IL-33 controls IL-22-dependent antibacterial defense by modulating the microbiota.

IL-22 plays a critical role in defending against mucosal infections, but how IL-22 production is regulated is incompletely understood. Here, we show that mice lacking IL-33 or its receptor ST2 (IL-1RL1) were more resistant to Streptococcus pneumoniae lung infection than wild-type animals and that single-nucleotide polymorphisms in IL33 and IL1RL1 were associated with pneumococcal pneumonia in humans. The effect of IL-33 on S. pneumoniae infection was mediated by negative regulation of IL-22 production in innate lymphoid cells (ILCs) but independent of ILC2s as well as IL-4 and IL-13 signaling. Moreover, IL-33's influence on IL-22-dependent antibacterial defense was dependent on housing conditions of the mice and mediated by IL-33's modulatory effect on the gut microbiota. Collectively, we provide insight into the bidirectional crosstalk between the innate immune system and the microbiota. We conclude that both genetic and environmental factors influence the gut microbiota, thereby impacting the efficacy of antibacterial immune defense and susceptibility to pneumonia.

Post-resolution macrophages shape long-term tissue immunity and integrity in a mouse model of pneumococcal pneumonia.

Resolving inflammation is thought to return the affected tissue back to homoeostasis but recent evidence supports a non-linear model of resolution involving a phase of prolonged immune activity. Here we show that within days following resolution of Streptococcus pneumoniae-triggered lung inflammation, there is an influx of antigen specific lymphocytes with a memory and tissue-resident phenotype as well as macrophages bearing alveolar or interstitial phenotype. The transcriptome of these macrophages shows enrichment of genes associated with prostaglandin biosynthesis and genes that drive T cell chemotaxis and differentiation. Therapeutic depletion of post-resolution macrophages, inhibition of prostaglandin E2 (PGE2) synthesis or treatment with an EP4 antagonist, MF498, reduce numbers of lung CD4+/CD44+/CD62L+ and CD4+/CD44+/CD62L-/CD27+ T cells as well as their expression of the α-integrin, CD103. The T cells fail to reappear and reactivate upon secondary challenge for up to six weeks following primary infection. Concomitantly, EP4 antagonism through MF498 causes accumulation of lung macrophages and marked tissue fibrosis. Our study thus shows that PGE2 signalling, predominantly via EP4, plays an important role during the second wave of immune activity following resolution of inflammation. This secondary immune activation drives local tissue-resident T cell development while limiting tissue injury.

High-resolution genomics identifies pneumococcal diversity and persistence of vaccine types in children with community-acquired pneumonia in the UK and Ireland.

BACKGROUND: Streptococcus pneumoniae is a global cause of community-acquired pneumonia (CAP) and invasive disease in children. The CAP-IT trial (grant No. 13/88/11; https://www.capitstudy.org.uk/ ) collected nasopharyngeal swabs from children discharged from hospitals with clinically diagnosed CAP, and found no differences in pneumococci susceptibility between higher and lower antibiotic doses and shorter and longer durations of oral amoxicillin treatment. Here, we studied in-depth the genomic epidemiology of pneumococcal (vaccine) serotypes and their antibiotic resistance profiles. METHODS: Three-hundred and ninety pneumococci cultured from 1132 nasopharyngeal swabs from 718 children were whole-genome sequenced (Illumina) and tested for susceptibility to penicillin and amoxicillin. Genome heterogeneity analysis was performed using long-read sequenced isolates (PacBio, n = 10) and publicly available sequences. RESULTS: Among 390 unique pneumococcal isolates, serotypes 15B/C, 11 A, 15 A and 23B1 were most prevalent (n = 145, 37.2%). PCV13 serotypes 3, 19A, and 19F were also identified (n = 25, 6.4%). STs associated with 19A and 19F demonstrated high genome variability, in contrast to serotype 3 (n = 13, 3.3%) that remained highly stable over a 20-year period. Non-susceptibility to penicillin (n = 61, 15.6%) and amoxicillin (n = 10, 2.6%) was low among the pneumococci analysed here and was independent of treatment dosage and duration. However, all 23B1 isolates (n = 27, 6.9%) were penicillin non-susceptible. This serotype was also identified in ST177, which is historically associated with the PCV13 serotype 19F and penicillin susceptibility, indicating a potential capsule-switch event. CONCLUSIONS: Our data suggest that amoxicillin use does not drive pneumococcal serotype prevalence among children in the UK, and prompts consideration of PCVs with additional serotype coverage that are likely to further decrease CAP in this target population. Genotype 23B1 represents the convergence of a non-vaccine genotype with penicillin non-susceptibility and might provide a persistence strategy for ST types historically associated with vaccine serotypes. This highlights the need for continued genomic surveillance.

CETP inhibition enhances monocyte activation and bacterial clearance and reduces streptococcus pneumonia-associated mortality in mice.

Sepsis is a leading cause of mortality worldwide, and pneumonia is the most common cause of sepsis in humans. Low levels of high-density lipoprotein cholesterol (HDL-C) levels are associated with an increased risk of death from sepsis, and increasing levels of HDL-C by inhibition of cholesteryl ester transfer protein (CETP) decreases mortality from intraabdominal polymicrobial sepsis in APOE*3-Leiden.CETP mice. Here, we show that treatment with the CETP inhibitor (CETPi) anacetrapib reduced mortality from Streptococcus pneumoniae-induced sepsis in APOE*3-Leiden.CETP and APOA1.CETP mice. Mechanistically, CETP inhibition reduced the host proinflammatory response via attenuation of proinflammatory cytokine transcription and release. This effect was dependent on the presence of HDL, leading to attenuation of immune-mediated organ damage. In addition, CETP inhibition promoted monocyte activation in the blood prior to the onset of sepsis, resulting in accelerated macrophage recruitment to the lung and liver. In vitro experiments demonstrated that CETP inhibition significantly promoted the activation of proinflammatory signaling in peripheral blood mononuclear cells and THP1 cells in the absence of HDL; this may represent a mechanism responsible for improved bacterial clearance during sepsis. These findings provide evidence that CETP inhibition represents a potential approach to reduce mortality from pneumosepsis.

Clinical and economic burden of invasive pneumococcal disease and noninvasive all-cause pneumonia in hospitalized US adults: A multicenter analysis from 2015 to 2020.

OBJECTIVES: To evaluate the clinical and economic outcomes in adults hospitalized with invasive pneumococcal disease (IPD) and noninvasive all-cause pneumonia (ACP) overall and by antimicrobial resistance (AMR) status. METHODS: Hospitalized adults from the BD Insights Research Database with an ICD10 code for IPD, noninvasive ACP or a positive Streptococcus pneumoniae culture/urine antigen test were included. Descriptive statistics and multivariable analyses were used to evaluate outcomes (in-hospital mortality, length of stay [LOS], cost per admission, and hospital margin [costs - payments]). RESULTS: The study included 88,182 adult patients at 90 US hospitals (October 2015-February 2020). Most (98.6%) had noninvasive ACP and 40.2% were <65 years old. Of 1450 culture-positive patients, 37.7% had an isolate resistant to ≥1 antibiotic class. Observed mortality, median LOS, cost per admission, and hospital margins were 8.3%, 6 days, $9791, and $11, respectively. Risk factors for mortality included ≥50 years of age, higher risk of pneumococcal disease (based on chronic or immunocompromising conditions), and intensive care unit admission. Patients with IPD had similar mortality rates and hospital margins compared with noninvasive ACP, but greater costs per admission and LOS. CONCLUSION: IPD and noninvasive ACP are associated with substantial clinical and economic burden across all adult age groups. Expanded pneumococcal vaccination programs may help reduce disease burden and decrease hospital costs.

Invasive disease caused simultaneously by two different serotypes of Streptococcus pneumoniae: a microbiological appreciation.

We report a clinical case of a child with an invasive pneumococcal disease caused by two different pneumococcal serotypes that belonged to different sequence types. She was a 15-month-old girl with pneumonia and pleural effusion in which S. pneumoniae colonies with different morphologies grew, one from the blood culture (characteristic greyish appearance) and the other from the pleural fluid (mucoid appearance). The isolate from blood was serotype 22 F (ST698/CC698/GPSC61), while the isolate from the pleural fluid was serotype 3 (ST180/CC180/GPSC12). The patient fully recovered after treatment with intravenous ampicillin followed by oral amoxicillin.

Chronic ethanol exposure impairs alveolar leukocyte infiltration during pneumococcal pneumonia, leading to an increased bacterial burden despite increased CXCL1 and nitric oxide levels.

Ethanol abuse is a risk factor for the development of pneumonia caused by Streptococcus pneumoniae, a critical pathogen for public health. The aim of this article was to investigate the inflammatory mechanisms involved in pneumococcal pneumonia that may be associated with chronic ethanol exposure. Male C57BL6/J-Unib mice were exposed to 20% (v/v) ethanol for twelve weeks and intranasally infected with 5x104 CFU of S. pneumoniae. Twenty-four hours after infection, lungs, bronchoalveolar lavage and blood samples were obtained to assess the consequences of chronic ethanol exposure during infection. Alcohol-fed mice showed increased production of nitric oxide and CXCL1 in alveoli and plasma during pneumococcal pneumonia. Beside this, ethanol-treated mice exhibited a decrease in leukocyte infiltration into the alveoli and reduced frequency of severe lung inflammation, which was associated with an increase in bacterial load. Curiously, no changes were observed in survival after infection. Taken together, these results demonstrate that chronic ethanol exposure alters the inflammatory response during S. pneumoniae lung infection in mice with a reduction in the inflammatory infiltrate even in the presence of higher levels of the chemoattractant CXCL1.

MicroRNA-223 Dampens Pulmonary Inflammation during Pneumococcal Pneumonia.

Community-acquired pneumonia remains a major contributor to global communicable disease-mediated mortality. Neutrophils play a leading role in trying to contain bacterial lung infection, but they also drive detrimental pulmonary inflammation, when dysregulated. Here we aimed at understanding the role of microRNA-223 in orchestrating pulmonary inflammation during pneumococcal pneumonia. Serum microRNA-223 was measured in patients with pneumococcal pneumonia and in healthy subjects. Pulmonary inflammation in wild-type and microRNA-223-knockout mice was assessed in terms of disease course, histopathology, cellular recruitment and evaluation of inflammatory protein and gene signatures following pneumococcal infection. Low levels of serum microRNA-223 correlated with increased disease severity in pneumococcal pneumonia patients. Prolonged neutrophilic influx into the lungs and alveolar spaces was detected in pneumococci-infected microRNA-223-knockout mice, possibly accounting for aggravated histopathology and acute lung injury. Expression of microRNA-223 in wild-type mice was induced by pneumococcal infection in a time-dependent manner in whole lungs and lung neutrophils. Single-cell transcriptome analyses of murine lungs revealed a unique profile of antimicrobial and cellular maturation genes that are dysregulated in neutrophils lacking microRNA-223. Taken together, low levels of microRNA-223 in human pneumonia patient serum were associated with increased disease severity, whilst its absence provoked dysregulation of the neutrophil transcriptome in murine pneumococcal pneumonia.

Protective role of Cav-1 in pneumolysin-induced endothelial barrier dysfunction.

Pneumolysin (PLY) is a bacterial pore forming toxin and primary virulence factor of Streptococcus pneumonia, a major cause of pneumonia. PLY binds cholesterol-rich domains of the endothelial cell (EC) plasma membrane resulting in pore assembly and increased intracellular (IC) Ca2+ levels that compromise endothelial barrier integrity. Caveolae are specialized plasmalemma microdomains of ECs enriched in cholesterol. We hypothesized that the abundance of cholesterol-rich domains in EC plasma membranes confers cellular susceptibility to PLY. Contrary to this hypothesis, we found increased PLY-induced IC Ca2+ following membrane cholesterol depletion. Caveolin-1 (Cav-1) is an essential structural protein of caveolae and its regulation by cholesterol levels suggested a possible role in EC barrier function. Indeed, Cav-1 and its scaffolding domain peptide protected the endothelial barrier from PLY-induced disruption. In loss of function experiments, Cav-1 was knocked-out using CRISPR-Cas9 or silenced in human lung microvascular ECs. Loss of Cav-1 significantly enhanced the ability of PLY to disrupt endothelial barrier integrity. Rescue experiments with re-expression of Cav-1 or its scaffolding domain peptide protected the EC barrier against PLY-induced barrier disruption. Dynamin-2 (DNM2) is known to regulate caveolar membrane endocytosis. Inhibition of endocytosis, with dynamin inhibitors or siDNM2 amplified PLY induced EC barrier dysfunction. These results suggest that Cav-1 protects the endothelial barrier against PLY by promoting endocytosis of damaged membrane, thus reducing calcium entry and PLY-dependent signaling.

Pneumococcal urinary antigen testing for antimicrobial guidance in community-acquired pneumonia-A register-based cohort study.

OBJECTIVES: To evaluate the effect of pneumococcal urinary antigen test (UAT) usage on broad-spectrum antibiotic treatment in community-acquired pneumonia (CAP). METHODS: Patients admitted to 32 Swedish hospitals between 2011 and 2014 were retrospectively included from the Swedish National Quality Register of CAP. Using propensity score matched data, stratified by CRB-65 score, we studied the effect of performing UAT and of positive test results on treatment with broad-spectrum ß-lactam monotherapy (BSBM) and antibiotics with coverage for atypical bacteria compared to narrow-spectrum ß-lactam monotherapy (NSBM). RESULTS: UAT was performed for 4,995/14,590 (34.2%) patients, 603/4,995 (12.1%) of whom had positive test results. At day three, performing UAT was not associated with decreased use of BSBM (OR 1.07, 95% CI 0.94-1.23) but was associated with increased atypical coverage among patients with CRB-65 score 2 (OR 1.47, 95% CI 1.06-2.02). A positive UAT was associated with decreased BSBM use (OR 0.39, 95% CI 0.25-0.60) and decreased atypical coverage (OR 0.25, 95% CI 0.16-0.37), predominantly in non-severe CAP. At day one, performing UAT was associated with atypical coverage among patients with CRB-65 scores 2 (OR 2.60, 95% CI 1.69-3.98) and 3-4 (OR 3.69, 95% CI 1.55-8.79), and a positive test reduced the odds of BSBM treatment among CRB-65 score 3-4 patients (OR 3.49, 95% CI 1.02-12.0). CONCLUSIONS: Performing UAT had no overall effect on decreasing the use of BSBM treatment by day three of hospitalization, yet non-severely ill patients with positive UAT results were less likely to be treated with BSBM and antibiotics with atypical coverage.

Staphylococcus aureus Community-acquired Pneumonia in Children After 13-Valent Pneumococcal Vaccination (2008-2018): Epidemiology, Clinical Characteristics and Outcomes.

BACKGROUND: The epidemiology of community-acquired pneumonia (CAP) has changed, influenced by sociosanitary conditions and vaccination status. We aimed to analyze the recent epidemiology of bacterial CAP in hospitalized children in a setting with high pneumococcal vaccination coverage and to describe the clinical characteristics of pediatric Staphylococcus aureus CAP. METHODS: Children <17 years old hospitalized from 2008 to 2018 with bacterial CAP in 5 tertiary hospitals in Spain were included. Cases with pneumococcal CAP were randomly selected as comparative group following a case-control ratio of 2:1 with S. aureus CAP. RESULTS: A total of 313 bacterial CAP were diagnosed: Streptococcus pneumoniae CAP (n = 236, 75.4%), Streptococcus pyogenes CAP (n = 43, 13.7%) and S. aureus CAP (n = 34, 10.9%). Throughout the study period, the prevalence of S. pyogenes increased (annual percentage change: +16.1% [95% CI: 1.7-32.4], P = 0.031), S. pneumoniae decreased (annual percentage change: -4.4% [95 CI: -8.8 to 0.2], P = 0.057) and S. aureus remained stable. Nine isolates of S. aureus (26.5%) were methicillin-resistant. Seventeen cases (50%) with S. aureus CAP had some pulmonary complication and 21 (61.7%) required intensive care. S. pneumoniae CAP showed a trend toward higher prevalence of pulmonary complications compared with S. aureus CAP (69.1% vs. 50.0%, P = 0.060), including higher frequency of pulmonary necrosis (32.4% vs. 5.9%, P = 0.003). CONCLUSIONS: The incidence of S. aureus CAP in children remained stable, whereas the prevalence of pneumococcal CAP decreased and S. pyogenes CAP increased. Patients with S. aureus presented a high frequency of severe outcomes, but a lower risk of pulmonary complications than patients with S. pneumoniae.

TBK1 Is Required for Host Defense Functions Distinct from Type I IFN Expression and Myeloid Cell Recruitment in Murine Streptococcus pneumoniae Pneumonia.

Bacterial pneumonia induces the rapid recruitment and activation of neutrophils and macrophages into the lung, and these cells contribute to bacterial clearance and other defense functions. TBK1 (TANK-binding kinase 1) performs many functions, including activation of the type I IFN pathway and regulation of autophagy and mitophagy, but its contribution to antibacterial defenses in the lung is unclear. We previously showed that lung neutrophils upregulate mRNAs for TBK1 and its accessory proteins during Streptococcus pneumoniae pneumonia, despite low or absent expression of type I IFN in these cells. We hypothesized that TBK1 performs key antibacterial functions in pneumonia apart from type I IFN expression. Using TBK1 null mice, we show that TBK1 contributes to antibacterial defenses and promotes bacterial clearance and survival. TBK1 null mice express lower concentrations of many cytokines in the infected lung. Conditional deletion of TBK1 with LysMCre results in TBK1 deletion from macrophages but not neutrophils. LysMCre TBK1 mice have no defect in cytokine expression, implicating a nonmacrophage cell type as a key TBK1-dependent cell. TBK1 null neutrophils have no defect in recruitment to the infected lung but show impaired activation of p65/NF-κB and STAT1 and lower expression of reactive oxygen species, IFNγ, and IL12p40. TLR1/2 and 4 agonists each induce phosphorylation of TBK1 in neutrophils. Surprisingly, neutrophil TBK1 activation in vivo does not require the adaptor STING. Thus, TBK1 is a critical component of STING-independent antibacterial responses in the lung, and TBK1 is necessary for multiple neutrophil functions.

ZIP8-Mediated Intestinal Dysbiosis Impairs Pulmonary Host Defense against Bacterial Pneumonia.

Pneumococcal pneumonia is a leading cause of morbidity and mortality worldwide. An increased susceptibility is due, in part, to compromised immune function. Zinc is required for proper immune function, and an insufficient dietary intake increases the risk of pneumonia. Our group was the first to reveal that the Zn transporter, ZIP8, is required for host defense. Furthermore, the gut microbiota that is essential for lung immunity is adversely impacted by a commonly occurring defective ZIP8 allele in humans. Taken together, we hypothesized that loss of the ZIP8 function would lead to intestinal dysbiosis and impaired host defense against pneumonia. To test this, we utilized a novel myeloid-specific Zip8KO mouse model in our studies. The comparison of the cecal microbial composition of wild-type and Zip8KO mice revealed significant differences in microbial community structure. Most strikingly, upon a S. pneumoniae lung infection, mice recolonized with Zip8KO-derived microbiota exhibited an increase in weight loss, bacterial dissemination, and lung inflammation compared to mice recolonized with WT microbiota. For the first time, we reveal the critical role of myeloid-specific ZIP8 on the maintenance of the gut microbiome structure, and that loss of ZIP8 leads to intestinal dysbiosis and impaired host defense in the lung. Given the high incidence of dietary Zn deficiency and the ZIP8 variant allele in the human population, additional investigation is warranted to improve surveillance and treatment strategies.

Rapid identification of pathogens associated with ventilator-associated pneumonia by Nanopore sequencing.

BACKGROUND: Aetiology detection is crucial in the diagnosis and treatment of ventilator-associated pneumonia (VAP). However, the detection method needs improvement. In this study, we used Nanopore sequencing to build a quick detection protocol and compared the efficiency of different methods for detecting 7 VAP pathogens. METHODS: The endotracheal aspirate (ETA) of 83 patients with suspected VAP from Peking University Third Hospital (PUTH) was collected, saponins were used to deplete host genomes, and PCR- or non-PCR-amplified library construction methods were used and compared. Sequence was performed with MinION equipment and local data analysis methods were used for sequencing and data analysis. RESULTS: Saponin depletion effectively removed 11 of 12 human genomes, while most pathogenic bacterial genome results showed no significant difference except for S. pneumoniae. Moreover, the average sequence time decreased from 19.6 h to 3.62 h. The non-PCR amplification method and PCR amplification method for library build has a similar average sensitivity (85.8% vs. 86.35%), but the non-PCR amplification method has a better average specificity (100% VS 91.15%), and required less time. The whole method takes 5-6 h from ETA extraction to pathogen classification. After analysing the 7 pathogens enrolled in our study, the average sensitivity of metagenomic sequencing was approximately 2.4 times higher than that of clinical culture (89.15% vs. 37.77%), and the average specificity was 98.8%. CONCLUSIONS: Using saponins to remove the human genome and a non-PCR amplification method to build libraries can be used for the identification of pathogens in the ETA of VAP patients within 6 h by MinION, which provides a new approach for the rapid identification of pathogens in clinical departments.

Porphyromonas gingivalis Components/Secretions Synergistically Enhance Pneumonia Caused by Streptococcus pneumoniae in Mice.

Streptococcus pneumoniae is an important causative organism of respiratory tract infections. Although periodontal bacteria have been shown to influence respiratory infections such as aspiration pneumonia, the synergistic effect of S. pneumoniae and Porphyromonas gingivalis, a periodontopathic bacterium, on pneumococcal infections is unclear. To investigate whether P. gingivalis accelerates pneumococcal infections, we tested the effects of inoculating P. gingivalis culture supernatant (PgSup) into S. pneumoniae-infected mice. Mice were intratracheally injected with S. pneumoniae and PgSup to induce pneumonia, and lung histopathological sections and the absolute number and frequency of neutrophils and macrophages in the lung were analyzed. Proinflammatory cytokine/chemokine expression was examined by qPCR and ELISA. Inflammatory cell infiltration was observed in S. pneumoniae-infected mice and S. pnemoniae and PgSup mixed-infected mice, and mixed-infected mice showed more pronounced inflammation in lung. The ratios of monocytes/macrophages and neutrophils were not significantly different between the lungs of S. pneumoniae-infected mice and those of mixed-infected mice. PgSup synergistically increased TNF-α expression/production and IL-17 production compared with S. pneumoniae infection alone. We demonstrated that PgSup enhanced inflammation in pneumonia caused by S. pneumoniae, suggesting that virulence factors produced by P. gingivalis are involved in the exacerbation of respiratory tract infections such as aspiration pneumonia.

Host Stress Signals Stimulate Pneumococcal Transition from Colonization to Dissemination into the Lungs.

Streptococcus pneumoniae is an asymptomatic colonizer of the nasopharynx, but it is also one of the most important bacterial pathogens of humans, causing a wide range of mild to life-threatening diseases. The basis of the pneumococcal transition from a commensal to a parasitic lifestyle is not fully understood. We hypothesize that exposure to host catecholamine stress hormones is important for this transition. In this study, we demonstrated that pneumococci preexposed to a hormone released during stress, norepinephrine (NE), have an increased capacity to translocate from the nasopharynx into the lungs compared to untreated pneumococci. Examination of NE-treated pneumococci revealed major alterations in metabolic profiles, cell associations, capsule synthesis, and cell size. By systemically mutating all 12 two-component and 1 orphan regulatory systems, we also identified a unique genetic regulatory circuit involved in pneumococcal recognition and responsiveness to human stress hormones. IMPORTANCE Microbes acquire unique lifestyles under different environmental conditions. Although this is a widespread occurrence, our knowledge of the importance of various host signals and their impact on microbial behavior is not clear despite the therapeutic value of this knowledge. We discovered that catecholamine stress hormones are the host signals that trigger the passage of Streptococcus pneumoniae from a commensal to a parasitic state. We identify that stress hormone treatment of this microbe leads to reductions in cell size and capsule synthesis and renders it more able to migrate from the nasopharynx into the lungs in a mouse model of infection. The microbe requires the TCS09 protein for the recognition and processing of stress hormone signals. Our work has particular clinical significance as catecholamines are abundant in upper respiratory fluids as well as being administered therapeutically to reduce inflammation in ventilated patients, which may explain why intubation in the critically ill is a recognized risk factor for the development of pneumococcal pneumonia.

Splenic macrophages as the source of bacteraemia during pneumococcal pneumonia.

BACKGROUND: Severe community-acquired pneumococcal pneumonia is commonly associated with bacteraemia. Although it is assumed that the bacteraemia solely derives from pneumococci entering the blood from the lungs it is unknown if other organs are important in the pathogenesis of bacteraemia. Using three models, we tested the relevance of the spleen in pneumonia-associated bacteraemia. METHODS: We used human spleens perfused ex vivo to explore permissiveness to bacterial replication, a non-human primate model to check for splenic involvement during pneumonia and a mouse pneumonia-bacteraemia model to demonstrate that splenic involvement correlates with invasive disease. FINDINGS: Here we present evidence that the spleen is the reservoir of bacteraemia during pneumonia. We found that in the human spleen infected with pneumococci, clusters with increasing number of bacteria were detectable within macrophages. These clusters also were detected in non-human primates. When intranasally infected mice were treated with a non-therapeutic dose of azithromycin, which had no effect on pneumonia but concentrated inside splenic macrophages, bacteria were absent from the spleen and blood and importantly mice had no signs of disease. INTERPRETATION: We conclude that the bacterial load in the spleen, and not lung, correlates with the occurrence of bacteraemia. This supports the hypothesis that the spleen, and not the lungs, is the major source of bacteria during systemic infection associated with pneumococcal pneumonia; a finding that provides a mechanistic basis for using combination therapies including macrolides in the treatment of severe community-acquired pneumococcal pneumonia. FUNDING: Oxford University, Wolfson Foundation, MRC, NIH, NIHR, and MRC and BBSRC studentships supported the work.

Inosine monophosphate and inosine differentially regulate endotoxemia and bacterial sepsis.

Inosine monophosphate (IMP) is the intracellular precursor for both adenosine monophosphate and guanosine monophosphate and thus plays a central role in intracellular purine metabolism. IMP can also serve as an extracellular signaling molecule, and can regulate diverse processes such as taste sensation, neutrophil function, and ischemia-reperfusion injury. How IMP regulates inflammation induced by bacterial products or bacteria is unknown. In this study, we demonstrate that IMP suppressed tumor necrosis factor (TNF)-α production and augmented IL-10 production in endotoxemic mice. IMP exerted its effects through metabolism to inosine, as IMP only suppressed TNF-α following its CD73-mediated degradation to inosine in lipopolysaccharide-activated macrophages. Studies with gene targeted mice and pharmacological antagonism indicated that A2A , A2B, and A3 adenosine receptors are not required for the inosine suppression of TNF-α production. The inosine suppression of TNF-α production did not require its metabolism to hypoxanthine through purine nucleoside phosphorylase or its uptake into cells through concentrative nucleoside transporters indicating a role for alternative metabolic/uptake pathways. Inosine augmented IL-ß production by macrophages in which inflammasome was activated by lipopolysaccharide and ATP. In contrast to its effects in endotoxemia, IMP failed to affect the inflammatory response to abdominal sepsis and pneumonia. We conclude that extracellular IMP and inosine differentially regulate the inflammatory response.

Predicting Oral Beta-lactam susceptibilities against Streptococcus pneumoniae.

BACKGROUND: Oral beta-lactam antimicrobials are not routinely tested against Streptococcus pneumoniae due to presumed susceptibility based upon penicillin minimum inhibitory concentration (MIC) testing. Currently, Clinical and Laboratory Standards Institute provides comments to use penicillin MIC ≤0.06 to predict oral cephalosporin susceptibility. However, no guidance is provided when cefotaxime MIC is known, leading to uncertainty with interpretation. The purpose of this study was to evaluate cefotaxime and penicillin MICs and their respective correlation to oral beta-lactam categorical susceptibility patterns. METHODS: 249 S. pneumoniae isolates were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF) and then tested by broth microdilution method to penicillin, cefotaxime, amoxicillin, cefdinir, cefpodoxime, and cefuroxime. RESULTS: Using Clinical and Laboratory Standards Institute (CLSI) non-meningitis breakpoints for cefotaxime, 240/249 isolates were classified as susceptible. Of the cefotaxime susceptible isolates, 23% of the isolates are misrepresented as cefdinir susceptible. Amoxicillin correlated well with penicillin MIC breakpoints with only 1 discordant isolate out of 249. CONCLUSION: The correlation between amoxicillin and penicillin creates a very reliable predictor to determine categorical susceptibility. However oral cephalosporins were not well predicted by either penicillin or cefotaxime leading to the possible risk of treatment failures. Caution should be used when transitioning to oral cephalosporins in cefotaxime susceptible isolates, especially with higher cefotaxime MICs.

Lung-resident memory B cells protect against bacterial pneumonia.

Lung-resident memory B cells (BRM cells) are elicited after influenza infections of mice, but connections to other pathogens and hosts - as well as their functional significance - have yet to be determined. We postulate that BRM cells are core components of lung immunity. To test this, we examined whether lung BRM cells are elicited by the respiratory pathogen pneumococcus, are present in humans, and are important in pneumonia defense. Lungs of mice that had recovered from pneumococcal infections did not contain organized tertiary lymphoid organs, but did have plasma cells and noncirculating memory B cells. The latter expressed distinctive surface markers (including CD69, PD-L2, CD80, and CD73) and were poised to secrete antibodies upon stimulation. Human lungs also contained B cells with a resident memory phenotype. In mice recovered from pneumococcal pneumonia, depletion of PD-L2+ B cells, including lung BRM cells, diminished bacterial clearance and the level of pneumococcus-reactive antibodies in the lung. These data define lung BRM cells as a common feature of pathogen-experienced lungs and provide direct evidence of a role for these cells in pulmonary antibacterial immunity.