella urinary antigen is known to detect Legionella pneumophila serotype 1 infection; however, sensitivity and specificity of the test are 60-95% and > 99%, but care should be taken when urinary antigen test results are negative in suspected cases of Legionella pneumophila serotype 1 pneumonia. In the present case, bronchoalveolar lavage fluid was a useful method for diagnosing Legionella pneumonia.

Multifaceted effects of synthetic TLR2 ligand and Legionella pneumophilia on Treg-mediated suppression of T cell activation

BACKGROUND

Regulatory T cells (Treg) play a crucial role in maintaining immune homeostasis and self-tolerance. The immune suppressive effects of Tregs should however be limited in case effective immunity is required against pathogens or cancer cells. We previously found that the Toll-like receptor 2 (TLR2) agonist, Pam3CysSK4, directly stimulated Tregs to expand and temporarily abrogate their suppressive capabilities. In this study, we evaluate the effect of Pam3CysSK4 and Legionella pneumophila, a natural TLR2 containing infectious agent, on effector T (Teff) cells and dendritic cells (DCs) individually and in co-cultures with Tregs.

RESULTS

TLR2 agonists can directly provide a co-stimulatory signal inducing enhanced proliferation and cytokine production of naive CD4+ Teff cells. With respect to cytokine production, DCs appear to be most sensitive to low amounts of TLR agonists. Using wild type and TLR2-deficient cells in Treg suppression assays, we accordingly show that all cells (e.g. Treg, Teff cells and DCs) contributed to overcome Treg-mediated suppression of Teff cell proliferation. Furthermore, while TLR2-stimulated Tregs readily lost their ability to suppress Teff cell proliferation, cytokine production by Teff cells was still suppressed. Similar results were obtained upon stimulation with TLR2 ligand containing bacteria, Legionella pneumophila.

CONCLUSIONS

These findings indicate that both synthetic and natural TLR2 agonists affect DCs, Teff cells and Treg directly, resulting in multi-modal modulation of Treg-mediated suppression of Teff cells. Moreover, Treg-mediated suppression of Teff cell proliferation is functionally distinct from suppression of cytokine secretion.

Secreted bacterial effectors that inhibit host protein synthesis are critical for induction of the innate immune response to virulent Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila causes an inflammatory pneumonia called Legionnaires' Disease. For virulence, L. pneumophila requires a Dot/Icm type IV secretion system that translocates bacterial effectors to the host cytosol. L. pneumophila lacking the Dot/Icm system is recognized by Toll-like receptors (TLRs), leading to a canonical NF-κB-dependent transcriptional response. In addition, L. pneumophila expressing a functional Dot/Icm system potently induces unique transcriptional targets, including proinflammatory genes such as Il23a and Csf2. Here we demonstrate that this Dot/Icm-dependent response, which we term the effector-triggered response (ETR), requires five translocated bacterial effectors that inhibit host protein synthesis. Upon infection of macrophages with virulent L. pneumophila, these five effectors caused a global decrease in host translation, thereby preventing synthesis of IκB, an inhibitor of the NF-κB transcription factor. Thus, macrophages infected with wildtype L. pneumophila exhibited prolonged activation of NF-κB, which was associated with transcription of ETR target genes such as Il23a and Csf2. L. pneumophila mutants lacking the five effectors still activated TLRs and NF-κB, but because the mutants permitted normal IκB synthesis, NF-κB activation was more transient and was not sufficient to fully induce the ETR. L. pneumophila mutants expressing enzymatically inactive effectors were also unable to fully induce the ETR, whereas multiple compounds or bacterial toxins that inhibit host protein synthesis via distinct mechanisms recapitulated the ETR when administered with TLR ligands. Previous studies have demonstrated that the host response to bacterial infection is induced primarily by specific microbial molecules that activate TLRs or cytosolic pattern recognition receptors. Our results add to this model by providing a striking illustration of how the host immune response to a virulent pathogen can also be shaped by pathogen-encoded activities, such as inhibition of host protein synthesis.

[Comparison and evaluation of the Binax EIA and Biotest EIA urinary antigen kits for detection of Legionella pneumophila antigen in urine samples]

The Binax and the Biotest urinary antigen kits for detection of L. pneumophila antigen were compared by testing of selected 67 urine samples obtained from EWGLI as reference samples in External Quality Assessment Scheme. Thirty nine were positive with the Binax kit (100% of sensitivity), and 33 were positive with the Biotest (84.6% of sensitivity). The test specificities were 100% for the both kits. It was concluded that the Binax kit was more suitable for the routine diagnosis of Legionella infections than the Biotest kit.

Isolation and identification of Legionella pneumophila from material reclamation facilities

Sampling points at a material reclamation facility (MRF) were monitored over three months for the presence of Legionella spp. A number of different Legionellae were isolated and typed to identify L. pneumophila serogroup 1, the serotype which is the most common human pathogen. Phenotypic methods resulted in a total of 61 presumptive isolates of Legionella spp. Using latex agglutination, 26 out of the 61 were identified as L. pneumophila serogroup 1, 23 as L. pneumophila serogroups 2-14, and the remaining 12 were Legionella spp. However, on typing using pulse field gel electrophoresis, the 26 L. pneumophila serotype 1 isolates were a diverse group of 25 PFGE types with none persisting in the environment over time. This diversity suggests that there are a number of contamination sources for this important human pathogen in the MRF environment which constitute a risk to health for operatives in these facilities.