Cellular effectors mediating Th17-dependent clearance of pneumococcal colonization in mice

Synthetic BSA-conjugated disaccharide related to the Streptococcus pneumoniae serotype 3 capsular polysaccharide increases IL-17A Levels, γδ T cells, and B1 cells in mice

The disaccharide (β-D-glucopyranosyluronic acid)-(1→4)-β-D-glucopyranoside represents a repeating unit of the capsular polysaccharide of Streptococcus pneumoniae serotype 3. A conjugate of the disaccharide with BSA (di-BSA conjugate) adjuvanted with aluminum hydroxide induced - in contrast to the non-adjuvanted conjugate - IgG1 antibody production and protected mice against S. pneumoniae serotype 3 infection after intraperitoneal prime-boost immunization. Adjuvanted and non-adjuvanted conjugates induced production of Th1 (IFNγ, TNFα); Th2 (IL-5, IL-13); Th17 (IL-17A), Th1/Th17 (IL-22), and Th2/Th17 cytokines (IL-21) after immunization. The concentration of cytokines in mice sera was higher in response to the adjuvanted conjugate, with the highest level of IL-17A production after the prime and boost immunizations. In contrast, the non-adjuvanted conjugate elicited only weak production of IL-17A, which gradually decreased after the second immunization. After boost immunization of mice with the adjuvanted di-BSA conjugate, there was a significant increase in the number of CD45+/CD19+ B cells, TCR+ γδ T cell, CD5+ В1 cells, and activated cells with MHC II+ expression in the spleens of the mice. IL-17A, TCR+ γδ T cells, and CD5+ В1 cells play a crucial role in preventing pneumococcal infection, but can also contribute to autoimmune diseases. Immunization with the adjuvanted and non-adjuvanted di-BSA conjugate did not elicit autoantibodies against double-stranded DNA targeting cell nuclei in mice. Thus, the molecular and cellular markers associated with antibody production and protective activity in response to immunization with the di-BSA conjugate adjuvanted with aluminum hydroxide are IL-17A, TCR+ γδ T cells, and CD5+ В1 cells against the background of increasing MHC II+ expression.

Impaired upper respiratory tract barrier function during postnatal development predisposes to invasive pneumococcal disease

Infants are highly susceptible to invasive respiratory and gastrointestinal infections. To elucidate the age-dependent mechanism(s) that drive bacterial spread from the mucosa, we developed an infant mouse model using the prevalent pediatric respiratory pathogen, Streptococcus pneumoniae (Spn). Despite similar upper respiratory tract (URT) colonization levels, the survival rate of Spn-infected infant mice was significantly decreased compared to adults and corresponded with Spn dissemination to the bloodstream. An increased rate of pneumococcal bacteremia in early life beyond the newborn period was attributed to increased bacterial translocation across the URT barrier. Bacterial dissemination in infant mice was independent of URT monocyte or neutrophil infiltration, phagocyte-derived ROS or RNS, inflammation mediated by toll-like receptor 2 or interleukin 1 receptor signaling, or the pore-forming toxin pneumolysin. Using molecular barcoding of Spn, we found that only a minority of bacterial clones in the nasopharynx disseminated to the blood in infant mice, indicating the absence of robust URT barrier breakdown. Rather, transcriptional profiling of the URT epithelium revealed a failure of infant mice to upregulate genes involved in the tight junction pathway. Expression of many such genes was also decreased in early life in humans. Infant mice also showed increased URT barrier permeability and delayed mucociliary clearance during the first two weeks of life, which corresponded with tighter attachment of bacteria to the respiratory epithelium. Together, these results demonstrate a window of vulnerability during postnatal development when altered mucosal barrier function facilitates bacterial dissemination.

Lipidation of pneumococcal proteins enables activation of human antigen-presenting cells and initiation of an adaptive immune response

Streptococcus pneumoniae remains a significant global threat, with existing vaccines having important limitations such as restricted serotype coverage and high manufacturing costs. Pneumococcal lipoproteins are emerging as promising vaccine candidates due to their surface exposure and conservation across various serotypes. While prior studies have explored their potential in mice, data in a human context and insights into the impact of the lipid moiety remain limited. In the present study, we examined the immunogenicity of two pneumococcal lipoproteins, DacB and MetQ, both in lipidated and non-lipidated versions, by stimulation of primary human immune cells. Immune responses were assessed by the expression of common surface markers for activation and maturation as well as cytokines released into the supernatant. Our findings indicate that in the case of MetQ lipidation was crucial for activation of human antigen-presenting cells such as dendritic cells and macrophages, while non-lipidated DacB demonstrated an intrinsic potential to induce an innate immune response. Nevertheless, immune responses to both proteins were enhanced by lipidation. Interestingly, following stimulation of dendritic cells with DacB, LipDacB and LipMetQ, cytokine levels of IL-6 and IL-23 were significantly increased, which are implicated in triggering potentially important Th17 cell responses. Furthermore, LipDacB and LipMetQ were able to induce proliferation of CD4+ T cells indicating their potential to induce an adaptive immune response. These findings contribute valuable insights into the immunogenic properties of pneumococcal lipoproteins, emphasizing their potential role in vaccine development against pneumococcal infections.

Genomic and panproteomic analysis of the development of infant immune responses to antigenically-diverse pneumococci

Streptococcus pneumoniae (pneumococcus) is a nasopharyngeal commensal and respiratory pathogen. This study characterises the immunoglobulin G (IgG) repertoire recognising pneumococci from birth to 24 months old (mo) in a prospectively-sampled cohort of 63 children using a panproteome array. IgG levels are highest at birth, due to transplacental transmission of maternal antibodies. The subsequent emergence of responses to individual antigens exhibit distinct kinetics across the cohort. Stable differences in the strength of individuals' responses, correlating with maternal IgG concentrations, are established by 6 mo. By 12 mo, children develop unique antibody profiles that are boosted by re-exposure. However, some proteins only stimulate substantial responses in adults. Integrating genomic data on nasopharyngeal colonisation demonstrates rare pneumococcal antigens can elicit strong IgG levels post-exposure. Quantifying such responses to the diverse core loci (DCL) proteins is complicated by cross-immunity between variants. In particular, the conserved N terminus of DCL protein zinc metalloprotease B provokes the strongest early IgG responses. DCL proteins' ability to inhibit mucosal immunity likely explains continued pneumococcal carriage despite hosts' polyvalent antibody repertoire. Yet higher IgG levels are associated with reduced incidence, and severity, of pneumonia, demonstrating the importance of the heterogeneity in response strength and kinetics across antigens and individuals.

IL-27 mediates immune response of pneumococcal vaccine SPY1 through Th17 and memory CD4+T cells

Vaccination is an effective means of preventing pneumococcal disease and SPY1 is a live attenuated pneumococcal vaccine we obtained earlier. We found IL-27 and its specific receptor (WSX-1) were increased in SPY1 vaccinated mice. Bacterial clearance and survival rates were decreased in SPY1 vaccinated IL-27Rα-/- mice. The vaccine-induced Th17 cell response and IgA secretion were also suppressed in IL-27Rα-/- mice. STAT3 and NF-κB signaling and expression of the Th17 cell polarization-related cytokines were also decreased in IL-27Rα-/- bone-marrow-derived dendritic cells(BMDC) stimulated with inactivated SPY1. The numbers of memory CD4+T cells were also decreased in SPY1 vaccinated IL-27Rα-/- mice. These results suggested that IL-27 plays a protective role in SPY1 vaccine by promoting Th17 polarization through STAT3 and NF-κB signaling pathways and memory CD4+T cells production in the SPY1 vaccine. In addition, we found that the immune protection of SPY1 vaccine was independent of aerobic glycolysis.

Suppressive effect of therapeutic antibiotic regimen on antipneumococcal Th1/Th17 responses in neonatal mice

BACKGROUND

Antibiotics are commonly used in human neonates, but their impact on neonatal T cell immunity remains poorly understood. The aim of this study was to investigate the impact of the antibiotic piperacillin with the beta-lactamase inhibitor tazobactam on neonatal CD4+ and CD8+ T cell responses to Streptococcus pneumoniae.

METHODS

Splenic and lung cells were isolated from the neonatal mice receiving piperacillin and tazobactam or saline (sham) and cultured with S. pneumoniae to analyze T cell cytokine production by ELISA and flow cytometry.

RESULTS

Antibiotic exposure to neonatal mice resulted in reduced numbers of CD4+/CD8+ T cells in the spleen and lungs compared to control mice. Upon in vitro stimulation with S. pneumoniae, splenocytes and lung cells from antibiotic-exposed mice produced lower levels of IFN-γ (Th1)/IL-17A (Th17) and IL-17A cytokines, respectively. Flow cytometric analysis revealed that S. pneumoniae-stimulated splenic CD4+ T cells from antibiotic-exposed mice expressed decreased levels of IFN-γ and IL-17A compared to control mice, whereas lung CD4+ T cells produced lower levels of IL-17A. However, no significant difference was observed for IL-4 (Th2) production.

CONCLUSIONS

Neonatal mice exposure to piperacillin and tazobactam reduces the number of CD4+ and CD8+ T cells, and suppresses Th1 and Th17, but not Th2, responses to S. pneumoniae.

IMPACT

Exposure of neonatal mice with a combination of piperacillin and tazobactam reduces CD4+/CD8+ T cells in the spleen and lungs. Antibiotic exposure suppresses neonatal Th1 and Th17, but not Th2, responses to Streptococcus pneumoniae. Our findings may have important implications for developing better therapeutic strategies in the neonatal intensive care unit.

Th17 Cells: Orchestrators of Mucosal Inflammation and Potential Therapeutic Targets

T helper 17 (Th17) cells represent a specialized subgroup of effector CD4+ T cells known for their role in provoking neutrophil-driven tissue inflammation, particularly within mucosal tissues. Although they are pivotal for defending the host against extracellular bacteria and fungi, they have also been associated with development of various T cell-mediated inflammatory conditions, autoimmune diseases, and even cancer. Notably, Th17 cells exhibit a dual nature, with different Th17 cell subtypes showcasing distinct effector functions and varying capacities to incite autoimmune tissue inflammation. Furthermore, Th17 cells exhibit significant plasticity, which carries important functional implications, both in terms of their expression of cytokines typically associated with other effector T cell subsets and in their interactions with regulatory CD4+ T cells. The intricate balance of Th17 cytokines can also be a double-edged sword in inflammation, autoimmunity, and cancer. Within this article, we delve into the mechanisms that govern the differentiation, function, and adaptability of Th17 cells. We culminate with an exploration of therapeutic potentials in harnessing the power of Th17 cells and their cytokines. Targeted interventions to modulate Th17 responses are emerging as promising strategies for autoimmunity, inflammation, and cancer treatment. By precisely fine-tuning Th17-related pathways, we may unlock new avenues for personalized therapeutic approaches, aiming to restore immune balance, alleviate the challenges of these disorders, and ultimately enhance the quality of life for individuals affected by them.

Influenza A Virus Exacerbates Group A Streptococcus Infection and Thwarts Anti-Bacterial Inflammatory Responses in Murine Macrophages

Seasonal influenza epidemics pose a considerable hazard for global health. In the past decades, accumulating evidence revealed that influenza A virus (IAV) renders the host vulnerable to bacterial superinfections which in turn are a major cause for morbidity and mortality. However, whether the impact of influenza on anti-bacterial innate immunity is restricted to the vicinity of the lung or systemically extends to remote sites is underexplored. We therefore sought to investigate intranasal infection of adult C57BL/6J mice with IAV H1N1 in combination with bacteremia elicited by intravenous application of Group A Streptococcus (GAS). Co-infection in vivo was supplemented in vitro by challenging murine bone marrow derived macrophages and exploring gene expression and cytokine secretion. Our results show that viral infection of mice caused mild disease and induced the depletion of CCL2 in the periphery. Influenza preceding GAS infection promoted the occurrence of paw edemas and was accompanied by exacerbated disease scores. In vitro co-infection of macrophages led to significantly elevated expression of TLR2 and CD80 compared to bacterial mono-infection, whereas CD163 and CD206 were downregulated. The GAS-inducible upregulation of inflammatory genes, such as Nos2, as well as the secretion of TNFα and IL-1β were notably reduced or even abrogated following co-infection. Our results indicate that IAV primes an innate immune layout that is inadequately equipped for bacterial clearance.

Long-term use of broad-spectrum antibiotics affects Ly6Chi monocyte recruitment and IL-17A and IL-22 production through the gut microbiota in tumor-bearing mice treated with chemotherapy

The protective effects of antibiotics against infection in cancer patients treated with chemotherapy remains unclear and related studies have been performed in healthy or pathogen-infected animal models. Here, we aimed to study the effects of antibiotic use on intestinal infection in tumor-bearing mice treated with chemotherapy and to determine the underlying mechanisms. Subcutaneous CT26 tumor-bearing mice were assigned to four groups: the control (Ctrl) group without any treatment, the antibiotic (ATB) group treated with a mixture of ampicillin, streptomycin, and colistin, the 5-fluorouracil (FU) group treated with four cycles of intraperitoneal injections of FU, and the ATB + FU group treated with the combination of ATB and FU. Gut microbial composition was determined and mesenteric lymph nodes (mLNs) were isolated for bacterial culturing. Intestinal permeability and integrity were assessed and the expression of cytokines was analyzed by quantitative PCR, ELISA, or flow cytometry (FCM). Monocytes in the colonic lamina propria (LP) were measured by FCM. Compared with the Ctrl and FU groups, the numbers of positive bacterial culturing results for mLNs were higher, and gut bacterial compositions were altered in the ATB and ATB + FU groups, with significantly decreased alpha diversity in the ATB + FU group. Intestinal integrity regarding the expression of tight junction proteins and intestinal permeability were not impaired significantly after treatments, but the colons were shorter in the ATB + FU group. The expression levels of intestinal IL-17A and IL-22, as well as the percentages of IL-17A⁺ cells in the colonic LP of the ATB + FU group, were lower than those in the FU group. The percentages of Ly6C^hi monocytes in the colonic LP were lower, but those in the spleen were higher in the ATB + FU group than in the FU group. The mRNA levels of colonic CCL8 were reduced in the ATB + FU group. Antibiotic use is associated with an increased incidence of intestinal infections in tumor-bearing mice treated with chemotherapy, which might in turn be associated with a dysregulated gut microbiota that inhibits colonic monocyte recruitment and IL-17A and IL-22 production.

IL-17 Cytokines and Chronic Lung Diseases

IL-17 cytokines are expressed by numerous cells (e.g., gamma delta (γδ) T, innate lymphoid (ILC), Th17, epithelial cells). They contribute to the elimination of bacteria through the induction of cytokines and chemokines which mediate the recruitment of inflammatory cells to the site of infection. However, IL-17-driven inflammation also likely promotes the progression of chronic lung diseases, such as chronic obstructive pulmonary disease (COPD), lung cancer, cystic fibrosis, and asthma. In this review, we highlight the role of IL-17 cytokines in chronic lung diseases.

Serotype-Dependent Effects on the Dynamics of Pneumococcal Colonization and Implications for Transmission

Capsule-switch mutants were compared to analyze how serotype affects the success of Streptococcus pneumoniae (Spn) during colonization and transmission. Strains of multiple serotypes were tested in highly susceptible infant mice, both singly and in competitive assays. Our findings demonstrated a role of serotype, apart from genetic background, in competitive success of strains, but this depended on timing postinoculation. As is the case for natural carriage, there was a hierarchy of success among serotypes using capsule-switch strains. The long-term dominance of a serotype was established within the first 4 h after acquisition, suggesting an effect independent of Spn-induced host responses. The hierarchy of serotype dominance correlated with decreased clearance rather than increased growth in vivo. Competitive assays staggering the timing of challenge showed that the first strain to dominate the niche sustained its competitive advantage, potentially explaining how increased density from delayed early clearance could result in serotype-dependent success. Effector molecules of intrastrain competition (fratricide), regulated by the competence operon in a quorum-sensing mechanism, were required for early niche dominance. This suggested a winner-takes-all scenario in which serotype is a major factor in achieving early niche dominance, such that once a strain reaches a threshold density it is able to exclude competitors through fratricide. Serotype was also an important determinant of transmission dynamics, although transit to a recipient host depended on effects of serotype different from its contribution to the dominance of colonization in the donor host. IMPORTANCE Capsule is the major virulence factor and surface antigen of the opportunistic respiratory pathogen Streptococcus pneumoniae (Spn). Strains of Spn express at least 100 structurally and immunologically distinct types (serotypes) of capsule, but for unknown reasons only a few are common. The effect of serotypes during the commensal interactions of Spn and its host, colonization and transmission, was tested. This was carried out by comparing genetically modified strains differing only in serotype in infant mouse models. Results show that serotype is an important factor in a strain's success during colonization. This was attributed to the effect of serotype on early clearance of the organism in the host. Competitive factors expressed by Spn (in a mechanism referred to as fratricide) allow the strain gaining this initial advantage to then dominate the upper respiratory tract niche. Serotype also plays an important role in a strain's success during transmission from one host to another.

<b><i>Streptococcus pneumoniae</i></b> Impairs Maturation of Human Dendritic Cells and Consequent Activation of CD4⁺ T Cells via Pneumolysin

Influenza A Virus (IAV), Staphylococcus aureus (staphylococci), and Streptococcus pneumoniae (pneumococci) are leading viral and bacterial causes of pneumonia. Dendritic cells (DCs) are present in the lower respiratory tract. They are characterized by low expression of co-stimulatory molecules, including CD80 and CD86 and high capacity of antigen uptake. Subsequently, DCs upregulate co-stimulatory signals and cytokine secretion to effectively induce T-cell priming. Here, we investigated these processes in response to bacterial and viral single as well as coinfections using human monocyte-derived (mo)DCs. Irrespective of single or coinfections, moDCs matured in response to IAV and/or staphylococcal infections, secreted a wide range of cytokines, and activated CD4⁺, CD8⁺ as well as double-negative T cells. In contrast, pneumococcal single and coinfections impaired moDC maturation, which was characterized by low expression of CD80 and CD86, downregulated expression of CD40, and a mild cytokine release resulting in abrogated CD4⁺ T-cell activation. These actions were attributed to the cholesterol-dependent cytotoxin pneumolysin (Ply). Infections with a ply-deficient mutant resulted in restored moDC maturation and exclusive CD4⁺ T-cell activation. These findings show that Ply has important immunomodulatory functions, supporting further investigations in specific modalities of Ply-DC interplay.

Synergism and Antagonism of Bacterial-Viral Coinfection in the Upper Respiratory Tract

Streptococcus pneumoniae (the pneumococcus) is a leading cause of pneumonia in children under 5 years of age. Coinfection by pneumococci and respiratory viruses enhances disease severity. Little is known about pneumococcal coinfections with respiratory syncytial virus (RSV). Here, we developed a novel infant mouse model of coinfection using pneumonia virus of mice (PVM), a murine analogue of RSV, to examine the dynamics of coinfection in the upper respiratory tract, an anatomical niche that is essential for host-to-host transmission and progression to disease. Coinfection increased damage to the nasal tissue and increased production of the chemokine CCL3. Nasopharyngeal pneumococcal density and shedding in nasal secretions were increased by coinfection. In contrast, coinfection reduced PVM loads in the nasopharynx, an effect that was independent of pneumococcal strain and the order of infection. We showed that this "antagonistic" effect was absent using either ethanol-killed pneumococci or a pneumococcal mutant deficient in capsule production and incapable of nasopharyngeal carriage. Colonization with a pneumococcal strain naturally unable to produce capsule also reduced viral loads. The pneumococcus-mediated reduction in PVM loads was caused by accelerated viral clearance from the nasopharynx. Although these synergistic and antagonistic effects occurred with both wild-type pneumococcal strains used in this study, the magnitude of the effects was strain dependent. Lastly, we showed that pneumococci can also antagonize influenza virus. Taken together, our study has uncovered multiple novel facets of bacterial-viral coinfection. Our findings have important public health implications, including for bacterial and viral vaccination strategies in young children. IMPORTANCE Respiratory bacterial-viral coinfections (such as pneumococci and influenza virus) are often synergistic, resulting in enhanced disease severity. Although colonization of the nasopharynx is the precursor to disease and transmission, little is known about bacterial-viral interactions that occur within this niche. In this study, we developed a novel mouse model to examine pneumococcal-viral interactions in the nasopharynx with pneumonia virus of mice (PVM) and influenza. We found that PVM infection benefits pneumococci by increasing their numbers in the nasopharynx and shedding of these bacteria in respiratory secretions. In contrast, we discovered that pneumococci decrease PVM numbers by accelerating viral clearance. We also report a similar effect of pneumococci on influenza. By showing that coinfections lead to both synergistic and antagonistic outcomes, our findings challenge the existing dogma in the field. Our work has important applications and implications for bacterial and viral vaccines that target these microbes.

Recent advances in development of nano-carriers for immunogene therapy in various complex disorders

Immunotherapy is a novel preference for the treatment of various complex diseases. Considering the application of varying agents for suppression or activation of the immune system, immunogene therapy was confirmed to stand as a proper alternative for other immunotherapeutic strategies due to its capability in targeting cells with more specificity that leads to controlling the expression of therapeutic genes. This method facilitates the local and single-dose application of most gene therapies that result in the usage of high therapeutic doses with a low risk of systemic side effects while being cost-efficient in long-term administrations. However, the existing barriers between the administration site and cell nucleus limited the clinical uses of genetic materials. These challenges can be overcome through the promising method of exerting non-carriers with high stability, low toxicity/immunogenicity, and simple modifications. In this study, we attempted to review the potential of nanoparticle application throughout the immunogene therapy of different diseases including cancer, microbial diseases, allergies, inflammatory bowel disease, rheumatoid arthritis, and respiratory infections. We included the outline of some challenges and opportunities in regards to the delivery of genetic materials that are based on nano-systems through immunotherapy of these disorders. Next to the promising future of these vectors, more detailed analyses are required to overcome the current limitations in clinical approaches.

Induction of T Cell Responses by Vaccination of a Streptococcus pneumoniae Whole-Cell Vaccine

The induction of T cell responses by vaccination is important for protection against infection. We have previously shown that immunization with a killed Streptococcus pneumoniae whole-cell vaccine (SPWCV) by either intranasal immunization or subcutaneous immunization induced T cell responses to SPWCV. Protection against colonization by S. pneumoniae is dependent on CD4+ IL-17A production induced by immunization. Here, we present detailed protocols for preparation of SPWCV, immunization of mice, and assay for T cell responses in blood and splenocytes in immunized mice.

Diminished Pneumococcal-Specific CD4+ T-Cell Response is Associated With Increased Regulatory T Cells at Older Age

Respiratory infection caused by Streptococcus pneumoniae is a leading cause of morbidity and mortality in older adults. Acquired CD4+ T cell mechanism are essential for the protection against colonization and subsequent development of infections by S. pneumoniae. In this study, we hypothesized that age-related changes within the CD4+ T-cell population compromise CD4+ T-cell specific responses to S. pneumoniae, thereby contributing to increased susceptibility at older age. To this end, we interrogated the CD4+ T-cell response against the immunogenic pneumococcal protein AliB, part of the unique oligopeptide ABC transporter system responsible for the uptake of nutrients for the bacterium and crucial for the development of pneumococcal meningitis, in healthy young and older adults. Specifically, proliferation of CD4+ T cells as well as concomitant cytokine profiles and phenotypic markers implied in immunosenescence were studied. Older adults showed decreased AliB-induced CD4+ T-cell proliferation that is associated with an increased frequency of regulatory T cells and lower levels of active CD25+CD127+CTLA-4−TIGIT-CD4+T cells. Additionally, levels of pro-inflammatory cytokines IFNy and IL-17F were decreased at older age. Our findings indicate that key features of a pneumococcal-specific CD4+ T-cell immune response are altered at older age, which may contribute to enhanced susceptibility for pneumococcal infections.

A TLR5 mono-agonist restores inhibited immune responses to Streptococcus pneumoniae during influenza virus infection in human monocytes

Influenza A virus (IAV) predisposes individuals to often more severe secondary bacterial infections with Streptococcus pneumonia (S. pneumoniae). The outcomes of these infections may be made worse with the increase in antimicrobial resistance and a lack of new treatments to combat this. Th17 responses are crucial in clearing S. pneumoniae from the lung. We previously demonstrated that early IAV infection of human monocytes significantly reduced levels of S. pneumoniae-driven cytokines involved in the Th17 response. Here, we have further identified that IAV targets specific TLRs (TLR2, TLR4, TLR9) involved in sensing S. pneumoniae infection resulting, in a reduction in TLR agonist-induced IL-23 and TGF-β. The effect of IAV is more profound on the TLR2 and TLR9 pathways. We have established that IAV-mediated inhibition of TLR9-induction is related to a downregulation of RORC, a Th17 specific transcription factor. Other studies using mouse models demonstrated that TLR5 agonism improved the efficacy of antibiotics in the treatment of IAV/S. pneumoniae co-infections. Therefore, we investigated if TLR5 agonism could restore inhibited Th17 responses in human monocytes. Levels of pneumococcus-driven cytokines, which had previously been inhibited by IAV were not reduced in the presence of the TLR5 mono-agonist, suggesting that such treatment may overcome IAV inhibition of Th17 responses. The importance of our research is in demonstrating the IAV directly targets S. pneumoniae-associated TLR pathways. Additionally, the IAV-inhibition of Th17 responses can be restored by TLR5 agonism, which indicates that there may be a different Th17 signalling pathway which is not affected by IAV infection.

Mycoplasma pneumoniae carriage evades induction of protective mucosal antibodies

Background

Mycoplasma pneumoniae is the most common bacterial cause of pneumonia in children hospitalised for community-acquired pneumonia (CAP). Prevention of infection by vaccines may be an important strategy in the presence of emerging macrolide-resistant M. pneumoniae. However, knowledge of immune responses to M. pneumoniae is limited, complicating vaccine design.

Methods

We studied the antibody response during M. pneumoniae respiratory tract infection and asymptomatic carriage in two different cohorts.

Results

In a nested case–control study (n=80) of M. pneumoniae carriers and matched controls we observed that carriage by M. pneumoniae does not lead to a rise in either mucosal or systemic M. pneumoniae-specific antibodies, even after months of persistent carriage. We replicated this finding in a second cohort (n=69) and also found that during M. pneumoniae CAP, mucosal levels of M. pneumoniae-specific IgA and IgG did increase significantly. In vitro adhesion assays revealed that high levels of M. pneumoniae-specific antibodies in nasal secretions of paediatric patients prevented the adhesion of M. pneumoniae to respiratory epithelial cells.

Conclusions

Our study demonstrates that M. pneumoniae-specific mucosal antibodies protect against bacterial adhesion to respiratory epithelial cells, and are induced only during M. pneumoniae infection and not during asymptomatic carriage. This is strikingly different from carriage with bacteria such as Streptococcus pneumoniae where mucosal antibodies are induced by bacterial carriage.

Antibodies against M. pneumoniae, the most common bacterial cause of pneumonia in children, are able to prevent adhesion of M. pneumoniae to epithelial cells, but are only induced during infection and not during asymptomatic carriagehttps://bit.ly/3CNdAhM

Neutrophil infiltration in co-housed littermates plays a key role in nasal transmission of Streptococcus pneumoniae in an infant mouse model

Transmission plays an important role in establishing pneumococcal colonization. It comprises three key events: shedding to transmit, entering into a susceptible new host, and adhering to the mucosal surface. Shedding of pneumococci from the respiratory tract of a colonized host is a pivotal step in transmission. Using a co-housed littermate mouse model, we evaluated the importance of the susceptibility to colonization of Streptococcus pneumoniae TIGR4 strain shed from index pups to non-colonized naïve contact pups. Despite sufficient pneumococcal shedding from the colonized host, S. pneumoniae was not contagious between littermates. Neutrophils infiltrated the nasal mucosa of contact pups and contributed to susceptibility of pneumococcal colonization during the course of transmission. Rejection of pneumococcal colonization in the contact pups was associated with accumulation of neutrophils in the nasal mucosa. Inflammation, characterized by neutrophil infiltration, prevents newly entering pneumococci from adhering to the respiratory epithelium in contact mice, suggesting that it plays an important role in reducing the rate of transmission in the initial response of naïve susceptible hosts to pneumococcal acquisition. The initial response of contact mice may regulate neutrophil and/or macrophage infiltration and control the acquisition of existing pneumococci.

Immunization with HMW1 and HMW2 adhesins protects against colonization by heterologous strains of nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is a common cause of localized respiratory tract disease and results in significant morbidity. The pathogenesis of NTHi disease begins with nasopharyngeal colonization, and therefore, the prevention of colonization represents a strategy to prevent disease. The NTHi HMW1 and HMW2 proteins are a family of conserved adhesins that are present in 75 to 80% of strains and have been demonstrated to play a critical role in colonization of the upper respiratory tract in rhesus macaques. In this study, we examined the vaccine potential of HMW1 and HMW2 using a mouse model of nasopharyngeal colonization. Immunization with HMW1 and HMW2 by either the subcutaneous or the intranasal route resulted in a strain-specific antibody response associated with agglutination of bacteria and restriction of bacterial adherence. Despite the specificity of the antibody response, immunization resulted in protection against colonization by both the parent NTHi strain and heterologous strains expressing distinct HMW1 and HMW2 proteins. Pretreatment with antibody against IL-17A eliminated protection against heterologous strains, indicating that heterologous protection is IL-17A dependent. This work demonstrates the vaccine potential of the HMW1 and HMW2 proteins and highlights the importance of IL-17A in protection against diverse NTHi strains.

Immunoadjunctive Therapy against Bacterial Infections Using Herbal Medicines Based on Th17 Cell-mediated Protective Immunity

One of the major health concerns in the world is the global increase in intractable bacterial infectious diseases due to the emergence of multi- and extensively drug-resistant bacterial pathogens as well as an increase in compromised hosts around the world. Particularly, in the case of mycobacteriosis, the high incidence of tuberculosis in developing countries, resurgence of tuberculosis in industrialized countries, and increase in the prevalence of Mycobacterium avium complex infections are important worldwide health concerns. However, the development of novel antimycobacterial drugs is currently making slow progress. Therefore, it is considered that devising improved administration protocols for clinical treatment against refractory mycobacteriosis using existing chemotherapeutics is more practical than awaiting the development of new antimycobacterial drugs. The regulation of host immune responses using immunoadjunctive agents may increase the efficacy of antimicrobial treatment against mycobacteriosis. The same situations also exist in cases of intractable infectious diseases due to common bacteria other than mycobacteria. The mild and long-term up-regulation of host immune reactions in hosts with intractable chronic bacterial infections, using herbal medicines and medicinal plants, may be beneficial for such immunoadjunctive therapy. This review describes the current status regarding basic and clinical studies on therapeutic regimens using herbal medicines, useful for the clinical treatment of patients with intractable bacterial infections. In particular, we focus on immunoadjunctive effects of herbal medicines on the establishment and manifestation of host antibacterial immunity related to the immunological roles of Th17 cell lineages.

Tissue-Specific Contributions to Control of T Cell Immunity

T cells are critical for orchestrating appropriate adaptive immune responses and maintaining homeostasis in the face of persistent nonpathogenic Ags. T cell function is controlled in part by environmental signals received upon activation and derived from the tissue environment in which Ag is encountered. Indeed, tissue-specific environments play important roles in controlling the T cell response to Ag, and recent evidence suggests that tissue draining lymph nodes can mirror those local differences. Thus, tissue-specific immunity may begin at priming in secondary lymph nodes, where local signals have an important role in T cell fate. In this study, we discuss the tissue-specific signals that may impact T cell differentiation and function, including the microbiome, metabolism, and tissue-specific innate cell imprinting. We argue that these individual contributions create tissue-specific niches that likely play important roles in T cell differentiation and function controlling the outcome of the response to Ags.

Insights Into the Effects of Mucosal Epithelial and Innate Immune Dysfunction in Older People on Host Interactions With Streptococcus pneumoniae

In humans, nasopharyngeal carriage of Streptococcus pneumoniae is common and although primarily asymptomatic, is a pre-requisite for pneumonia and invasive pneumococcal disease (IPD). Together, these kill over 500,000 people over the age of 70 years worldwide every year. Pneumococcal conjugate vaccines have been largely successful in reducing IPD in young children and have had considerable indirect impact in protection of older people in industrialized country settings (herd immunity). However, serotype replacement continues to threaten vulnerable populations, particularly older people in whom direct vaccine efficacy is reduced. The early control of pneumococcal colonization at the mucosal surface is mediated through a complex array of epithelial and innate immune cell interactions. Older people often display a state of chronic inflammation, which is associated with an increased mortality risk and has been termed 'Inflammageing'. In this review, we discuss the contribution of an altered microbiome, the impact of inflammageing on human epithelial and innate immunity to S. pneumoniae, and how the resulting dysregulation may affect the outcome of pneumococcal infection in older individuals. We describe the impact of the pneumococcal vaccine and highlight potential research approaches which may improve our understanding of respiratory mucosal immunity during pneumococcal colonization in older individuals.

Regulation and Function of ILC3s in Pulmonary Infections

Lower respiratory infections are among the leading causes of morbidity and mortality worldwide. These potentially deadly infections are further exacerbated due to the growing incidence of antimicrobial resistance. To combat these infections there is a need to better understand immune mechanisms that promote microbial clearance. This need in the context of lung infections has been further heightened with the emergence of SARS-CoV-2. Group 3 innate lymphoid cells (ILC3s) are a recently discovered tissue resident innate immune cell found at mucosal sites that respond rapidly in the event of an infection. ILC3s have clear roles in regulating mucosal immunity and tissue homeostasis in the intestine, though the immunological functions in lungs remain unclear. It has been demonstrated in both viral and bacterial pneumonia that stimulated ILC3s secrete the cytokines IL-17 and IL-22 to promote both microbial clearance as well as tissue repair. In this review, we will evaluate regulation of ILC3s during inflammation and discuss recent studies that examine ILC3 function in the context of both bacterial and viral pulmonary infections.

The expansive effects of polyamines on the metabolism and virulence of Streptococcus pneumoniae

Polyamines are common intracellular metabolites of nearly all cells, and their conservation across a vast diversity of cells suggests critical roles for these compounds in cellular physiology. Most intracellular polyamines are associated with RNA and, subsequently, polyamines have significant effects on transcription and translation. Putrescine and spermidine are the most common polyamines in bacteria. Intracellular polyamine pools in bacteria are tightly controlled by both de novo synthesis and transport. Polyamine homeostasis is emerging as a critical parameter of multiple pathways and physiology with substantial impact on bacterial pathogenesis, including the important human pathogen Streptococcus pneumoniae. Modulation of polyamine metabolism in pneumococci is an important regulator of central metabolism. It has broad effects on virulence factors such as capsule as well as stress responses that ultimately impact the survival of pneumococcus in a host. Polyamine transport protein as a single antigen or in combination with other pneumococcal proteins is shown to be an efficacious immunogen that protects against nasopharyngeal colonization, and invasive disease. A comprehensive description of polyamine metabolic pathways and their intersection with pneumococcal pathogenesis will undoubtedly point to novel approaches for treatment and prevention of pneumococcal disease.

Comparison of specific in-vitro virulence gene expression and innate host response in locally invasive vs colonizer strains of Streptococcus pneumoniae

Among Rochester NY children, a dramatic increase in nasopharyngeal (NP) colonization by non-vaccine pneumococcal serotypes 35B and 15A occurred during years 2010-2015, after introduction of 13-valent pneumococcal conjugate vaccine (PCV13). In our population, serotype 35B strains colonized in the nasopharynx (NP) but infrequently caused acute otitis media (AOM) whereas serotype 15A strains displayed virulence, evidenced by causing AOM. To explain the virulence difference, virulence genes expression between 35B and 15A, as well as the host's immune response during asymptomatic colonization were analyzed. We investigated differences in regulation of 19 virulence genes for differences in virulence using RT-PCR in 20 35B and 14 15A strains and measured gene expression of 9 host innate cytokines in the NP to assess the mucosal inflammatory response during asymptomatic colonization. Comparing 35B versus 15A strains, genes for competence ComA and RrgC were upregulated; capsular (Cps2D) and virulence genes (PfbA, PcpA and PhtE) were downregulated among 35B strains. PavB, LytA, LytB, NanA, CiaR, PhtD, LuxS, PspA and pneumolysin (Ply) showed no difference. IL17 and IL23 gene expression were > tenfold higher during 35B compared to 15A strain asymptomatic colonization. Only IL23 showed significant difference. In the first 5 years after introduction of PCV13, serotype 35B strains emerged as asymptomatic colonizers and 15A strains emerged to cause AOM in young children. Various genes (PfbA, PcpA, Cps2D and PhtE) among tested in this analysis were downregulated in 35B whereas ComA and RrgC were significantly upregulated. For the host's cytokine response, IL23 proinflammatory response which is essential for the differentiation of Th17 lymphocytes in the NP of children with 35B strains was significantly higher than the response to 15A during asymptomatic colonization.

Protective Effect of Nasal Colonisation with ∆cps/piaA and ∆cps/proABCStreptococcus pneumoniae Strains against Recolonisation and Invasive Infection

RATIONALE

Nasopharyngeal administration of live virulence-attenuated Streptococcus pneumoniae strains is a potential novel preventative strategy. One target for creating reduced virulence S. pneumoniae strains is the capsule, but loss of the capsule reduces the duration of S. pneumoniae colonisation in mice which could impair protective efficacy against subsequent infection.

OBJECTIVES

To assess protective efficacy of nasopharyngeal administration of unencapsulated S. pneumoniae strains in murine infection models.

METHODS

Strains containing cps locus deletions combined with the S. pneumoniae virulence factors psaA (reduces colonisation) or proABC (no effect on colonisation) were constructed and their virulence phenotypes and ability to prevent recolonisation or invasive infection assessed using mouse infection models. Serological responses to colonisation were compared between strains using ELISAs, immunoblots and 254 S. pneumoniae protein antigen array.

MEASUREMENTS AND MAIN RESULTS

The ∆cps/piaA and ∆cps/proABC strains were strongly attenuated in virulence in both invasive infection models and had a reduced ability to colonise the nasopharynx. ELISAs, immunoblots and protein arrays showed colonisation with either strain stimulated weaker serological responses than the wild type strain. Mice previously colonised with these strains were protected against septicaemic pneumonia but, unlike mice colonised with the wild type strain, not against S. pneumoniae recolonisation.

CONCLUSIONS

Colonisation with the ∆cps/piaA and ∆cps/proABC strains prevented subsequent septicaemia, but in contrast, to published data for encapsulated double mutant strains they did not prevent recolonisation with S. pneumoniae. These data suggest targeting the cps locus is a less effective option for creating live attenuated strains that prevent S. pneumoniae infections.

Repurposing Treatment of Wernicke-Korsakoff Syndrome for Th-17 Cell Immune Storm Syndrome and Neurological Symptoms in COVID-19: Thiamine Efficacy and Safety, In-Vitro Evidence and Pharmacokinetic Profile

Coronavirus disease identified in 2019 (COVID-19) can be complicated by the Th17 cell-mediated IL-17 proinflammatory response. We tested if thiamine can effectively lower the Th17 response in a clinical study [Proinflammatory state in alcohol use disorder patients termed as disease controls (DC)] and corroborated the results using an in vitro study. We developed an effective dose range and model for key pharmacokinetic measures with the potential of targeting the cytokine storm and neurological symptoms of COVID-19. Three-week 200 mg dose of thiamine was administered to sixteen DC patients. Eight healthy volunteers (HV) were also included in this investigation. A subsequent in vitro study was performed to validate the effectiveness of thiamine [100 mg/day equivalent (0.01 μg/ml)] treatment in lowering the Th17 proinflammatory response in a mouse macrophage cell line (RAW264.7) treated with ethanol. Based on recent publications, we compared the results of the IL-17 response from our clinical and in vitro study to those found in other proinflammatory disease conditions (metabolic conditions, septic shock, viral infections and COVID-19) and effective and safe dose ranges of thiamine. We developed a pharmacokinetic profile for thiamine dose range as a novel intervention strategy in COVID-19. DC group showed significantly elevated proinflammatory cytokines compared to HV. Thiamine-treated DC patients showed significant lowering in IL-17 and increase in the IL-22 levels. In humans, a range of 79-474 mg daily of thiamine was estimated to be effective and safe as an intervention for the COVID-19 cytokine storm. A literature review showed that several neurological symptoms of COVID-19 (∼45.5% of the severe cases) occur in other viral infections and neuroinflammatory states that may also respond to thiamine treatment. Thiamine, a very safe drug even at very high doses, could be repurposed for treating the Th17 mediated IL-17 immune storm, and the subsequent neurological symptoms observed in COVID-19. Further studies using thiamine as an intervention/prevention strategy in COVID-19 patients could identify its precise anti-inflammatory role.

IL-36 Cytokines Promote Inflammation in the Lungs of Long-Term Smokers

Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory lung disease with high morbidity and mortality. The IL-36 family are proinflammatory cytokines that are known to shape innate immune responses, including those critical to bacterial pneumonia. The objective of this study was to determine whether IL-36 cytokines promote a proinflammatory milieu in the lungs of long-term smokers with and without COPD. Concentrations of IL-36 cytokines were measured in plasma and BAL fluid from subjects in a pilot study (n = 23) of long-term smokers with and without COPD in vivo and from a variety of lung cells (from 3-5 donors) stimulated with bacteria or cigarette smoke components in vitro. Pulmonary macrophages were stimulated with IL-36 cytokines in vitro, and chemokine and cytokine production was assessed. IL-36α and IL-36γ are produced to varying degrees in murine and human lung cells in response to bacterial stimuli and cigarette smoke components in vitro. Moreover, whereas IL-36γ production is upregulated early after cigarette smoke stimulation and wanes over time, IL-36α production requires a longer duration of exposure. IL-36α and IL-36γ are enhanced systemically and locally in long-term smokers with and without COPD, and local IL-36α concentrations display a positive correlation with declining ventilatory lung function and increasing proinflammatory cytokine concentrations. In vitro, IL-36α and IL-36γ induce proinflammatory chemokines and cytokines in a concentration-dependent fashion that requires IL-36R and MyD88. IL-36 cytokine production is altered in long-term smokers with and without COPD and contributes to shaping a proinflammatory milieu in the lungs.

The Influence of B Cell Depletion Therapy on Naturally Acquired Immunity to Streptococcus pneumoniae

The anti-CD20 antibody Rituximab to deplete CD20+ B cells is an effective treatment for rheumatoid arthritis and B cell malignancies, but is associated with an increased incidence of respiratory infections. Using mouse models we have investigated the consequences of B cell depletion on natural and acquired humoral immunity to Streptococcus pneumoniae. B cell depletion of naïve C57Bl/6 mice reduced natural IgM recognition of S. pneumoniae, but did not increase susceptibility to S. pneumoniae pneumonia. ELISA and flow cytometry assays demonstrated significantly reduced IgG and IgM recognition of S. pneumoniae in sera from mice treated with B cell depletion prior to S. pneumoniae nasopharyngeal colonization compared to untreated mice. Colonization induced antibody responses to protein rather than capsular antigen, and when measured using a protein array B cell depletion prior to colonization reduced serum levels of IgG to several protein antigens. However, B cell depleted S. pneumoniae colonized mice were still partially protected against both lung infection and septicemia when challenged with S. pneumoniae after reconstitution of their B cells. These data indicate that although B cell depletion markedly impairs antibody recognition of S. pneumoniae in colonized mice, some protective immunity is maintained, perhaps mediated by cellular immunity.

Development of a Chimeric Vaccine Against Pseudomonas aeruginosa Based on the Th17-Stimulating Epitopes of PcrV and AmpC

Pulmonary infection caused by Pseudomonas aeruginosa (PA) has created an urgent need for an efficient vaccine, but the protection induced by current candidates is limited, partially because of the high variability of the PA genome. Antigens targeting pulmonary Th17 responses are able to provide antibody-independent and broad-spectrum protection; however, little information about Th17-stimulating antigens in PA is available. Herein, we identified two novel PA antigens that effectively induce Th17-dependent protection, namely, PcrV (PA1706) and AmpC (PA4110). Compared to intramuscular immunization, intranasal immunization enhanced the protection of rePcrV due to activation of a Th17 response. The Th17-stimulating epitopes of PcrV and AmpC were identified, and the recombinant protein PVAC was designed and generated by combining these Th17-stimulating epitopes. PVAC was successfully produced in soluble form and elicited broad protective immunity against PA. Our results provide an alternative strategy for the development of Th17-based vaccines against PA and other pathogens.

Experimental Human Challenge Defines Distinct Pneumococcal Kinetic Profiles and Mucosal Responses between Colonized and Non-Colonized Adults

Colonization of the upper respiratory tract with Streptococcus pneumoniae is the precursor of pneumococcal pneumonia and invasive disease. Following exposure, however, it is unclear which human immune mechanisms determine whether a pathogen will colonize. We used a human challenge model to investigate host-pathogen interactions in the first hours and days following intranasal exposure to Streptococcus pneumoniae Using a novel home sampling method, we measured early immune responses and bacterial density dynamics in the nose and saliva after volunteers were experimentally exposed to pneumococcus. Here, we show that nasal colonization can take up to 24 h to become established. Also, the following two distinct bacterial clearance profiles were associated with protection: nasal clearers with immediate clearance of bacteria in the nose by the activity of pre-existent mucosal neutrophils and saliva clearers with detectable pneumococcus in saliva at 1 h post challenge and delayed clearance mediated by an inflammatory response and increased neutrophil activity 24 h post bacterial encounter. This study describes, for the first time, how colonization with a bacterium is established in humans, signifying that the correlates of protection against pneumococcal colonization, which can be used to inform design and testing of novel vaccine candidates, could be valid for subsets of protected individuals.IMPORTANCE Occurrence of lower respiratory tract infections requires prior colonization of the upper respiratory tract with a pathogen. Most bacterial infection and colonization studies have been performed in murine and in vitro models due to the current invasive sampling methodology of the upper respiratory tract, both of which poorly reflect the complexity of host-pathogen interactions in the human nose. Self-collecting saliva and nasal lining fluid at home is a fast, low-cost, noninvasive, high-frequency sampling platform for continuous monitoring of bacterial encounter at defined time points relative to exposure. Our study demonstrates for the first time that, in humans, there are distinct profiles of pneumococcal colonization kinetics, distinguished by speed of appearance in saliva, local phagocytic function, and acute mucosal inflammatory responses, which may either recruit or activate neutrophils. These data are important for the design and testing of novel vaccine candidates.

The Role of NLRP3 Inflammasome in Pneumococcal Infections

Inflammasomes are innate immune sensors that regulate caspase-1 mediated inflammation in response to environmental, host- and pathogen-derived factors. The NLRP3 inflammasome is highly versatile as it is activated by a diverse range of stimuli. However, excessive or chronic inflammasome activation and subsequent interleukin-1β (IL-1β) release are implicated in the pathogenesis of various autoimmune diseases such as rheumatoid arthritis, inflammatory bowel disease, and diabetes. Accordingly, inflammasome inhibitor therapy has a therapeutic benefit in these diseases. In contrast, NLRP3 inflammasome is an important defense mechanism against microbial infections. IL-1β antagonizes bacterial invasion and dissemination. Unfortunately, patients receiving IL-1β or inflammasome inhibitors are reported to be at a disproportionate risk to experience invasive bacterial infections including pneumococcal infections. Pneumococci are typical colonizers of immunocompromised individuals and a leading cause of community-acquired pneumonia worldwide. Here, we summarize the current limited knowledge of inflammasome activation in pneumococcal infections of the respiratory tract and how inflammasome inhibition may benefit these infections in immunocompromised patients.

IL-10-producing NK cells exacerbate sublethal Streptococcus pneumoniae infection in the lung

Lung inflammation is tightly controlled to balance microbial clearance with the tissue damage that accompanies this response. Bacterial pathogens including Streptococcus pneumoniae (S. pneumoniae) modulate immune regulation by promoting secretion of the anti-inflammatory cytokine IL-10. The important cellular sources of IL-10 that impact protection against different bacterial infections are not well characterized. We find that S. pneumoniaeactivates IL-10 secretion from natural killer (NK) cells in the lung, which restrict host protection in a mouse model of sublethal infection. Direct transfer of wild-type NK cells into the lungs of IL-10-deficient mice drives bacterial expansion, identifying NK cells as a critical source of IL-10 promoting S. pneumoniae infection. The S. pneumoniae virulence protein Spr1875 was found to elicit NK cell IL-10 production in purified cells and in the lungs of live animals. These findings reveal therapeutic targets to combat bacterial-driven immune regulation in the lung.

Traditional Japanese Herbal Medicine Hochu-Ekki-to Promotes Pneumococcal Colonization Clearance via Macrophage Activation and Interleukin 17A Production in Mice

Streptococcus pneumoniae may colonize the nasopharynx, and as pneumococcal colonization causes invasive diseases and the subsequent transmission, reducing bacterial burden in the nasal cavity is critical. Hochu-ekki-to (TJ-41) is a traditional Japanese herbal medicine that exerts immunomodulatory effects in host cells. In this study, we investigated the potency of TJ-41 in modulating pneumococcal colonization clearance by activating host immunity. Mice, intranasally inoculated with pneumococci, were treated orally with TJ-41. During colonization, TJ-41 treatment significantly reduced pneumococcal burden and increased macrophage population in the nasopharynx. Furthermore, interleukin 17A production was significantly enhanced after TJ-41 treatment. In vitro experiment using nasal-derived cells revealed that pneumococcal antigen exposure upregulated the transcription of interleukin 17A in the TJ-41-treated group compared with that in the control group. Macrophages activated by killed bacteria were significantly increased in the presence of TJ-41 in an interleukin 17A-dependent manner. Moreover, TJ-41 enhanced phagocytosis, inhibited bacterial growth, and improved the antigen-presenting capacity of macrophages. Our results demonstrate that TJ-41 accelerates the clearance of pneumococcal nasopharyngeal colonization via macrophage activation. Subsequent production of interleukin 17A provides an additional benefit to effector cells.

Immune exclusion by naturally acquired secretory IgA against pneumococcal pilus-1

Successful infection by mucosal pathogens requires overcoming the mucus barrier. To better understand this key step, we performed a survey of the interactions between human respiratory mucus and the human pathogen Streptococcus pneumoniae. Pneumococcal adherence to adult human nasal fluid was seen only by isolates expressing pilus-1. Robust binding was independent of pilus-1 adhesive properties but required Fab-dependent recognition of RrgB, the pilus shaft protein, by naturally acquired secretory IgA (sIgA). Pilus-1 binding by specific sIgA led to bacterial agglutination, but adherence required interaction of agglutinated pneumococci and entrapment in mucus particles. To test the effect of these interactions in vivo, pneumococci were preincubated with human sIgA before intranasal challenge in a mouse model of colonization. sIgA treatment resulted in rapid immune exclusion of pilus-expressing pneumococci. Our findings predict that immune exclusion would select for nonpiliated isolates in individuals who acquired RrgB-specific sIgA from prior episodes of colonization with piliated strains. Accordingly, genomic data comparing isolates carried by mothers and their children showed that mothers are less likely to be colonized with pilus-expressing strains. Our study provides a specific example of immune exclusion involving naturally acquired antibody in the human host, a major factor driving pneumococcal adaptation.

Cortex Cercis chinensis Granules Attenuate Streptococcus pneumoniae Virulence by Targeting Pneumolysin

Pore-forming toxins produced by bacteria are some of the most important molecular weapons for bacterial virulence. Pneumolysin (PLY) is a pore-forming toxin secreted by Streptococcus pneumoniae (S. pneumoniae) and plays a vital role in the spread, colonization, and invasion of this bacterium in the host, indicating that PLY is a promising target for developing treatments against S. pneumoniae infection. In this study, Cortex Cercis chinensis granules (CCCGs), a prescription drug on the market, were shown to inhibit the pore-forming activity of PLY and protect against PLY-mediated cell hemolysis and A549 cell death without antibacterial activity or inhibition of PLY production. In addition, CCCG treatment inhibited the oligomerization of PLY. Animal experiments showed that CCCGs can reduce the death of mice infected with S. pneumoniae, the degree of pathological damage to the lungs, and the levels of TNF-α and IL-6 in the lungs. In summary, our results demonstrated that CCCGs, a marketed Chinese medicine, inhibit PLY activity and subsequently attenuate S. pneumoniae virulence, which would offer a novel strategy for fighting S. pneumoniae infection and a new use for CCCGs.

Lipidation of Pneumococcal Antigens Leads to Improved Immunogenicity and Protection

Streptococcus pneumoniae infections lead to high morbidity and mortality rates worldwide. Pneumococcal polysaccharide conjugate vaccines significantly reduce the burden of disease but have a limited range of protection, which encourages the development of a broadly protective protein-based alternative. We and others have shown that immunization with pneumococcal lipoproteins that lack the lipid anchor protects against colonization. Since immunity against S. pneumoniae is mediated through Toll-like receptor 2 signaling induced by lipidated proteins, we investigated the effects of a lipid modification on the induced immune responses in either intranasally or subcutaneously vaccinated mice. Here, we demonstrate that lipidation of recombinant lipoproteins DacB and PnrA strongly improves their immunogenicity. Mice immunized with lipidated proteins showed enhanced antibody concentrations and different induction kinetics. The induced humoral immune response was modulated by lipidation, indicated by increased IgG2/IgG1 subclass ratios related to Th1-type immunity. In a mouse model of colonization, immunization with lipidated antigens led to a moderate but consistent reduction of pneumococcal colonization as compared to the non-lipidated proteins, indicating that protein lipidation can improve the protective capacity of the coupled antigen. Thus, protein lipidation represents a promising approach for the development of a serotype-independent pneumococcal vaccine.

Immune Network Modeling Predicts Specific Nasopharyngeal and Peripheral Immune Dysregulation in Otitis-Prone Children

Acute otitis media (AOM) pathogenesis involves nasopharyngeal colonization by potential otopathogens and a viral co-infection. Stringently-defined otitis prone (sOP) children show characteristic patterns of immune dysfunction. We hypothesized that otitis proneness is largely a result of altered signaling between immune components that are otherwise competent, resulting in increased susceptibility to infection by bacterial otopathogens. To test this, we constructed a regulatory immune network model linking immune cells and signaling elements known to be involved in AOM and/or dysregulated in sOP children. The alignment of immune response mechanisms with data from in vivo and in vitro experimental observations produced 82 putative immune network models, each describing variants of immune regulatory networks consistent with available observations. Analysis of these models suggested that new measurements of serum levels of IL-4 and CXCL8 could refine competing models and resulted in the elimination of 38 of the models. Further analysis of the remaining 44 models suggested specific deviations in the predicted regulation of nasopharyngeal and peripheral immunity during response to AOM. Specifically, immune responses active in sOP children during AOM were characterized by early and constitutive activation of pro-inflammatory signaling in the nasopharynx and a Th2- and Treg-dominated profile in the periphery. We conclude that sOP children have altered regulation of key immune mediators during both health and pathogenesis. This altered regulation may be amenable to therapeutic intervention.

Double-Edged Role of Interleukin 17A in Streptococcus pneumoniae Pathogenesis During Influenza Virus Coinfection

BACKGROUND

We sought to determine the role of host interleukin 17A (IL-17A) response against colonizing Streptococcus pneumoniae, and its transition to a pathogen during coinfection with an influenza virus, influenza A H1N1 A/Puerto Rico/8/1934 (PR8).

METHOD

Wild-type (WT) C57BL/6 mice were intranasally inoculated with S. pneumoniae serotype 6A to establish colonization and later infected with the influenza strain, PR8, resulting in invasive S. pneumoniae disease. The role of the IL-17A response in colonization and coinfection was investigated in WT, RoRγt-/- and RAG1-/- mice with antibody-mediated depletion of IL-17A (WT) and CD90 cells (RAG1-/-).

RESULTS

RAG1-/- mice did not clear colonization and IL-17A neutralization impaired 6A clearance in WT mice. RoRγt-/- mice also had reduced clearance. S. pneumoniae-PR8 coinfection elicited a robust IL-17A response in the nasopharynx; IL-17A neutralization reduced S. pneumoniae invasive disease. RoRγt-/- mice also had reduced S. pneumoniae disease in a coinfection model. Depletion of CD90+ cells suppressed the IL-17A response and reduced S. pneumoniae invasion in RAG1-/- mice.

CONCLUSION

Our data show that although IL-17A reduces S. pneumoniae colonization, coinfection with influenza virus elicits a robust innate IL-17A response that promotes inflammation and S. pneumoniae disease in the nasopharynx.

Targeting Evolutionary Conserved Oxidative Stress and Immunometabolic Pathways for the Treatment of Respiratory Infectious Diseases

Significance: Up until recently, metabolism has scarcely been referenced in terms of immunology. However, emerging evidence has shown that immune cells undergo an adaptation of metabolic processes, known as the metabolic switch. This switch is key to the activation, and sustained inflammatory phenotype in immune cells, which includes the production of cytokines and reactive oxygen species (ROS) that underpin infectious diseases, respiratory and cardiovascular disease, neurodegenerative disease, as well as cancer. Recent Advances: There is a burgeoning body of evidence that immunometabolism and redox biology drive infectious diseases. For example, influenza A virus (IAV) utilizes endogenous ROS production via NADPH oxidase (NOX)2-containing NOXs and mitochondria to circumvent antiviral responses. These evolutionary conserved processes are promoted by glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle that drive inflammation. Such metabolic products involve succinate, which stimulates inflammation through ROS-dependent stabilization of hypoxia-inducible factor-1α, promoting interleukin-1β production by the inflammasome. In addition, itaconate has recently gained significant attention for its role as an anti-inflammatory and antioxidant metabolite of the TCA cycle. Critical Issues: The molecular mechanisms by which immunometabolism and ROS promote viral and bacterial pathology are largely unknown. This review will provide an overview of the current paradigms with an emphasis on the roles of immunometabolism and ROS in the context of IAV infection and secondary complications due to bacterial infection such as Streptococcus pneumoniae. Future Directions: Molecular targets based on metabolic cell processes and ROS generation may provide novel and effective therapeutic strategies for IAV and associated bacterial superinfections.

Efficacy of a Protein Vaccine and a Conjugate Vaccine Against Co-colonization with Vaccine-type and Non-vaccine Type Pneumococci in Mice

Widespread use of pneumococcal conjugate vaccines (PCVs) has led to substitution of vaccine-type (VT) strains by non-vaccine type (NVT) strains in nasopharyngeal carriage. We compared the efficacy of PCV13 and a nasal protein formulation containing pneumococcal surface protein A (PspA) adjuvanted with the whole-cell pertussis vaccine (wP) in the protection against co-colonization challenge models in mice with VT and NVT strains expressing different PspAs. Immunized mice were challenged with two different mixtures: i. VT4 (PspA3) + NVT33 (PspA1) and ii. VT23F (PspA2) + NVT15B/C (PspA4). Results from the first mixture showed a reduction in loads of VT4 strain in the nasopharynx of mice immunized with PCV13. A statistical difference between the loads of the VT and NVT strains was observed, indicating a competitive advantage for the NVT strain in PCV13-immunized animals. In the second mixture, no reduction was observed for the VT23F strain, probably due to low levels of anti-23F polysaccharide IgG induced by PCV13. Interestingly, a combination of the PspA formulation containing wP with PCV13 led to a reduction in colonization with both strains of the two mixtures tested, similar to the groups immunized nasally with wP or PspA plus wP. These results indicate that a combination of vaccines may be a useful strategy to overcome pneumococcal serotype replacement.

Immunologic dysfunction contributes to the otitis prone condition

Acute Otitis Media (AOM) is a multifactorial disease occurring mostly in young children who are immunologically naïve to AOM pathogens. This review focuses on work from Rochester NY, USA over the past 12 years among young children who had AOM infections microbiologically-confirmed by tympanocentesis, so called "stringently-defined". Among stringently-defined otitis prone children deficiencies in fundamental immune defense mechanisms have been identified that contribute to the propensity of young children to experience recurrent AOM. Dysfunction in innate immune responses that cause an immunopathological impact in the nasopharynx have been discovered including inadequate proinflammatory cytokine response and poor epithelial cell repair. Adaptive immunity defects in B cell function and immunologic memory resulting in low levels of antibody to otopathogen-specific antigens allows repeated infections. CD4+ and CD8+ T cell function and memory defects significantly contribute. The immune profile of an otitis prone child resembles that of a neonate through the first year of life. Immunologic deficits in otitis prone children cause them to be unusually vulnerable to viral upper respiratory infections and respond inadequately to routine pediatric vaccines.

Inflammation as a Modulator of Host Susceptibility to Pulmonary Influenza, Pneumococcal, and Co-Infections

Bacterial and viral pathogens are predominant causes of pulmonary infections and complications. Morbidity and mortality from these infections is increased in populations that include the elderly, infants, and individuals with genetic disorders such as Down syndrome. Immune senescence, concurrent infections, and other immune alterations occur in these susceptible populations, but the underlying mechanisms that dictate increased susceptibility to lung infections are not fully defined. Here, we review unique features of the lung as a mucosal epithelial tissue and aspects of inflammatory and immune responses in model pulmonary infections and co-infections by influenza virus and Streptococcus pneumoniae. In these models, lung inflammatory responses are a double-edged sword: recruitment of immune effectors is essential to eliminate bacteria and virus-infected cells, but inflammatory cytokines drive changes in the lung conducive to increased pathogen replication. Excessive accumulation of inflammatory cells also hinders lung function, possibly causing death of the host. Some animal studies have found that targeting host modulators of lung inflammatory responses has therapeutic or prophylactic effects in these infection and co-infection models. However, conflicting results from other studies suggest microbiota, sequence of colonization, or other unappreciated aspects of lung biology also play important roles in the outcome of infections. Regardless, a predisposition to excessive or aberrant inflammatory responses occurs in susceptible human populations. Hence, in appropriate contexts, modulation of inflammatory responses may prove effective for reducing the frequency or severity of pulmonary infections. However, there remain limitations in our understanding of how this might best be achieved—particularly in diverse human populations.

Respiratory Barrier as a Safeguard and Regulator of Defense Against Influenza A Virus and Streptococcus pneumoniae

The primary function of the respiratory system of gas exchange renders it vulnerable to environmental pathogens that circulate in the air. Physical and cellular barriers of the respiratory tract mucosal surface utilize a variety of strategies to obstruct microbe entry. Physical barrier defenses including the surface fluid replete with antimicrobials, neutralizing immunoglobulins, mucus, and the epithelial cell layer with rapidly beating cilia form a near impenetrable wall that separates the external environment from the internal soft tissue of the host. Resident leukocytes, primarily of the innate immune branch, also maintain airway integrity by constant surveillance and the maintenance of homeostasis through the release of cytokines and growth factors. Unfortunately, pathogens such as influenza virus and Streptococcus pneumoniae require hosts for their replication and dissemination, and prey on the respiratory tract as an ideal environment causing severe damage to the host during their invasion. In this review, we outline the host-pathogen interactions during influenza and post-influenza bacterial pneumonia with a focus on inter- and intra-cellular crosstalk important in pulmonary immune responses.

Phase variation in pneumococcal populations during carriage in the human nasopharynx

Streptococcus pneumoniae is one of the world's leading bacterial pathogens, responsible for pneumonia, septicaemia and meningitis. Asymptomatic colonisation of the nasopharynx is considered to be a prerequisite for these severe infections, however little is understood about the biological changes that permit the pneumococcus to switch from asymptomatic coloniser to invasive pathogen. A phase variable type I restriction-modification (R-M) system (SpnIII) has been linked to a change in capsule expression and to the ability to successfully colonise the murine nasopharynx. Using our laboratory data, we have developed a Markov change model that allows prediction of the expected level of phase variation within a population, and as a result measures when populations deviate from those expected at random. Using this model, we have analysed samples from the Experimental Human Pneumococcal Carriage (EHPC) project. Here we show, through mathematical modelling, that the patterns of dominant SpnIII alleles expressed in the human nasopharynx are significantly different than those predicted by stochastic switching alone. Our inter-disciplinary work demonstrates that the expression of alternative methylation patterns should be an important consideration in studies of pneumococcal colonisation.

IL-35 is critical in suppressing superantigenic Staphylococcus aureus-driven inflammatory Th17 responses in human nasopharynx-associated lymphoid tissue

The human nasopharynx is frequently exposed to microbial pathogens, including superantigen-producing Staphylococcus aureus (SAg-Sau), which activates potent pro-inflammatory T cell responses. However, cellular mechanisms that control SAg-Sau-driven T cell activation are poorly understood. Using human nasopharynx-associated lymphoid tissue (NALT), we show that SAg-Sau drove a strong Th17 activation, which was associated with an impaired CD4⁺ T cell-mediated immune regulation. This impairment of immune control correlated with a significant downregulation of interleukin-35 (IL-35) expression in tonsillar CD4⁺ T cells by SAg-Sau. Supplementing recombinant IL-35 suppressed SAg-Sau-activated Th17 responses, and this IL-35-mediated suppression positively correlated with the level of Th17 activation. Interestingly, SAg-Sau stimulation induced Foxp3⁺ Treg expansion and interleukin-10 (IL-10) production, which effectively suppressed the Th1 response, but failed to control the activation of Th17 cells. Overall, our results reveal an aberrant T cell regulation on SAg-Sau-driven Th17 activation and identify IL-35 as a critical cytokine to control superantigenic S.aureus-activated Th17 responses.

Generation of protective pneumococcal-specific nasal resident memory CD4+ T cells via parenteral immunization

The generation of tissue-resident memory T cells (T_RM) is an essential aspect of immunity at mucosal surfaces, and it has been suggested that preferential generation of T_RM is one of the principal advantages of mucosally administered vaccines. We have previously shown that antigen-specific, IL-17-producing CD4⁺ T cells can provide capsular antibody-independent protection against nasal carriage of Streptococcus pneumoniae; but whether pneumococcus-responsive T_RM are localized within the nasal mucosa and are sufficient for protection from carriage has not been determined. Here, we show that intranasal administration of live or killed pneumococci to mice generates pneumococcus-responsive IL-17A-producing CD4⁺ mucosal T_RM. Furthermore, we show that these cells are sufficient to mediate long-lived, neutrophil-dependent protection against subsequent pneumococcal nasal challenge. Unexpectedly, and in contrast with the prevailing paradigm, we found that parenteral administration of killed pneumococci also generates protective IL-17A⁺CD4⁺ T_RM in the nasal mucosa. These results demonstrate a critical and sufficient role of T_RM in prevention of pneumococcal colonization, and further that these cells can be generated by parenteral immunization. Our findings therefore have important implications regarding the generation of immune protection at mucosal surfaces by vaccination.

Differential IL-17A response to S. pneumoniae in adenoid tissue of children with sleep disordered breathing and otitis media with effusion

Streptococcus pneumonia, one of the major colonizers in nasopharyngeal adenoids, has been the predominant pathogen causing acute otitis media (AOM) in children. Recent evidence suggests an association between IL-17A-mediated immune response and the clearance of pneumococcal colonization in nasopharyngeal adenoids. Here, we evaluated the expressions of IL-17A and associated genes in hypertrophic adenoid tissues of children with sleep-disordered breathing (SDB) and otitis media with effusion (OME) and their association with pneumococcal carriage. Sixty-six pediatric patients with adenoid hypertrophy were enrolled. During adenoidectomy, nasopharyngeal swab and adenoid tissues were used to determine pneumococcal carriage and IL-17A expression. Our results revealed significantly higher levels of IL-17A and IL-17A:IL-10 mRNA in the SDB patients positive for nasopharyngeal pneumococcal carriage than those negative. However, these differences were not significant in the OME group. These results suggested, in OME patients, prolonged or chronic pneumococcal carriage may occur because of insufficient IL-17A-mediated mucosal clearance, and could further lead to AOM and OME development.