IL-17 can be protective or deleterious in murine pneumococcal pneumonia.

Streptococcus pneumoniae is the major bacterial cause of community-acquired pneumonia, and the leading agent of childhood pneumonia deaths worldwide. Nasal colonization is an essential step prior to infection. The cytokine IL-17 protects against such colonization and vaccines that enhance IL-17 responses to pneumococcal colonization are being developed. The role of IL-17 in host defence against pneumonia is not known. To address this issue, we have utilized a murine model of pneumococcal pneumonia in which the gene for the IL-17 cytokine family receptor, Il17ra, has been inactivated. Using this model, we show that IL-17 produced predominantly from γδ T cells protects mice against death from the invasive TIGR4 strain (serotype 4) which expresses a relatively thin capsule. However, in pneumonia produced by two heavily encapsulated strains with low invasive potential (serotypes 3 and 6B), IL-17 significantly enhanced mortality. Neutrophil uptake and killing of the serotype 3 strain was significantly impaired compared to the serotype 4 strain and depletion of neutrophils with antibody enhanced survival of mice infected with the highly encapsulated SRL1 strain. These data strongly suggest that IL-17 mediated neutrophil recruitment to the lungs clears infection from the invasive TIGR4 strain but that lung neutrophils exacerbate disease caused by the highly encapsulated pneumococcal strains. Thus, whilst augmenting IL-17 immune responses against pneumococci may decrease nasal colonization, this may worsen outcome during pneumonia caused by some strains.

IL-17 signalling restructures the nasal microbiome and drives dynamic changes following Streptococcus pneumoniae colonization.

BACKGROUND: The bacterial pathogen Streptococcus pneumoniae colonizes the nasopharynx prior to causing disease, necessitating successful competition with the resident microflora. Cytokines of the IL-17 family are important in host defence against this pathogen but their effect on the nasopharyngeal microbiome is unknown. Here we analyse the influence of IL-17 on the composition and interactions of the nasopharyngeal microbiome before and after pneumococcal colonization. RESULTS: Using a murine model and 16S rRNA profiling, we found that a lack of IL-17 signalling led to profound alterations in the nasal but not lung microbiome characterized by decreased diversity and richness, increases in Proteobacteria and reduction in Bacteroidetes, Actinobacteria and Acidobacteria. Following experimental pneumococcal nasal inoculation, animals lacking IL-17 family signalling showed increased pneumococcal colonization, though both wild type and knockout animals showed as significant disruption of nasal microbiome composition, with increases in the proportion of Proteobacteria, even in animals that did not have persistent colonization. Sparse correlation analysis of the composition of the microbiome at various time points after infection showed strong positive interactions within the Firmicutes and Proteobacteria, but strong antagonism between members of these two phyla. CONCLUSIONS: These results show the powerful influence of IL-17 signalling on the composition of the nasal microbiome before and after pneumococcal colonization, and apparent lack of interspecific competition between pneumococci and other Firmicutes. IL-17 driven changes in nasal microbiome composition may thus be an important factor in successful resistance to pneumococcal colonization and potentially could be manipulated to augment host defence against this pathogen.

Late Ebola virus relapse causing meningoencephalitis: a case report.

BACKGROUND: There are thousands of survivors of the 2014 Ebola outbreak in west Africa. Ebola virus can persist in survivors for months in immune-privileged sites; however, viral relapse causing life-threatening and potentially transmissible disease has not been described. We report a case of late relapse in a patient who had been treated for severe Ebola virus disease with high viral load (peak cycle threshold value 13.2). METHODS: A 39-year-old female nurse from Scotland, who had assisted the humanitarian effort in Sierra Leone, had received intensive supportive treatment and experimental antiviral therapies, and had been discharged with undetectable Ebola virus RNA in peripheral blood. The patient was readmitted to hospital 9 months after discharge with symptoms of acute meningitis, and was found to have Ebola virus in cerebrospinal fluid (CSF). She was treated with supportive therapy and experimental antiviral drug GS-5734 (Gilead Sciences, San Francisco, Foster City, CA, USA). We monitored Ebola virus RNA in CSF and plasma, and sequenced the viral genome using an unbiased metagenomic approach. FINDINGS: On admission, reverse transcriptase PCR identified Ebola virus RNA at a higher level in CSF (cycle threshold value 23.7) than plasma (31.3); infectious virus was only recovered from CSF. The patient developed progressive meningoencephalitis with cranial neuropathies and radiculopathy. Clinical recovery was associated with addition of high-dose corticosteroids during GS-5734 treatment. CSF Ebola virus RNA slowly declined and was undetectable following 14 days of treatment with GS-5734. Sequencing of plasma and CSF viral genome revealed only two non-coding changes compared with the original infecting virus. INTERPRETATION: Our report shows that previously unanticipated, late, severe relapses of Ebola virus can occur, in this case in the CNS. This finding fundamentally redefines what is known about the natural history of Ebola virus infection. Vigilance should be maintained in the thousands of Ebola survivors for cases of relapsed infection. The potential for these cases to initiate new transmission chains is a serious public health concern. FUNDING: Royal Free London NHS Foundation Trust.

Interleukin-17 Is Required for Control of Chronic Lung Infection Caused by Pseudomonas aeruginosa.

Chronic pulmonary infection with Pseudomonas aeruginosa is a feature of cystic fibrosis (CF) and other chronic lung diseases. Cytokines of the interleukin-17 (IL-17) family have been proposed as important in the host response to P. aeruginosa infection through their role in augmenting antibacterial immune responses, although their proinflammatory effect may contribute to lung damage that occurs as a result of chronic infection. We set out to explore the role of IL-17 in the host response to chronic P. aeruginosa infection. We used a murine model of chronic pulmonary infection with CF-related strains of P. aeruginosa We demonstrate that IL-17 cytokine signaling is essential for mouse survival and prevention of chronic infection at 2 weeks postinoculation using two different P. aeruginosa strains. Following infection, there was a marked expansion of cells within mediastinal lymph nodes, comprised mainly of innate lymphoid cells (ILCs); ∼90% of IL-17-producing (IL-17+) cells had markers consistent with group 3 ILCs. A smaller percentage of IL-17+ cells had markers consistent with a B1 phenotype. In lung homogenates harvested 14 days following infection, there was a significant expansion of IL-17+ cells; about 50% of these were CD3+, split equally between CD4+ Th17 cells and γδ T cells, while the CD3- IL-17+ cells were almost exclusively group 3 ILCs. Further experiments with B cell-deficient mice showed that B cell production of IL-17 or natural antibodies did not provide any defense against chronic P. aeruginosa infection. Thus, IL-17 rather than antibody is a key element in host defense against chronic pulmonary infection with P. aeruginosa.

Improving outcomes in acute and chronic periprosthetic hip and knee joint infection with a multidisciplinary approach.

AIMS: Periprosthetic hip and knee infection remains one of the most severe complications following arthroplasty, with an incidence between 0.5% to 1%. This study compares the outcomes of revision surgery for periprosthetic joint infection (PJI) following hip and knee arthroplasty prior to and after implementation of a specialist PJI multidisciplinary team (MDT). METHODS: Data was retrospectively analyzed from a single centre. In all, 29 consecutive joints prior to the implementation of an infection MDT in November 2016 were compared with 29 consecutive joints subsequent to the MDT conception. All individuals who underwent a debridement antibiotics and implant retention (DAIR) procedure, a one-stage revision, or a two-stage revision for an acute or chronic PJI in this time period were included. The definition of successfully treated PJI was based on the Delphi international multidisciplinary consensus. RESULTS: There were no statistically significant differences in patient demographics or comorbidities between the groups. There was also no significant difference in length of overall hospital stay (p = 0.530). The time taken for formal microbiology advice was significantly shorter in the post MDT group (p = 0.0001). There was a significant difference in failure rates between the two groups (p = 0.001), with 12 individuals (41.38%) pre-MDT requiring further revision surgery compared with one individual (6.67%) post-MDT inception. CONCLUSION: Our standardized multidisciplinary approach for periprosthetic knee and hip joint infection shows a significant reduction in failure rates following revision surgery. Following implementation of our MDT, our success rate in treating PJI is 96.55%, higher than what current literature suggests. We advocate the role of a specialist infection MDT in the management of patients with a PJI to allow an individualized patient-centred approach and care plan, thereby reducing postoperative complications and failure rates. Cite this article: Bone Jt Open 2021;2(7):509-514.

Dual RNA-seq in Streptococcus pneumoniae Infection Reveals Compartmentalized Neutrophil Responses in Lung and Pleural Space.

Streptococcus pneumoniae is the dominant cause of community-acquired pneumonia worldwide. Invasion of the pleural space is common and results in increased mortality. We set out to determine the bacterial and host factors that influence invasion of the pleural space. In a murine model of pneumococcal infection, we isolated neutrophil-dominated samples of bronchoalveolar and pleural fluid containing bacteria 48 hours after infection. Using dual RNA sequencing (RNA-seq), we characterized bacterial and host transcripts that were differentially regulated between these compartments and bacteria in broth and resting neutrophils, respectively. Pleural and lung samples showed upregulation of genes involved in the positive regulation of neutrophil extravasation but downregulation of genes mediating bacterial killing. Compared to the lung samples, cells within the pleural space showed marked upregulation of many genes induced by type I interferons, which are cytokines implicated in preventing bacterial transmigration across epithelial barriers. Differences in the bacterial transcripts between the infected samples and bacteria grown in broth showed the upregulation of genes in the bacteriocin locus, the pneumococcal surface adhesin PsaA, and the glycopeptide resistance gene vanZ; the gene encoding the ClpP protease was downregulated in infection. One hundred sixty-nine intergenic putative small bacterial RNAs were also identified, of which 43 (25.4%) small RNAs had been previously described. Forty-two of the small RNAs were upregulated in pleura compared to broth, including many previously identified as being important in virulence. Our results have identified key host and bacterial responses to invasion of the pleural space that can be potentially exploited to develop alternative antimicrobial strategies for the prevention and treatment of pneumococcal pleural disease.IMPORTANCE The factors that regulate the passage of bacteria between different anatomical compartments are unclear. We have used an experimental model of infection with Streptococcus pneumoniae to examine the host and bacterial factors involved in the passage of bacteria from the lung to the pleural space. The transcriptional profile of host and bacterial cells within the pleural space and lung was analyzed using deep sequencing of the entire transcriptome using the technique of dual RNA-seq. We found significant differences in the host and bacterial RNA profiles in infection, which shed light on the key factors that allow passage of this bacterium into the pleural space.

The interrelationship between phagocytosis, autophagy and formation of neutrophil extracellular traps following infection of human neutrophils by Streptococcus pneumoniae.

Neutrophils play an important role in the innate immune response to infection with Streptococcus pneumoniae, the pneumococcus. Pneumococci are phagocytosed by neutrophils and undergo killing after ingestion. Other cellular processes may also be induced, including autophagy and the formation of neutrophil extracellular traps (NETs), which may play a role in bacterial eradication. We set out to determine how these different processes interacted following pneumococcal infection of neutrophils, and the role of the major pneumococcal toxin pneumolysin in these various pathways. We found that pneumococci induced autophagy in neutrophils in a type III phosphatidylinositol-3 kinase dependent fashion that also required the autophagy gene Atg5. Pneumolysin did not affect this process. Phagocytosis was inhibited by pneumolysin but enhanced by autophagy, while killing was accelerated by pneumolysin but inhibited by autophagy. Pneumococci induced extensive NET formation in neutrophils that was not influenced by pneumolysin but was critically dependent on autophagy. While pneumolysin did not affect NET formation, it had a potent inhibitory effect on bacterial trapping within NETs. These findings show a complex interaction between phagocytosis, killing, autophagy and NET formation in neutrophils following pneumococcal infection that contribute to host defence against this pathogen.

IL-22 exacerbates weight loss in a murine model of chronic pulmonary Pseudomonas aeruginosa infection.

BACKGROUND: Interleukin (IL)-22 is a critical mediator of mucosal immunity and tissue regeneration, protecting against a number of respiratory pathogens. Whether IL-22 confers protection against chronic Pseudomonas aeruginosa (PA) infection in cystic fibrosis (CF) is unknown. METHODS: Explanted CF lungs were examined for IL-22 production and immune-localization. A murine model of persistent pulmonary PA infection was used to examine production of IL-22 following infective challenge. The role of IL-22 was examined using IL-22 knockout (KO) animals. RESULTS: IL-22 is produced within the adult CF lung and localizes to the airway epithelium. IL-22 is produced by murine pulmonary lymph node cells following lung infection. The absence of IL-22 resulted in no significant difference in acute mortality, bacterial burden, chronic infection rates, histological changes or neutrophilic inflammation in the chronic PA infection model. However, IL-22 KO animals lost less weight following infection. CONCLUSION: IL-22 is produced in the CF lung and in response to PA infection yet is dispensable in protection against chronic pulmonary P. aeruginosa infection in a murine model. However, we identified a novel role for the cytokine in promoting infection-related weight-loss, a significant prognostic factor in the CF population.

Efficacy of species-specific protein antibiotics in a murine model of acute Pseudomonas aeruginosa lung infection.

Protein antibiotics, known as bacteriocins, are widely produced by bacteria for intraspecies competition. The potency and targeted action of bacteriocins suggests that they could be developed into clinically useful antibiotics against highly drug resistant Gram-negative pathogens for which there are few therapeutic options. Here we show that Pseudomonas aeruginosa specific bacteriocins, known as pyocins, show strong efficacy in a murine model of P. aeruginosa lung infection, with the concentration of pyocin S5 required to afford protection from a lethal infection at least 100-fold lower than the most commonly used inhaled antibiotic tobramycin. Additionally, pyocins are stable in the lung, poorly immunogenic at high concentrations and efficacy is maintained in the presence of pyocin specific antibodies after repeated pyocin administration. Bacteriocin encoding genes are frequently found in microbial genomes and could therefore offer a ready supply of highly targeted and potent antibiotics active against problematic Gram-negative pathogens.

Mitochondrial damage contributes to Pseudomonas aeruginosa activation of the inflammasome and is downregulated by autophagy.

The nucleotide-binding domain, leucine-rich repeat containing family caspase recruitment domain containing 4 (NLRC4) inflammasome can be activated by pathogenic bacteria via products translocated through the microbial type III secretion apparatus (T3SS). Recent work has shown that activation of the NLRP3 inflammasome is downregulated by autophagy, but the influence of autophagy on NLRC4 activation is unclear. We set out to determine how autophagy might influence this process, using the bacterium Pseudomonas aeruginosa, which activates the NLRC4 inflammasome via its T3SS. Infection resulted in T3SS-dependent mitochondrial damage with increased production of reactive oxygen intermediates and release of mitochondrial DNA. Inhibiting mitochondrial reactive oxygen release or degrading intracellular mitochondrial DNA abrogated NLRC4 inflammasome activation. Moreover, macrophages lacking mitochondria failed to activate NLRC4 following infection. Removal of damaged mitochondria by autophagy significantly attenuated NLRC4 inflammasome activation. Mitochondrial DNA bound specifically to NLRC4 immunoprecipitates and transfection of mitochondrial DNA directly activated the NLRC4 inflammasome; oxidation of the DNA enhanced this effect. Manipulation of autophagy altered the degree of inflammasome activation and inflammation in an in vivo model of P. aeruginosa infection. Our results reveal a novel mechanism contributing to NLRC4 activation by P. aeruginosa via mitochondrial damage and release of mitochondrial DNA triggered by the bacterial T3SS that is downregulated by autophagy.

Caspase-1 cleavage of the TLR adaptor TRIF inhibits autophagy and ß-interferon production during Pseudomonas aeruginosa infection.

Bacterial infection can trigger autophagy and inflammasome activation, but the effects of inflammasome activation on autophagy are unknown. We examined this in the context of Pseudomonas aeruginosa macrophage infection, which triggers NLRC4 inflammasome activation. P. aeruginosa induced autophagy via TLR4 and its adaptor TRIF. NLRC4 and caspase-1 activation following infection attenuated autophagy. Caspase-1 directly cleaved TRIF to diminish TRIF-mediated signaling, resulting in inhibition of autophagy and in reduced type I interferon production. Expression of a caspase-1 resistant TRIF mutant enhanced autophagy and type I interferon production following infection. Preventing TRIF cleavage by caspase-1 in an in vivo model of P. aeruginosa infection resulted in enhanced bacterial autophagy, attenuated IL-1ß production, and increased bacterial clearance. Additionally, TRIF cleavage by caspase-1 diminished NLRP3 inflammasome activation. Thus, caspase-1 mediated TRIF cleavage is a key event in controlling autophagy, type I interferon production, and inflammasome activation with important functional consequences.

What is different about serotype 1 pneumococci?

Serotype 1 Streptococcus pneumoniae is among the most commonly isolated serotype in invasive pneumococcal disease but is rarely found causing asymptomatic nasopharyngeal colonization. Compared to infection by other serotypes, infection caused by serotype 1 is more likely to be identified in young patients without comorbidities but is generally associated with a lower mortality. Empyema and extrapulmonary manifestations are common. Outbreaks of serotype 1 disease have been reported in closed communities and epidemics are particularly common in sub-Saharan Africa. The serotype 1 capsular polysaccharide is a zwitterionic structure that enables it to function as a T-cell dependent antigen under some circumstances, in contrast to other pneumococcal capsular polysaccharides that are T-cell independent antigens. There are also differences in the key virulence factor pneumolysin in some serotype 1 isolates. The clinical significance of these differences remains to be determined.

Acetazolamide for the prevention of acute mountain sickness--a systematic review and meta-analysis.

BACKGROUND: Acetazolamide has been reported to be effective in the prevention of acute mountain sickness (AMS). Our aim was to conduct a systematic review of randomized, placebo-controlled trials of acetazolamide in the prevention of AMS. METHODS: Studies were identified by searching the MEDLINE, Embase, Cochrane Clinical Trials Register, and ClinicalTrials.gov databases. Primary end point was difference in incidence of AMS between acetazolamide and placebo groups. RESULTS: Acetazolamide prophylaxis was associated with a 48% relative-risk reduction compared to placebo. There was no evidence of an association between efficacy and dose of acetazolamide. Adverse effects were often not systematically reported but appeared to be common but generally mild. One study found that adverse effects of acetazolamide were dose related. CONCLUSIONS: Acetazolamide is effective prophylaxis for the prevention of symptoms of AMS in those going to high altitude. A dose of 250 mg/day has similar efficacy to higher doses and may have a favorable side-effect profile.