The platelet activating factor receptor is not required for exacerbation of bacterial pneumonia following influenza

Respiratory tract barrier dysfunction in viral-bacterial co-infection cases

A preceding viral infection of the respiratory tract predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality. However, the underlying mechanism of the viral-bacterial synergy that leads to disease progression has remained elusive, thus hampering the production of effective prophylactic and therapeutic intervention options. In addition to viral-induced airway epithelial damage, which allows dissemination of bacteria to the lower respiratory tract and increases their invasiveness, dysfunction of immune defense following a viral infection has been implicated as a factor for enhanced susceptibility to secondary bacterial infections. Given the proximity of the oral cavity to the respiratory tract, where viruses enter and replicate, it is also well-established that oral health status can significantly influence the initiation, progression, and pathology of respiratory viral infections. This review was conducted to focus on the dysfunction of the respiratory barrier, which plays a crucial role in providing physical and secretory barriers as well as immune defense in the context of viral-bacterial synergy. Greater understanding of barrier response to viral-bacterial co-infections, will ultimately lead to development of effective, broad-spectrum therapeutic approaches for prevention of enhanced susceptibility to these pathogens.

Lung and Heart Biology of the Dp16 Mouse Model of down Syndrome: Implications for Studying Cardiopulmonary Disease

(1) Background: We sought to investigate the baseline lung and heart biology of the Dp16 mouse model of Down syndrome (DS) as a prelude to the investigation of recurrent respiratory tract infection. (2) Methods: In controls vs. Dp16 mice, we compared peripheral blood cell and plasma analytes. We examined baseline gene expression in lungs and hearts for key parameters related to susceptibility of lung infection. We investigated lung and heart protein expression and performed lung morphometry. Finally, and for the first time each in a model of DS, we performed pulmonary function testing and a hemodynamic assessment of cardiac function. (3) Results: Dp16 mice circulate unique blood plasma cytokines and chemokines. Dp16 mouse lungs over-express the mRNA of triplicated genes, but not necessarily corresponding proteins. We found a sex-specific decrease in the protein expression of interferon α receptors, yet an increased signal transducer and activator of transcription (STAT)-3 and phospho-STAT3. Platelet-activating factor receptor protein was not elevated in Dp16 mice. The lungs of Dp16 mice showed increased stiffness and mean linear intercept and contained bronchus-associated lymphoid tissue. The heart ventricles of Dp16 mice displayed hypotonicity. Finally, Dp16 mice required more ketamine to achieve an anesthetized state. (4) Conclusions: The Dp16 mouse model of DS displays key aspects of lung heart biology akin to people with DS. As such, it has the potential to be an extremely valuable model of recurrent severe respiratory tract infection in DS.

Effect of Influenza Vaccine on Prevention of Acute Attack of Chronic Airway Disease in Elderly Population

This study investigated the effect of influenza vaccination on prevention of acute attacks in elderly patients with chronic airway disease and provides evidence for the prevention and control strategy of chronic airway disease in the elderly population. A total of 348 elderly patients in Linquan County, Anhui Province, China, who were also in stationary phases of chronic airway disease and were vaccinated with either the tetravalent or trivalent influenza vaccine were selected. The number of patients with acute attacks, the number of outpatients with acute attacks, the number of outpatients, the number of inpatients, the total cost of patients, the cost of outpatients, the cost of hospitalization, and the length of hospitalization were collected before vaccination and after a one-year follow-up. There was no significant difference in age and sex ratio among the two vaccination groups. The ratios of acute attacks, outpatient visits, and hospitalizations and number of outpatient visits, number of hospitalizations, total medical expenses, outpatient expenses, and hospitalization expenses were significantly higher before vaccination than those after vaccination in both the trivalent-vaccination group and tetravalent-vaccination group. Additionally, there was no significant difference in the length of stay between before and after vaccination in either the trivalent-vaccination group or tetravalent-vaccination group. The protection effect between the trivalent-vaccination group and tetravalent-vaccination group was not significant. Influenza vaccination can effectively prevent the acute attack of chronic airway disease and delay the progress of chronic airway disease.

Secondary streptococcal infection following influenza

Secondary bacterial infection following influenza A virus (IAV) infection is a major cause of morbidity and mortality during influenza epidemics. Streptococcus pneumoniae has been identified as a predominant pathogen in secondary pneumonia cases that develop following influenza. Although IAV has been shown to enhance susceptibility to the secondary bacterial infection, the underlying mechanism of the viral-bacterial synergy leading to disease progression is complex and remains elusive. In this review, cooperative interactions of viruses and streptococci during co- or secondary infection with IAV are described. IAV infects the upper respiratory tract, therefore, streptococci that inhabit or infect the respiratory tract are of special interest. Since many excellent reviews on the co-infection of IAV and S. pneumoniae have already been published, this review is intended to describe the unique interactions between other streptococci and IAV. Both streptococcal and IAV infections modulate the host epithelial barrier of the respiratory tract in various ways. IAV infection directly disrupts epithelial barriers, though at the same time the virus modifies the properties of infected cells to enhance streptococcal adherence and invasion. Mitis group streptococci produce neuraminidases, which promote IAV infection in a unique manner. The studies reviewed here have revealed intriguing mechanisms underlying secondary streptococcal infection following influenza. This article is protected by copyright. All rights reserved.

The Effectiveness of Influenza Vaccination on Chronic Obstructive Pulmonary Disease with Different Severities of Airflow Obstruction

This retrospective study included COPD patients who attended our medical center between January and October 2018, and analyzed the outcomes of their influenza vaccination, including medical visits, hospitalization, medical expenses, and the incidence of respiratory failure. Airflow limitation was stratified according to GOLD guidelines. Overall, 543 COPD patients were enrolled, including 197, 113, 126, and 107 mild, moderate, severe, and very severe patients, respectively. Of all the participants, 238 received an influenza vaccination (43.8%), which significantly reduced hospital utilization for moderate (odds ratio [OR] 0.22, 95%CI 0.09–0.51), severe (OR 0.19, 95%CI 0.08–0.44), and very severe patients (OR 0.15, 95%CI 0.05–0.5) compared to mild patients (OR 0.51, 95%CI 0.2–1.26); reduced emergency department utilization for moderate (OR 0.33, 95%CI 0.14–0.77), severe (OR 0.22, 95%CI 0.10–0.52), and very severe patients (OR 0.30, 95%CI 0.10–0.88) compared to mild patients (OR 0.64, 95%CI 0.30–1.37); and reduced the occurrence of respiratory failure for moderate (OR 0.20, 95%CI 0.06–0.68), severe (OR 0.40, 95%CI 0.16–0.98), and very severe patients (OR 0.36, 95%CI 0.15–0.82) compared to mild patients (OR 0% CI 0.14–3.20). Influenza vaccination is more effective in COPD patients with moderate, severe, and very severe airflow obstruction than in those with mild obstruction with respect to hospital utilization, emergency department utilization, and respiratory failure.

GP96 Drives Exacerbation of Secondary Bacterial Pneumonia following Influenza A Virus Infection

Influenza A virus (IAV) infection predisposes the host to secondary bacterial pneumonia, known as a major cause of morbidity and mortality during influenza virus epidemics. Analysis of interactions between IAV-infected human epithelial cells and Streptococcus pneumoniae revealed that infected cells ectopically exhibited the endoplasmic reticulum chaperone glycoprotein 96 (GP96) on the surface. Importantly, efficient pneumococcal adherence to epithelial cells was imparted by interactions with extracellular GP96 and integrin α_V, with the surface expression mediated by GP96 chaperone activity. Furthermore, abrogation of adherence was gained by chemical inhibition or genetic knockout of GP96 as well as addition of RGD peptide, an inhibitor of integrin-ligand interactions. Direct binding of extracellular GP96 and pneumococci was shown to be mediated by pneumococcal oligopeptide permease components. Additionally, IAV infection induced activation of calpains and Snail1, which are responsible for degradation and transcriptional repression of junctional proteins in the host, respectively, indicating increased bacterial translocation across the epithelial barrier. Notably, treatment of IAV-infected mice with the GP96 inhibitor enhanced pneumococcal clearance from lung tissues and ameliorated lung pathology. Taken together, the present findings indicate a viral-bacterial synergy in relation to disease progression and suggest a paradigm for developing novel therapeutic strategies tailored to inhibit pneumococcal colonization in an IAV-infected respiratory tract.

Molecular pathogenesis of secondary bacterial infection associated to viral infections including SARS-CoV-2

Secondary bacterial infections are commonly associated with prior or concomitant respiratory viral infections. Viral infections damage respiratory airways and simultaneously defects both innate and acquired immune response that provides a favorable environment for bacterial growth, adherence, and facilitates invasion into healthy sites of the respiratory tract. Understanding the molecular mechanism of viral-induced secondary bacterial infections will provide us a chance to develop novel and effective therapeutic approaches for disease prevention. The present study describes details about the secondary bacterial infection during viral infections and their immunological changes.The outcome of discussion avails an opportunity to understand possible secondary bacterial infections associated with novel SARS-CoV-2, presently causing pandemic outbreak COVID-19.

Why Are Children With Bronchiolitis At Risk Of Urinary Tract Infections?

Viral respiratory infections are frequently eliminated from human bodies without any sequelae. Secondary serious bacterial infection (SBI) in children with acute bronchiolitis has been an apprehension expressed by health care providers. Several published studies have shown an association between acute bronchiolitis and secondary bacterial infection, including urinary tract infections (UTI). However, the proposed mechanism by which a virus can induce UTIs is not yet known. The aim of this commentary is to update the current evidence of risk of UTI in children with bronchiolitis. We present several clinical studies related to the topic as well as a brief review of the potential pathophysiology of secondary infections that could present with viral respiratory illness.

Mathematical modeling of postcoinfection with influenza A virus and Streptococcus pneumoniae, with implications for pneumonia and COPD-risk assessment

Background

The interaction between influenza and pneumococcus is important for understanding how coinfection may exacerbate pneumonia. Secondary pneumococcal pneumonia associated with influenza infection is more likely to increase respiratory morbidity and mortality. This study aimed to assess exacerbated inflammatory effects posed by secondary pneumococcal pneumonia, given prior influenza infection.

Materials and methods

A well-derived mathematical within-host dynamic model of coinfection with influenza A virus and Streptococcus pneumoniae (SP) integrated with dose–response relationships composed of previously published mouse experimental data and clinical studies was implemented to study potentially exacerbated inflammatory responses in pneumonia based on a probabilistic approach.

Results

We found that TNFα is likely to be the most sensitive biomarker reflecting inflammatory response during coinfection among three explored cytokines. We showed that the worst inflammatory effects would occur at day 7 SP coinfection, with risk probability of 50% (likely) to develop severe inflammatory responses. Our model also showed that the day of secondary SP infection had much more impact on the severity of inflammatory responses in pneumonia compared to the effects caused by initial virus titers and bacteria loads.

Conclusion

People and health care workers should be wary of secondary SP infection on day 7 post-influenza infection for prompt and proper control-measure implementation. Our quantitative risk-assessment framework can provide new insights into improvements in respiratory health especially, predominantly due to chronic obstructive pulmonary disease (COPD).

Secondary Bacterial Infections Associated with Influenza Pandemics

Lower and upper respiratory infections are the fourth highest cause of global mortality (Lozano et al., 2012). Epidemic and pandemic outbreaks of respiratory infection are a major medical concern, often causing considerable disease and a high death toll, typically over a relatively short period of time. Influenza is a major cause of epidemic and pandemic infection. Bacterial co/secondary infection further increases morbidity and mortality of influenza infection, with Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus reported as the most common causes. With increased antibiotic resistance and vaccine evasion it is important to monitor the epidemiology of pathogens in circulation to inform clinical treatment and development, particularly in the setting of an influenza epidemic/pandemic.

Viral-bacterial interactions in the respiratory tract

In the respiratory tract, viruses and bacteria can interact on multiple levels. It is well known that respiratory viruses, particularly influenza viruses, increase the susceptibility to secondary bacterial infections. Numerous mechanisms, including compromised physical and immunological barriers, and changes in the microenvironment have hereby been shown to contribute to the development of secondary bacterial infections. In contrast, our understanding of how bacteria shape a response to subsequent viral infection is still limited. There is emerging evidence that persistent infection (or colonization) of the lower respiratory tract (LRT) with potential pathogenic bacteria, as observed in diseases like chronic obstructive pulmonary disease or cystic fibrosis, modulates subsequent viral infections by increasing viral entry receptors and modulating the inflammatory response. Moreover, recent studies suggest that even healthy lungs are not, as had long been assumed, sterile. The composition of the lung microbiome may thus modulate responses to viral infections. Here we summarize the current knowledge on the co-pathogenesis between viruses and bacteria in LRT infections.

Virus-induced secondary bacterial infection: a concise review

Respiratory diseases are a very common source of morbidity and mortality among children. Health care providers often face a dilemma when encountering a febrile infant or child with respiratory tract infection. The reason expressed by many clinicians is the trouble to confirm whether the fever is caused by a virus or a bacterium. The aim of this review is to update the current evidence on the virus-induced bacterial infection. We present several clinical as well in vitro studies that support the correlation between virus and secondary bacterial infections. In addition, we discuss the pathophysiology and prevention modes of the virus–bacterium coexistence. A search of the PubMed and MEDLINE databases was carried out for published articles covering bacterial infections associated with respiratory viruses. This review should provide clinicians with a comprehensive idea of the range of bacterial and viral coinfections or secondary infections that could present with viral respiratory illness.

Type I interferon protects against pneumococcal invasive disease by inhibiting bacterial transmigration across the lung

Streptococcus pneumoniae infection is a leading cause of bacterial pneumonia, sepsis and meningitis and is associated with high morbidity and mortality. Type I interferon (IFN-I), whose contribution to antiviral and intracellular bacterial immunity is well established, is also elicited during pneumococcal infection, yet its functional significance is not well defined. Here, we show that IFN-I plays an important role in the host defense against pneumococci by counteracting the transmigration of bacteria from the lung to the blood. Mice that lack the type I interferon receptor (Ifnar1^−/−) or mice that were treated with a neutralizing antibody against the type I interferon receptor, exhibited enhanced development of bacteremia following intranasal pneumococcal infection, while maintaining comparable bacterial numbers in the lung. In turn, treatment of mice with IFNβ or IFN-I-inducing synthetic double stranded RNA (poly(I:C)), dramatically reduced the development of bacteremia following intranasal infection with S. pneumoniae. IFNβ treatment led to upregulation of tight junction proteins and downregulation of the pneumococcal uptake receptor, platelet activating factor receptor (PAF receptor). In accordance with these findings, IFN-I reduced pneumococcal cell invasion and transmigration across epithelial and endothelial layers, and Ifnar1^−/− mice showed overall enhanced lung permeability. As such, our data identify IFN-I as an important component of the host immune defense that regulates two possible mechanisms involved in pneumococcal invasion, i.e. PAF receptor-mediated transcytosis and tight junction-dependent pericellular migration, ultimately limiting progression from a site-restricted lung infection to invasive, lethal disease.

Streptococcus pneumoniae infection is a leading cause of bacterial pneumonia and invasive diseases such as sepsis and meningitis, which are associated with high morbidity and mortality. Here we identified type I Interferons (IFN-I) as critical mediators that prevent the progression of a local lung infection with S. pneumoniae to invasive disease. We found that mice lacking the receptor for IFN-I, or which received antibodies that interfere with receptor activation, showed increased development of bacteremia upon lung infection with S. pneumoniae. Treating mice, or cell lines, with IFN-I protected against bacterial migration across epithelial and endothelial cell barriers, correlating with increased expression of tight junction proteins, which enhance the lung's barrier function, and reduced surface expression levels of platelet activating factor receptor, a host receptor known to be hijacked by bacteria for migration across the lung/blood and blood/brain barriers. Together, our results identify IFN-I as an important component of the host immune defense against invasion from a gram-positive, extracellular bacterium, possibly reflecting a general mechanism for the regulation of epithelial and endothelial barrier function that is critical for protection from pathogen invasion.

Immune dysfunction and bacterial coinfections following influenza

Secondary pulmonary infections by encapsulated bacteria including Streptococcus pneumoniae and Staphylococcus aureus following influenza represent a common and challenging clinical problem. The reasons for this polymicrobial synergy are still not completely understood, hampering development of effective prophylactic and therapeutic interventions. Although it has been commonly thought that viral-induced epithelial cell damage allows bacterial invasiveness, recent studies by several groups have now implicated dysfunctional innate immune defenses following influenza as the primary culprit for enhanced susceptibility to secondary bacterial infections. Understanding the immunological imbalances that are responsible for virus/bacteria synergy will ultimately allow the design of effective, broad-spectrum therapeutic approaches for prevention of enhanced susceptibility to these pathogens.

Time and dose-dependent risk of pneumococcal pneumonia following influenza: a model for within-host interaction between influenza and Streptococcus pneumoniae

A significant fraction of seasonal and in particular pandemic influenza deaths are attributed to secondary bacterial infections. In animal models, influenza virus predisposes hosts to severe infection with both Streptococcus pneumoniae and Staphylococcus aureus. Despite its importance, the mechanistic nature of the interaction between influenza and pneumococci, its dependence on the timing and sequence of infections as well as the clinical and epidemiological consequences remain unclear. We explore an immune-mediated model of the viral-bacterial interaction that quantifies the timing and the intensity of the interaction. Taking advantage of the wealth of knowledge gained from animal models, and the quantitative understanding of the kinetics of pathogen-specific immunological dynamics, we formulate a mathematical model for immune-mediated interaction between influenza virus and S. pneumoniae in the lungs. We use the model to examine the pathogenic effect of inoculum size and timing of pneumococcal invasion relative to influenza infection, as well as the efficacy of antivirals in preventing severe pneumococcal disease. We find that our model is able to capture the key features of the interaction observed in animal experiments. The model predicts that introduction of pneumococcal bacteria during a 4-6 day window following influenza infection results in invasive pneumonia at significantly lower inoculum size than in hosts not infected with influenza. Furthermore, we find that antiviral treatment administered later than 4 days after influenza infection was not able to prevent invasive pneumococcal disease. This work provides a quantitative framework to study interactions between influenza and pneumococci and has the potential to accurately quantify the interactions. Such quantitative understanding can form a basis for effective clinical care, public health policies and pandemic preparedness.

Signalling or binding: the role of the platelet-activating factor receptor in invasive pneumococcal disease

Streptococcus pneumoniae (the pneumococcus) is an opportunistic human pathogen, which causes serious invasive disease such as pneumonia, bacteraemia and meningitis. The interaction of the bacteria with host receptors precedes the development of invasive disease. One host receptor implicated in pneumococcal adhesion to, invasion of and ultimately translocation of cell layers is the platelet-activating factor receptor (PAFR). PAFR is a G-protein coupled receptor which binds PAF, a potent phospholipid activator involved in many leucocyte functions, platelet aggregation and inflammation. PAFR has been proposed to bind S. pneumoniae and as such facilitate adhesion to, uptake by and transcytosis of endothelial cells leading to invasive disease. However, there is a shortage of biochemical data supporting direct interaction between PAFR and the bacteria, in addition to conflicting data on its role in development of invasive pneumococcal disease (IPD). In this review, we will discuss current literature on PAFR and S. pneumoniae and other pathogens,including data concerning human PAFR genetic variation related to IPD clinical aspects, to shed light on the importance of PAFR in IPD. Clarification of the role of this receptor in IPD development has the potential to enable the development of novel therapeutic strategies for treating pneumococcal disease by interfering with the PAFR.

Clarithromycin suppresses human respiratory syncytial virus infection-induced Streptococcus pneumoniae adhesion and cytokine production in a pulmonary epithelial cell line

Human respiratory syncytial virus (RSV) sometimes causes acute and severe lower respiratory tract illness in infants and young children. RSV strongly upregulates proinflammatory cytokines and the platelet-activating factor (PAF) receptor, which is a receptor for Streptococcus pneumoniae, in the pulmonary epithelial cell line A549. Clarithromycin (CAM), which is an antimicrobial agent and is also known as an immunomodulator, significantly suppressed RSV-induced production of interleukin-6, interleukin-8, and regulated on activation, normal T-cell expressed and secreted (RANTES). CAM also suppressed RSV-induced PAF receptor expression and adhesion of fluorescein-labeled S. pneumoniae cells to A549 cells. The RSV-induced S. pneumoniae adhesion was thought to be mediated by the host cell's PAF receptor. CAM, which exhibits antimicrobial and immunomodulatory activities, was found in this study to suppress the RSV-induced adhesion of respiratory disease-causing bacteria, S. pneumoniae, to host cells. Thus, CAM might suppress immunological disorders and prevent secondary bacterial infections during RSV infection.

Infection with human coronavirus NL63 enhances streptococcal adherence to epithelial cells

Understanding the mechanisms of augmented bacterial pathogenicity in post-viral infections is the first step in the development of an effective therapy. This study assessed the effect of human coronavirus NL63 (HCoV-NL63) on the adherence of bacterial pathogens associated with respiratory tract illnesses. It was shown that HCoV-NL63 infection resulted in an increased adherence of Streptococcus pneumoniae to virus-infected cell lines and fully differentiated primary human airway epithelium cultures. The enhanced binding of bacteria correlated with an increased expression level of the platelet-activating factor receptor (PAF-R), but detailed evaluation of the bacterium-PAF-R interaction revealed a limited relevance of this process.

The airway epithelium: soldier in the fight against respiratory viruses

The airway epithelium acts as a frontline defense against respiratory viruses, not only as a physical barrier and through the mucociliary apparatus but also through its immunological functions. It initiates multiple innate and adaptive immune mechanisms which are crucial for efficient antiviral responses. The interaction between respiratory viruses and airway epithelial cells results in production of antiviral substances, including type I and III interferons, lactoferrin, β-defensins, and nitric oxide, and also in production of cytokines and chemokines, which recruit inflammatory cells and influence adaptive immunity. These defense mechanisms usually result in rapid virus clearance. However, respiratory viruses elaborate strategies to evade antiviral mechanisms and immune responses. They may disrupt epithelial integrity through cytotoxic effects, increasing paracellular permeability and damaging epithelial repair mechanisms. In addition, they can interfere with immune responses by blocking interferon pathways and by subverting protective inflammatory responses toward detrimental ones. Finally, by inducing overt mucus secretion and mucostasis and by paving the way for bacterial infections, they favor lung damage and further impair host antiviral mechanisms.

Preventing and treating secondary bacterial infections with antiviral agents

Bacterial super-infections contribute to the significant morbidity and mortality associated with influenza and other respiratory virus infections. There are robust animal model data, but only limited clinical information on the effectiveness of licensed antiviral agents for the treatment of bacterial complications of influenza. The association of secondary bacterial pathogens with fatal pneumonia during the recent H1N1 influenza pandemic highlights the need for new development in this area. Basic and clinical research into viral-bacterial interactions over the past decade has revealed several mechanisms that underlie this synergism. By applying these insights to antiviral drug development, the potential exists to improve outcomes by means other than direct inhibition of the virus.

Platelet-activating factor receptor plays a role in lung injury and death caused by Influenza A in mice

Influenza A virus causes annual epidemics which affect millions of people worldwide. A recent Influenza pandemic brought new awareness over the health impact of the disease. It is thought that a severe inflammatory response against the virus contributes to disease severity and death. Therefore, modulating the effects of inflammatory mediators may represent a new therapy against Influenza infection. Platelet activating factor (PAF) receptor (PAFR) deficient mice were used to evaluate the role of the gene in a model of experimental infection with Influenza A/WSN/33 H1N1 or a reassortant Influenza A H3N1 subtype. The following parameters were evaluated: lethality, cell recruitment to the airways, lung pathology, viral titers and cytokine levels in lungs. The PAFR antagonist PCA4248 was also used after the onset of flu symptoms. Absence or antagonism of PAFR caused significant protection against flu-associated lethality and lung injury. Protection was correlated with decreased neutrophil recruitment, lung edema, vascular permeability and injury. There was no increase of viral load and greater recruitment of NK1.1⁺ cells. Antibody responses were similar in WT and PAFR-deficient mice and animals were protected from re-infection. Influenza infection induces the enzyme that synthesizes PAF, lyso-PAF acetyltransferase, an effect linked to activation of TLR7/8. Therefore, it is suggested that PAFR is a disease-associated gene and plays an important role in driving neutrophil influx and lung damage after infection of mice with two subtypes of Influenza A. Further studies should investigate whether targeting PAFR may be useful to reduce lung pathology associated with Influenza A virus infection in humans.

Influenza virus causes disease that affects people from different age, gender or social conditions. The illness spreads easily and affects millions of people every year. Vaccines are effective preventive approaches, but the high degree of viral antigenic drift requires annual formulation. Anti-viral drugs are used as therapy, but are only effective at the very early stages of disease. The main symptoms that lead to hospitalizations and deaths are associated with the severe inflammatory host immune response triggered by the virus infection. Our approach was to decrease the inflammatory events associated with the viral infection by targeting a molecule, Platelet Activating Factor receptor (PAFR), known to induce several inflammatory events, including leukocyte recruitment and leakage. We found that PAFR deficient mice or wild type mice treated with a PAFR antagonist had less pulmonary inflammation, pulmonary injury and lethality rates when infected by two subtypes of Influenza A virus. In contrast, the immune response against the virus, as assessed by viral loads and specific antibodies, were not decreased. Our findings concur with the idea that severe inflammation plays an important role in flu morbidity and mortality and show that PAFR is a major driver of the exacerbated inflammation in mice infected with Influenza A virus.

Interaction between influenza virus and Streptococcus pneumoniae in severe pneumonia

The contribution of bacterial superinfection to influenza-associated pneumonia morbidity and mortality is evident from the 1918 and 1957 influenza pandemics, and is supported by a number of murine model studies. Murine model studies have also assisted in helping to expand our understanding of the pathogenesis of the interaction between the influenza virus and subsequent susceptibility to pneumococcal superinfections. The purported impact that the pneumococcal conjugate vaccine has had on reducing the burden of confirmed influenza-associated pneumonia, as well as upon all-cause clinical pneumonia, provides additional clinical evidence of the role of superimposed pneumococcal infections as a cause of severe pneumonia in children. Using this information together with the evidence for the effectiveness of influenza vaccination against influenza-associated pneumonia, it is imperative that preventive strategies for future influenza pandemic preparedness include broad-based vaccination against pneumococci, as well as ensuring that adequate antimicrobials are available for the early treatment of influenza virus, in addition to pneumococcal and other bacterial infections.

Bench-to-bedside review: bacterial pneumonia with influenza - pathogenesis and clinical implications

Seasonal and pandemic influenza are frequently complicated by bacterial infections, causing additional hospitalization and mortality. Secondary bacterial respiratory infection can be subdivided into combined viral/bacterial pneumonia and post-influenza pneumonia, which differ in their pathogenesis. During combined viral/bacterial infection, the virus, the bacterium and the host interact with each other. Post-influenza pneumonia may, at least in part, be due to resolution of inflammation caused by the primary viral infection. These mechanisms restore tissue homeostasis but greatly impair the host response against unrelated bacterial pathogens. In this review we summarize the underlying mechanisms leading to combined viral/bacterial infection or post-influenza pneumonia and highlight important considerations for effective treatment of bacterial pneumonia during and shortly after influenza.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.