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

Efficacy of Mycobacterium indicus pranii immunotherapy as an adjunct to chemotherapy for tuberculosis and underlying immune responses in the lung

BACKGROUND

The 9-month-long chemotherapy of tuberculosis often results in poor compliance and emergence of drug-resistant strains. So, improved therapeutic strategy is urgently needed. Immunotherapy could be beneficial for the effective management of the disease. Previously we showed the protective efficacy of Mycobacterium indicus pranii (MIP) when given as prophylactic vaccine in animal models of tuberculosis.

METHODS

We sought to investigate whether MIP can be used as an adjunct to the chemotherapy in guinea pig models of tuberculosis. Efficacy of MIP was evaluated when given subcutaneously or by aerosol.

RESULTS

MIP-therapy as an adjunct to the chemotherapy was found to be effective in accelerating bacterial killing and improving organ pathology. MIP-immunotherapy resulted in higher numbers of activated antigen-presenting cells and lymphocytes in the infected lungs and also modulated the granulomatous response. Early increase in protective Th1 immune response was observed in the immunotherapy group. Following subsequent doses of MIP, decrease in the inflammatory response and increase in the immunosuppressive response was observed, which resulted in the improvement of lung pathology.

CONCLUSION

MIP immunotherapy is a valuable adjunct to chemotherapy for tuberculosis. Aerosol route of immunotherapy can play a crucial role for inducing immediate local immune response in the lung.

Monocytes regulate the mechanism of T-cell death by inducing Fas-mediated apoptosis during bacterial infection

Monocytes and T-cells are critical to the host response to acute bacterial infection but monocytes are primarily viewed as amplifying the inflammatory signal. The mechanisms of cell death regulating T-cell numbers at sites of infection are incompletely characterized. T-cell death in cultures of peripheral blood mononuclear cells (PBMC) showed 'classic' features of apoptosis following exposure to pneumococci. Conversely, purified CD3(+) T-cells cultured with pneumococci demonstrated necrosis with membrane permeabilization. The death of purified CD3(+) T-cells was not inhibited by necrostatin, but required the bacterial toxin pneumolysin. Apoptosis of CD3(+) T-cells in PBMC cultures required 'classical' CD14(+) monocytes, which enhanced T-cell activation. CD3(+) T-cell death was enhanced in HIV-seropositive individuals. Monocyte-mediated CD3(+) T-cell apoptotic death was Fas-dependent both in vitro and in vivo. In the early stages of the T-cell dependent host response to pneumococci reduced Fas ligand mediated T-cell apoptosis was associated with decreased bacterial clearance in the lung and increased bacteremia. In summary monocytes converted pathogen-associated necrosis into Fas-dependent apoptosis and regulated levels of activated T-cells at sites of acute bacterial infection. These changes were associated with enhanced bacterial clearance in the lung and reduced levels of invasive pneumococcal disease.

Controlled inflammatory responses in the lungs are associated with protection elicited by a pneumococcal surface protein A-based vaccine against a lethal respiratory challenge with Streptococcus pneumoniae in mice

Streptococcus pneumoniae is a pathogen of great importance worldwide. We have previously described the efficacy of a nasal vaccine composed of the pneumococcal surface protein A and the whole-cell pertussis vaccine as an adjuvant against a pneumococcal invasive challenge in mice. Spread of bacteria to the bloodstream was probably prevented by the high levels of systemic antibodies induced by the vaccine, but bacteria were only cleared from the lungs 3 weeks later, indicating that local immune responses may contribute to survival. Here we show that a strict control of inflammatory responses in lungs of vaccinated mice occurs even in the presence of high numbers of pneumococci. This response was characterized by a sharp peak of neutrophils and lymphocytes with a simultaneous decrease in macrophages in the respiratory mucosa at 12 h postchallenge. Secretion of interleukin-6 (IL-6) and gamma interferon (IFN-γ) was reduced at 24 h postchallenge, and the induction of tumor necrosis factor alpha (TNF-α) secretion, observed in the first hours postchallenge, was completely abolished at 24 h. Before challenge and at 12 h postchallenge, vaccinated mice displayed higher numbers of CD4(+) T, CD8(+) T, and B lymphocytes in the lungs. However, protection still occurs in the absence of each of these cells during the challenge, indicating that other effectors may be related to the prevention of lung injuries in this model. High levels of mucosal anti-PspA antibodies were maintained in vaccinated mice during the challenge, suggesting an important role in protection.

Marking and quantifying IL-17A-producing cells in vivo

Interleukin (IL)-17A plays an important role in host defense against a variety of pathogens and may also contribute to the pathogenesis of autoimmune diseases. However, precise identification and quantification of the cells that produce this cytokine in vivo have not been performed. We generated novel IL-17A reporter mice to investigate expression of IL-17A during Klebsiella pneumoniae infection and during experimental autoimmune encephalomyelitis, conditions previously demonstrated to potently induce IL-17A production. In both settings, the majority of IL-17A was produced by non-CD4(+) T cells, particularly γδ T cells, but also invariant NKT cells and other CD4(-)CD3ε(+) cells. As measured in dual-reporter mice, IFN-γ-producing Th1 cells greatly outnumbered IL-17A-producing Th17 cells throughout both challenges. Production of IL-17A by cells from unchallenged mice or by non-T cells under any condition was not evident. Administration of IL-1β and/or IL-23 elicited rapid production of IL-17A by γδ T cells, invariant NKT cells and other CD4(-)CD3ε(+) cells in vivo, demonstrating that these cells are poised for rapid cytokine production and likely comprise the major sources of this cytokine during acute immunologic challenges.

A decoy receptor 3 analogue reduces localised defects in phagocyte function in pneumococcal pneumonia

Background

Therapeutic strategies to modulate the host response to bacterial pneumonia are needed to improve outcomes during community-acquired pneumonia. This study used mice with impaired Fas signalling to examine susceptibility to pneumococcal pneumonia and decoy receptor 3 analogue (DcR3-a) to correct factors associated with increased susceptibility.

Methods

Wild-type mice and those with varying degrees of impairment of Fas (lpr) or Fas ligand signalling (gld) were challenged with Streptococcus pneumoniae and microbiological and immunological outcomes measured in the presence or absence of DcR3-a.

Results

During established pneumonia, neutrophils became the predominant cell in the airway and gld mice were less able to clear bacteria from the lungs, demonstrating localised impairment of pulmonary neutrophil function in comparison to lpr or wild-type mice. T-cells from gld mice had enhanced activation and reduced apoptosis in comparison to wild-type and lpr mice during established pneumonia. Treatment with DcR3-a reduced T-cell activation and corrected the defect in pulmonary bacterial clearance in gld mice.

Conclusions

The results suggest that imbalance in tumour necrosis factor superfamily signalling and excessive T-cell activation can impair bacterial clearance in the lung but that DcR3-a treatment can reduce T-cell activation, restore optimal pulmonary neutrophil function and enhance bacterial clearance during S pneumoniae infection.

Co-infection subverts mucosal immunity in the upper respiratory tract

Polymicrobial interactions on mucosal surfaces can influence inflammation, immunity, and disease outcome. Here, we review how host responses to colonization in the upper respiratory tract with the bacterial pathogen Streptococcus pneumoniae can be altered by co-infection. Recent advances provide a mechanistic understanding of how mucosal immunity can be subverted at distinct immunological time-points during pneumococcal colonization by other pathogens such as Haemophilus influenzae, influenza type A and Staphylococcus aureus. These examples use animal models of co-infection to highlight how otherwise effective host responses can be rendered ineffective by co-infection, and vice versa. The complex microbial ecology of mucosal sites must be considered to fully understand how immune responses in a natural setting influence the outcome of host-pathogen interactions.

Chemical inhibition of bacterial protein tyrosine phosphatase suppresses capsule production

Capsule polysaccharide is a major virulence factor for a wide range of bacterial pathogens, including Streptococcus pneumoniae. The biosynthesis of Wzy-dependent capsules in both gram-negative and -positive bacteria is regulated by a system involving a protein tyrosine phosphatase (PTP) and a protein tyrosine kinase. However, how the system functions is still controversial. In Streptococcus pneumoniae, a major human pathogen, the system is present in all but 2 of the 93 serotypes found to date. In order to study this regulation further, we performed a screen to find inhibitors of the phosphatase, CpsB. This led to the observation that a recently discovered marine sponge metabolite, fascioquinol E, inhibited CpsB phosphatase activity both in vitro and in vivo at concentrations that did not affect the growth of the bacteria. This inhibition resulted in decreased capsule synthesis in D39 and Type 1 S. pneumoniae. Furthermore, concentrations of Fascioquinol E that inhibited capsule also lead to increased attachment of pneumococci to a macrophage cell line, suggesting that this compound would inhibit the virulence of the pathogen. Interestingly, this compound also inhibited the phosphatase activity of the structurally unrelated gram-negative PTP, Wzb, which belongs to separate family of protein tyrosine phosphatases. Furthermore, incubation with Klebsiella pneumoniae, which contains a homologous phosphatase, resulted in decreased capsule synthesis. Taken together, these data provide evidence that PTPs are critical for Wzy-dependent capsule production across a spectrum of bacteria, and as such represents a valuable new molecular target for the development of anti-virulence antibacterials.

Contributions of capsule, lipoproteins and duration of colonisation towards the protective immunity of prior Streptococcus pneumoniae nasopharyngeal colonisation

Live attenuated vaccines have been proposed as a strategy to induce protective immunity against infectious diseases. Recent data have demonstrated that nasopharyngeal colonisation with Streptococcus pneumoniae induces protective immunity against subsequent invasive infection, suggesting nasal vaccination with live attenuated bacteria could be a preventative strategy. However the bacterial factors affecting the strength of this adaptive immune response remain unclear. In a direct comparison with the parent wild-type strain, we found that colonisation with bacteria lacking either capsule or surface lipoproteins led to significantly diminished protection. Immunity after colonisation was not dependent on serum IgG to capsular antigens. Colonisation density and duration was reduced for all the non-protective strains, suggesting that protective immunity maybe related to the extent of nasopharyngeal bacterial exposure. To investigate this hypothesis, we utilised an auxotrophic bacterial Δpab strain where duration of colonisation could be controlled by supply and removal of para-amino-benzoic acid (PABA) to mouse drinking water. Supporting colonisation with the Δpab strain for 5 days with PABA led to a faster serum antibody response compared to colonisation for less than 48 h. This enhanced immunogenicity was associated with a trend towards protection. The data presented here aid our understanding of why only certain live attenuated strains are able to function as effective vaccines, and may be valuable in informing the constituents of future live attenuated vaccines.

Characterization of Th17 responses to Streptococcus pneumoniae in humans: comparisons between adults and children in a developed and a developing country

Intranasal exposure to Streptococcus pneumoniae as well as mucosal or parenteral immunization with a recently developed killed pneumococcal whole cell vaccine, confer Th17-mediated protection against subsequent S. pneumoniae colonization in mice. Given our interest in the function of Th17 cells and the ongoing efforts to develop this vaccine for use in infants and children in developing countries, we analyzed Th17 responses to the whole cell antigen (WCA) and individual pneumococcal antigens in healthy individuals and patients with pneumococcal disease and compared responses in children and adults from Sweden and Bangladesh. Peripheral blood mononuclear cells (PBMCs) isolated from Swedish adults produced IL-17A after stimulation with WCA, with the pneumolysoid PdT and with the protein required for cell separation in group B streptococci (PcsB). IL-22 and IFN-γ responses were also detected, but these cytokines originated from separate CD4+ T cell subsets. PBMCs from Swedish children produced lower levels of IL-17A in response to WCA compared to adults, whereas no such difference was noted from the samples from Bangladesh, where responses by children and adults were both significantly higher than those in Sweden. High IL-17A responses to stimulation with WCA were also observed in children with proven or probable pneumococcal pneumonia. Our results thus demonstrate the presence of Th17-type T cells that are specific for pneumococcus in both children and adults. The different levels of Th17 responses to pneumococci in children and adults in developing and developed countries, which may at least partly be due to differences in exposure to pneumococci, are important factors to consider in the evaluation of candidate pneumococcal protein-based vaccines in human trials.

Human nasal challenge with Streptococcus pneumoniae is immunising in the absence of carriage

Infectious challenge of the human nasal mucosa elicits immune responses that determine the fate of the host-bacterial interaction; leading either to clearance, colonisation and/or disease. Persistent antigenic exposure from pneumococcal colonisation can induce both humoral and cellular defences that are protective against carriage and disease. We challenged healthy adults intra-nasally with live 23F or 6B Streptococcus pneumoniae in two sequential cohorts and collected nasal wash, bronchoalveolar lavage (BAL) and blood before and 6 weeks after challenge. We hypothesised that both cohorts would successfully become colonised but this did not occur except for one volunteer. The effect of bacterial challenge without colonisation in healthy adults has not been previously assessed. We measured the antigen-specific humoral and cellular immune responses in challenged but not colonised volunteers by ELISA and Flow Cytometry. Antigen-specific responses were seen in each compartment both before and after bacterial challenge for both cohorts. Antigen-specific IgG and IgA levels were significantly elevated in nasal wash 6 weeks after challenge compared to baseline. Immunoglobulin responses to pneumococci were directed towards various protein targets but not capsular polysaccharide. 23F but not 6B challenge elevated IgG anti-PspA in BAL. Serum immunoglobulins did not increase in response to challenge. In neither challenge cohort was there any alteration in the frequencies of TNF, IL-17 or IFNγ producing CD4 T cells before or after challenge in BAL or blood. We show that simple, low dose mucosal exposure with pneumococci may immunise mucosal surfaces by augmenting anti-protein immunoglobulin responses; but not capsular or cellular responses. We hypothesise that mucosal exposure alone may not replicate the systemic immunising effect of experimental or natural carriage in humans.

Exposure to respiratory pathogens such as Streptococcus pneumoniae (pneumococcus) is a frequent event that can result in immediate clearance, nasal colonisation or disease for the host. Human and mouse studies have shown that natural colonisation is an immunising event. Colonisation is prevalent in children but rare in human adults (<10%), suggesting that despite high pneumococcal exposure adult mucosal defences are sufficient to prevent colonisation. We exposed healthy adults to pneumococci in the nose in order to achieve colonisation and mimic a natural colonisation event. In most volunteers, however, we were not able to obtain colonisation using this protocol. In exposed but not colonised volunteers we measured antibody and cellular responses in nose, lung and blood samples. The mucosal defences elicited during acute pneumococcal exposure are poorly described but these data will shed light on the mechanisms that prevent colonisation in healthy adults and inform future vaccine design. Live bacterial exposure increases specific antibody and innate responses at mucosal surfaces such as the nose and lung. Systemic responses were not increased. These data suggest that acute bacterial exposure per se augments mucosal but not systemic defences. Natural or experimental colonisation may be required for systemic immunisation.

A bivalent vaccine to protect against Streptococcus pneumoniae and Salmonella typhi

Pneumococcal and Salmonella typhi infections are two major diseases for children in developing countries. For typhoid fever, licensed Vi polysaccharide vaccines are ineffective in children <2-year old. While investigational Vi conjugate vaccines have been shown effective in clinical trials, they are currently only available to restricted areas. Pneumococcal capsular polysaccharide conjugate vaccines are highly effective in children, but suffer from some limitations including cost and limited serotype coverage. We have previously shown that a fusion conjugate vaccine, consisting of pneumococcal fusion protein PsaA and pneumolysoid (PdT) conjugated to a polysaccharide, results in enhanced antibody and CD4+ Th17 cell responses as well as protection against pneumococcal colonization and disease in mice. Here we applied this approach to develop a bivalent vaccine against pneumococcus and S. typhi. Two species-conserved pneumococcal antigens (SP1572 or SP2070) were fused to the nonhemolytic pneumolysoid PdT. SP1572-PdT was then conjugated to Vi polysaccharide and SP2070-PdT was conjugated to the pneumococcal cell wall polysaccharide (CWPS; also conserved). Mice immunized with this bivalent conjugate were protected against pneumococcal colonization and sepsis challenges, and made anti-Vi antibody concentrations higher by 40-fold compared to mice that received equimolar mixtures of the antigens. An enhanced killing of Vi-bearing Salmonellae in vitro was demonstrated from plasma of mice that received the fusion conjugate but not the mixture of antigens. Our results support further evaluation of this bivalent immunogen for the prevention of pneumococcal colonization and disease, and of typhoid fever.

Divergent pro-inflammatory profile of human dendritic cells in response to commensal and pathogenic bacteria associated with the airway microbiota

Recent studies using culture-independent methods have characterized the human airway microbiota and report microbial communities distinct from other body sites. Changes in these airway bacterial communities appear to be associated with inflammatory lung disease, yet the pro-inflammatory properties of individual bacterial species are unknown. In this study, we compared the immune stimulatory capacity on human monocyte-derived dendritic cells (DCs) of selected airway commensal and pathogenic bacteria predominantly associated with lungs of asthma or COPD patients (pathogenic Haemophillus spp. and Moraxella spp.), healthy lungs (commensal Prevotella spp.) or both (commensal Veillonella spp. and Actinomyces spp.). All bacteria were found to induce activation of DCs as demonstrated by similar induction of CD83, CD40 and CD86 surface expression. However, asthma and COPD-associated pathogenic bacteria provoked a 3-5 fold higher production of IL-23, IL-12p70 and IL-10 cytokines compared to the commensal bacteria. Based on the differential cytokine production profiles, the studied airway bacteria could be segregated into three groups (Haemophilus spp. and Moraxella spp. vs. Prevotella spp. and Veillonella spp. vs. Actinomyces spp.) reflecting their pro-inflammatory effects on DCs. Co-culture experiments found that Prevotella spp. were able to reduce Haemophillus influenzae-induced IL-12p70 in DCs, whereas no effect was observed on IL-23 and IL-10 production. This study demonstrates intrinsic differences in DC stimulating properties of bacteria associated with the airway microbiota.

Immunization with Staphylococcus aureus iron regulated surface determinant B (IsdB) confers protection via Th17/IL17 pathway in a murine sepsis model

We have previously shown that IsdB, a conserved protein expressed by Staphylococcus aureus, induces a robust antibody response which correlates with protection in a murine challenge model. Here we investigate the role of cellular immunity in IsdB mediated protection using lymphocyte deficient SCID mice. As opposed to WT CB-17 mice the CB-17 SCID mice were not protected against a lethal challenge of S. aureus after active and passive immunizations with IsdB. Adoptive transfer of in vitro isolated lymphocyte subsets revealed that reconstituting mice with IsdB specific CD3+ or CD4+ T-cells conferred antigen specific protection while CD8⁺ T-cells, CD19⁺ B-cells and plasma cells (CD138^highB220^intCD19^lo) alone were not protective. A combination of CD3⁺ T-cells plus CD19⁺ B-cells conferred protection in CB-17 SCID mice, whereas bovine serum albumin (BSA) immune lymphocytes did not confer protection. Active immunization experiments indicated that IsdB immunized Jh mice (B-cell deficient) were protected against lethal challenge, while nude (T-cell deficient) mice were not. In vitro assays indicated that isolated IsdB specific splenocytes from immunized mice produced abundant IL-17A, much less IFN-γ and no detectable IL-4. IL-23 deficient mice were not protected from a lethal challenge by IsdB vaccination, pointing to a critical role for CD4⁺ Th17 in IsdB-mediated vaccination. Neutralizing IL-17A, but not IL-22 in vivo significantly increased mortality in IsdB immunized mice; whereas, neutralizing IFN-γ did not alter IsdB-mediated protection. These findings suggest that IL-17A producing Th17 cells play an essential role in IsdB vaccine-mediated defense against invasive S. aureus infection in mice.

Serotype-independent pneumococcal experimental vaccines that induce cellular as well as humoral immunity

For prevention of Streptococcus pneumoniae (pneumococcus) infections in infancy, protein-conjugated capsular polysaccharide vaccines provide serotype-specific, antibody-mediated immunity but do not cover all of the 90+ capsule serotypes. Therefore, microbiologists have sought protective noncapsular antigens common to all strains. Alternatively, we investigated killed cells of a noncapsulated strain, which expose many such common antigens. Given to mice intranasally, this vaccine elicits antibody-independent, CD4+ T lymphocyte-dependent accelerated clearance of pneumococci of various serotypes from the nasopharynx mediated by the cytokine IL-17A. Such immunity may reproduce the natural resistance that develops in infants before capsular antibodies arise. Given by injection, the killed cell vaccine induces bifunctional immunity: plasma antibodies protective against fatal pneumonia challenge, as well as IL-17A-mediated nasopharyngeal clearance. Human testing of this inexpensive candidate vaccine by intramuscular injection is planned. Bacterial cellular vaccines are complex--a challenge for reproducibility. However, when several known protective antigens were deleted, the killed pneumococcal vaccine was still protective. This antigenic redundancy may prevent vaccine escape variants by recombinational loss, which is frequent in pneumococcus. Biochemically defined immunogens with bifunctional activity have also been devised. These immunogens are three-component conjugates in which cell wall teichoic acid (a common antigen capable of T cell activation) is coupled to a genetic fusion of two common pneumococcal proteins: a protective surface antigen and a derivative of pneumolysin, which provides TLR4 agonist activity and induces antitoxic immunity. Such constructs induce accelerated clearance when given intranasally and induce both immune mechanisms when injected. The defined composition permits analysis of structure-function activity.

Inflammatory monocytes and neutrophils are licensed to kill during memory responses in vivo

Immunological memory is a hallmark of B and T lymphocytes that have undergone a previous encounter with a given antigen. It is assumed that memory cells mediate better protection of the host upon re-infection because of improved effector functions such as antibody production, cytotoxic activity and cytokine secretion. In contrast to cells of the adaptive immune system, innate immune cells are believed to exhibit a comparable functional effector response each time the same pathogen is encountered. Here, using mice infected by the intracellular bacterium Listeria monocytogenes, we show that during a recall bacterial infection, the chemokine CCL3 secreted by memory CD8⁺ T cells drives drastic modifications of the functional properties of several populations of phagocytes. We found that inflammatory ly6C⁺ monocytes and neutrophils largely mediated memory CD8⁺ T cell bacteriocidal activity by producing increased levels of reactive oxygen species (ROS), augmenting the pH of their phagosomes and inducing antimicrobial autophagy. These events allowed an extremely rapid control of bacterial growth in vivo and accounted for protective immunity. Therefore, our results provide evidence that cytotoxic memory CD8⁺ T cells can license distinct antimicrobial effector mechanisms of innate cells to efficiently clear pathogens.

The immune system comprises white blood cells that belong to the innate or the adaptive immune arms. Adaptive immune cells such as T and B lymphocytes can give rise to memory cells which mediate long-lived immunity against pathogens. During a recall infection, innate immune phagocytic cells such as monocytes and neutrophils can be critical to kill microbial pathogens inside infected tissues. Whether and how such antimicrobial features of phagocytic cells of the innate immune system are modulated during a memory response in a vaccinated host is not known. The present report shows that cytolytic memory T lymphocytes, an important subpopulation of effector T cells, can drastically enhance the functional killing capacities of monocytes and neutrophils for optimized pathogen clearance from infected hosts. These phagocytes exhibit enhanced generation of oxidative burst, increased phagosomal pH and autophagy, three mechanisms that lead to intracellular pathogen death. This result is important since it suggests that modulating innate immune cells effector activities could be an interesting strategy to enhance vaccine efficacy.

NO is a macrophage autonomous modifier of the cytokine response to streptococcal single-stranded RNA

Group B streptococci, a major cause of sepsis, induce inflammatory cytokines in strict dependence on bacterial ssRNA and the host molecules MyD88 and UNC-93B. In this study, we show that NO plays an important role in Group B streptococci-induced transcriptional activation of cytokine genes. Phagocytosis induced NO in a MyD88-dependent fashion. In turn, NO propagated the acidification of phagosomes and the processing of phagosomal bacterial nucleic acids and was required for potent transcriptional activation of cytokine genes by streptococci. This NO-dependent amplification loop has important mechanistic implications for the anti-streptococcal macrophage response and sepsis pathogenesis.

Roles of interleukin-17 in an experimental Legionella pneumophila pneumonia model

Interleukin-17 (IL-17) is a key factor in T helper type 17 (Th17) lineage host responses and plays critical roles in immunological control of a variety of infectious diseases. Although Legionella pneumophila, an intracellular bacterium found widely in the environment, often causes a serious and life-threatening pneumonia in humans, the contribution of IL-17 to immune function during Legionella pneumonia is unknown. In the present study, we used an experimental Legionella pneumonia infection to clarify the role of IL-17 in the resulting immune response. We observed robust production of pulmonary IL-17A and IL-17F (IL-17A/F), peaking on day 1 and declining thereafter. Upregulated production of tumor necrosis factor alpha (TNF-α), IL-6, and IL-1β, but not monocyte chemotactic protein 1 (MCP-1), was observed in Legionella-infected bone marrow-derived macrophages from BALB/c mice that had been stimulated with IL-17A or IL-17F. A significant decrease in the production of proinflammatory cytokines IL-6 and TNF-α was observed in IL-17A/F-deficient mice (BALB/c background) infected with L. pneumophila. Moreover, we found impaired neutrophil migration and lower numbers of chemokines (KC, LIX, and MIP-2) in IL-17A/F-deficient mice. IL-17A/F-deficient mice also eliminated L. pneumophila more slowly and were less likely to survive a lethal challenge. These results demonstrate that IL-17A/F plays a critical role in L. pneumophila pneumonia, probably through induction of proinflammatory cytokines and accumulation of neutrophils at the infection site.

Acquisition of pneumococci specific effector and regulatory Cd4+ T cells localising within human upper respiratory-tract mucosal lymphoid tissue

The upper respiratory tract mucosa is the location for commensal Streptococcus (S.) pneumoniae colonization and therefore represents a major site of contact between host and bacteria. The CD4⁺ T cell response to pneumococcus is increasingly recognised as an important mediator of immunity that protects against invasive disease, with data suggesting a critical role for Th17 cells in mucosal clearance. By assessing CD4 T cell proliferative responses we demonstrate age-related sequestration of Th1 and Th17 CD4⁺ T cells reactive to pneumococcal protein antigens within mucosal lymphoid tissue. CD25^hi T cell depletion and utilisation of pneumococcal specific MHCII tetramers revealed the presence of antigen specific Tregs that utilised CTLA-4 and PDL-1 surface molecules to suppress these responses. The balance between mucosal effector and regulatory CD4⁺ T cell immunity is likely to be critical to pneumococcal commensalism and the prevention of unwanted pathology associated with carriage. However, if dysregulated, such responses may render the host more susceptible to invasive pneumococcal infection and adversely affect the successful implementation of both polysaccharide-conjugate and novel protein-based pneumococcal vaccines.

The S. pneumoniae bacteria is a major cause of disease (e.g. pneumonia and meningitis) particularly affecting infants. In most cases bacteria can colonise the nose without causing harm, however colonisation is thought to be a prerequisite of disease. With increasing age colonization and disease, rates gradually decrease which is likely due to the development of immunity to the pneumococcus with age. The CD4 T cells of the immune system may contribute to the defence against bacterial colonisation by producing factors that promote pneumococcal killing. Herein, we show that CD4 T cells reactive to pneumococci are found in greater numbers at the site of colonisation and gradually increase in their levels from infancy. However, at the peak of CD4 T cell responses from late teens, we detected the presence of regulatory T cells (Tregs) which suppressed anti-pneumococci CD4 T cell activity greatly. Our finding shows that pneumococcal reactive CD4 T cells selectively populate colonisation sites and increase with age as a result of ongoing bacterial exposure throughout life, inversely correlating with colonisation and disease rates. As factors that utilise CD4 T cells become increasingly advocated as potential preventative strategies against pneumococcal carriage and disease, the observed effect of Tregs must be considered.

The Role of IL-17 in the Association between Pneumococcal Pneumonia and Allergic Sensitization

Interleukin- (IL-) 17 is important in the development of asthma and host defense against pneumococci. We determined the role of IL-17 in the risk of pneumococcal pneumonia. We challenged mice intranasally with a bioluminescent Streptococcus pneumoniae strain after sensitization and challenge with ovalbumin (OVA). We measured the levels of cytokines, including IL-17 (pg/mL), in the lung homogenate in experimental mice with and without OVA sensitization/challenge, as well as those with and without pneumococcal pneumonia. IL-17 levels were significantly lower in OVA-sensitized/challenged mice (9.69 ± 1.49), compared to the control mice (20.92 ± 1.82, P < 0.001). In our overall analysis, including IL-4 and IL-17 levels and OVA sensitization/challenge, IL-4 levels (OR: 81.9, 95%CI: 4.3-1523 per increment of 1.0 pg/mL, P = 0.003) were more significant than IL-17 levels (OR: 1.1, 95%CI: 1.03-1.17 per increment of 1.0 pg/mL, P = 0.003) in determining the risk of pneumococcal pneumonia. IL-17 levels result in a much smaller impact on the risk for pneumococcal pneumonia, compared to IL-4 levels.

The critical role of Notch ligand Delta-like 1 in the pathogenesis of influenza A virus (H1N1) infection

Influenza A viral infections have been identified as the etiologic agents for historic pandemics, and contribute to the annual mortality associated with acute viral pneumonia. While both innate and acquired immunity are important in combating influenza virus infection, the mechanism connecting these arms of the immune system remains unknown. Recent data have indicated that the Notch system is an important bridge between antigen-presenting cells (APCs) and T cell communication circuits and plays a central role in driving the immune system to overcome disease. In the present study, we examine the role of Notch signaling during influenza H1N1 virus infection, focusing on APCs. We demonstrate here that macrophages, but not dendritic cells (DCs), increased Notch ligand Delta-like 1 (Dll1) expression following influenza virus challenge. Dll1 expression on macrophages was dependent on retinoic acid-inducible gene-I (RIG-I) induced type-I IFN pathway, and not on the TLR3-TRIF pathway. We also found that IFNα-Receptor knockout mice failed to induce Dll1 expression on lung macrophages and had enhanced mortality during influenza virus infection. Our results further showed that specific neutralization of Dll1 during influenza virus challenge induced higher mortality, impaired viral clearance, and decreased levels of IFN-γ. In addition, we blocked Notch signaling by using γ-secretase inhibitor (GSI), a Notch signaling inhibitor. Intranasal administration of GSI during influenza infection also led to higher mortality, and higher virus load with excessive inflammation and an impaired production of IFN-γ in lungs. Moreover, Dll1 expression on macrophages specifically regulates IFN-γ levels from CD4⁺and CD8⁺T cells, which are important for anti-viral immunity. Together, the results of this study show that Dll1 positively influences the development of anti-viral immunity, and may provide mechanistic approaches for modifying and controlling the immune response against influenza H1N1 virus infection.

Influenza viruses cause annual epidemics and occasional pandemics that have claimed the lives of millions. Both innate and acquired immunity are essential for protection against influenza virus, and Notch and Notch ligands provide a key bridge between innate and acquired immunity. However, the role of Notch system during influenza virus infection is unknown. Here, we show that Notch ligand Delta-like 1 (Dll1) expression was up-regulated in influenza virus H1N1 challenged macrophages, and was dependent on both retinoic-acid–inducible protein I (RIG-I) and IFNα receptor (IFNαR)-mediated pathways. IFNαR-deficient mice challenged with influenza virus in vivo also display a profoundly impaired Dll1 expression with increased mortality and abrogated IFN-γ production. Treatment of WT mice during influenza infection, with either neutralizing antibodies specific for Dll1 or a γ-secretase inhibitor (GSI), which blocks Notch signaling, resulted in increased mortality, impaired viral clearance, and lower IFN-γ production. In addition, Dll1 specifically regulated IFN-γ production from both CD4⁺and CD8⁺T cells in vitro. Together, these results suggest that Notch signaling through macrophage-dependent Dll1 is critical in providing an anti-viral response during influenza infection by linking innate and acquired immunity.

Type I interferon response to extracellular bacteria in the airway epithelium

The airway epithelium possesses many mechanisms to prevent bacterial infection. Not only does it provide a physical barrier, but it also acts as an extension of the immune system through the expression of innate immune receptors and corresponding effectors. One outcome of innate signaling by the epithelium is the production of type I interferons (IFNs), which have traditionally been associated with activation via viral and intracellular organisms. We discuss how three extracellular bacterial pathogens of the airway activate this intracellular signaling cascade through both surface components as well as via secretion systems, and the differing effects of type I IFN signaling on host defense of the respiratory tract.

Protective contributions against invasive Streptococcus pneumoniae pneumonia of antibody and Th17-cell responses to nasopharyngeal colonisation

The nasopharyngeal commensal bacteria Streptococcus pneumoniae is also a frequent cause of serious infections. Nasopharyngeal colonisation with S. pneumoniae inhibits subsequent re-colonisation by inducing Th17-cell adaptive responses, whereas vaccination prevents invasive infections by inducing antibodies to S. pneumoniae capsular polysaccharides. In contrast, protection against invasive infection after nasopharyngeal colonisation with mutant S. pneumoniae strains was associated with antibody responses to protein antigens. The role of colonisation-induced Th17-cell responses during subsequent invasive infections is unknown. Using mouse models, we show that previous colonisation with S. pneumoniae protects against subsequent lethal pneumonia mainly by preventing bacteraemia with a more modest effect on local control of infection within the lung. Previous colonisation resulted in CD4-dependent increased levels of Th17-cell cytokines during subsequent infectious challenge. However, mice depleted of CD4 cells prior to challenge remained protected against bacteraemia, whereas no protection was seen in antibody deficient mice and similar protection could be achieved through passive transfer of serum. Serum from colonised mice but not antibody deficient mice promoted phagocytosis of S. pneumoniae, and previously colonised mice were able to rapidly clear S. pneumoniae from the blood after intravenous inoculation. Thus, despite priming for a Th17-cell response during subsequent infection, the protective effects of prior colonisation in this model was not dependent on CD4 cells but on rapid clearance of bacteria from the blood by antibody-mediated phagocytosis. These data suggest that whilst nasopharyngeal colonisation induces a range of immune responses, the effective protective responses depend upon the site of subsequent infection.

Infection with conditionally virulent Streptococcus pneumoniae Δpab strains induces antibody to conserved protein antigens but does not protect against systemic infection with heterologous strains

Avirulent strains of a bacterial pathogen could be useful tools for investigating immunological responses to infection and potentially effective vaccines. We have therefore constructed an auxotrophic TIGR4 Δpab strain of Streptococcus pneumoniae by deleting the pabB gene Sp_0665. The TIGR4 Δpab strain grew well in complete medium but was unable to grow in serum unless it was supplemented with para-aminobenzoic acid (PABA). The TIGR4 Δpab strain was markedly attenuated in virulence in mouse models of S. pneumoniae nasopharyngeal colonization, pneumonia, and sepsis. Supplementing mouse drinking water with PABA largely restored the virulence of TIGR4 Δpab. An additional Δpab strain constructed in the D39 capsular serotype 2 background was also avirulent in a sepsis model. Systemic inoculation of mice with TIGR4 Δpab induced antibody responses to S. pneumoniae protein antigens, including PpmA, PsaA, pneumolysin, and CbpD, but not capsular polysaccharide. Flow cytometry demonstrated that IgG in sera from TIGR4 Δpab-vaccinated mice bound to the surface of TIGR4 and D39 bacteria but not to a capsular serotype 3 strain, strain 0100993. Mice vaccinated with the TIGR4 Δpab or D39 Δpab strain by intraperitoneal inoculation were protected from developing septicemia when challenged with the homologous S. pneumoniae strain. Vaccination with the TIGR4 Δpab strain provided only weak or no protection against heterologous challenge with the D39 or 0100993 strain but did strongly protect against a TIGR4 capsular-switch strain expressing a serotype 2 capsule. The failure of cross-protection after systemic vaccination with Δpab bacteria suggests that parenteral administration of a live attenuated vaccine is not an attractive approach for preventing S. pneumoniae infection.

Intestinal epithelial cells modulate CD4 T cell responses via the thymus leukemia antigen

The intestinal epithelium is comprised of a monolayer of intestinal epithelial cells (IEC), which provide, among other functions, a physical barrier between the high Ag content of the intestinal lumen and the sterile environment beyond the epithelium. IEC express a nonclassical MHC class I molecule known as the thymus leukemia (TL) Ag. TL is known to interact with CD8αα-expressing cells, which are abundant in the intestinal intraepithelial lymphocyte compartment. In this report, we provide evidence indicating that expression of TL by IEC modulates the cytokine profile of CD4(+) T cells favoring IL-17 production. We show in an adoptive transfer model of colitis that donor-derived cells become more pathogenic when TL is expressed on IEC in recipient animals. Moreover, TL(+)IEC promote development of IL-17-mediated responses capable of protecting mice from Citrobacter rodentium infection. We also show that modulation of IL-17-mediated responses by TL(+)IEC is controlled by the expression of CD8α on CD4(+) T cells. Overall, our results provide evidence for an important interaction between IEC and CD4(+) T cells via TL, which modulates mucosal immune responses.

Synergistic stimulation of type I interferons during influenza virus coinfection promotes Streptococcus pneumoniae colonization in mice

Pneumococcal infection of the respiratory tract is often secondary to recent influenza virus infection and accounts for much of the morbidity and mortality during seasonal and pandemic influenza. Here, we show that coinfection of the upper respiratory tract of mice with influenza virus and pneumococcus leads to synergistic stimulation of type I IFNs and that this impairs the recruitment of macrophages, which are required for pneumococcal clearance, due to decreased production of the chemokine CCL2. Type I IFN expression was induced by pneumococcal colonization alone. Colonization followed by influenza coinfection led to a synergistic type I IFN response, resulting in increased density of colonizing bacteria and susceptibility to invasive infection. This enhanced type I IFN response inhibited production of the chemokine CCL2, which promotes the recruitment of macrophages and bacterial clearance. Stimulation of CCL2 by macrophages upon pneumococcal infection alone required the pattern recognition receptor Nod2 and expression of the pore-forming toxin pneumolysin. Indeed, the increased colonization associated with concurrent influenza virus infection was not observed in mice lacking Nod2 or the type I IFN receptor, or in mice challenged with pneumococci lacking pneumolysin. We therefore propose that the synergistic stimulation of type I IFN production during concurrent influenza virus and pneumococcal infection leads to increased bacterial colonization and suggest that this may contribute to the higher rates of disease associated with coinfection in humans.

Nod2 sensing of lysozyme-digested peptidoglycan promotes macrophage recruitment and clearance of S. pneumoniae colonization in mice

Streptococcus pneumoniae colonizes the mucosal surface of the human upper respiratory tract. A colonization event is gradually cleared through phagocytosis by monocytes/macrophages that are recruited to the airway lumen. Here, we sought to define the bacterial and host factors that promote monocyte/macrophage influx and S. pneumoniae clearance using intranasal bacterial challenge in mice. We found that the recruitment of monocytes/macrophages required their expression of the chemokine receptor CCR2 and correlated with expression of the CCR2 ligand CCL2. Production of CCL2 and monocyte/macrophage recruitment were deficient in mice lacking digestion of peptidoglycan by lysozyme (LysM) and cytosolic sensing of the products of digestion by Nod2. Ex vivo macrophages produced CCL2 following bacterial uptake, digestion by LysM, and sensing of peptidoglycan by Nod2. Sensing of digested peptidoglycan by Nod2 also required the pore-forming toxin pneumolysin. The generation of an adaptive immune response, as measured by anti-pneumococcal antibody titers, was also LysM- and Nod2-dependent. Together, our data suggest that bacterial uptake by professional phagocytes is followed by LysM-mediated digestion of S. pneumoniae-derived peptidoglycan, sensing of the resulting products by Nod2, release of the chemokine CCL2, and CCR2-dependent recruitment of the additional monocytes/macrophages required for the clearance of an S. pneumoniae colonization event.

Invasive bacterial pathogens exploit TLR-mediated downregulation of tight junction components to facilitate translocation across the epithelium

Streptococcus pneumoniae and Haemophilus influenzae are members of the normal human nasal microbiota with the ability to cause invasive infections. Bacterial invasion requires translocation across the epithelium; however, mechanistic understanding of this process is limited. Examining the epithelial response to murine colonization by S. pneumoniae and H. influenzae, we observed the TLR-dependent downregulation of claudins 7 and 10, tight junction components key to the maintenance of epithelial barrier integrity. When modeled in vitro, claudin downregulation was preceded by upregulation of SNAIL1, a transcriptional repressor of tight junction components, and these phenomena required p38 MAPK and TGF-β signaling. Consequently, downregulation of SNAIL1 expression inhibited bacterial translocation across the epithelium. Furthermore, disruption of epithelial barrier integrity by claudin 7 inhibition in vitro or TLR stimulation in vivo promoted bacterial translocation. These data support a general mechanism for epithelial opening exploited by invasive pathogens to facilitate movement across the epithelium to initiate disease.

The innate immune response to Streptococcus pneumoniae in the lung depends on serotype and host response

Bacteremic pneumonia with some pneumococcal capsular serotypes, including serotype 3 (ST3), has been associated with a higher risk of death, whereas others, such as ST8, are associated with a lower risk. To provide a molecular basis for understanding such differences, we used oligo cDNA microarrays to analyze and compare the gene expression profiles of the lungs of Balb/c mice infected intranasally with either ST3, strain A66.1, or ST8, strain ATCC 6308 (6308). Compared to uninfected controls, infection with either A66.1 or 6308 led to inoculum-dependent expression of IFN-γ inducible CXC chemokines among other pro-inflammatory genes. To investigate the role that IFN-γ inducible chemokines CXCL9, CXCL10 and CXCL11 play in A66.1- and 6308-induced pneumonia, we examined the effect of the absence of their common receptor, CXCR3, on intranasal infection in CXCR3(-/-) (Balb/c) mice. Compared to wild type (WT) mice, virulence of A66.1 but not 6308 was attenuated in CXCR3(-/-) mice. A66.1-infected CXCR3(-/-) mice had fewer lung neutrophils and more alveolar macrophages 48 h after infection and fewer blood CFU 72 h after infection. Histopathological examination of lung sections revealed less inflammation among A66.1-infected CXCR3(-/-) than WT mice. The reduced virulence of A66.1 in CXCR3(-/-) mice suggests that inhibition of the functional activity of IFN-γ inducible chemokines modulates the host response to A66.1, in turn suggesting a novel approach to improve vaccine-mediated protection against ST3 pneumonia.

The natural cytotoxicity receptor 1 contribution to early clearance of Streptococcus pneumoniae and to natural killer-macrophage cross talk

Natural killer (NK) cells serve as a crucial first line of defense against tumors, viral and bacterial infections. We studied the involvement of a principal activating natural killer cell receptor, natural cytotoxicity receptor 1 (NCR1), in the innate immune response to S. pneumoniae infection. Our results demonstrate that the presence of the NCR1 receptor is imperative for the early clearance of S. pneumoniae. We tied the ends in vivo by showing that deficiency in NCR1 resulted in reduced lung NK cell activation and lung IFNγ production at the early stages of S. pneumoniae infection. NCR1 did not mediate direct recognition of S. pneumoniae. Therefore, we studied the involvement of lung macrophages and dendritic cells (DC) as the mediators of NK-expressed NCR1 involvement in response to S. pneumoniae. In vitro, wild type BM-derived macrophages and DC expressed ligands to NCR1 and co-incubation of S. pneumoniae-infected macrophages/DC with NCR1-deficient NK cells resulted in significantly lesser IFNγ levels compared to NCR1-expressing NK cells. In vivo, ablation of lung macrophages and DC was detrimental to the early clearance of S. pneumoniae. NCR1-expressing mice had more potent alveolar macrophages as compared to NCR1-deficient mice. This result correlated with the higher fraction of NCR1-ligand^high lung macrophages, in NCR1-expressing mice, that had better phagocytic activity compared to NCR1-ligand^dull macrophages. Overall, our results point to the essential contribution of NK-expressed NCR1 in early response to S. pneumoniae infection and to NCR1-mediated interaction of NK and S. pneumoniae infected-macrophages and -DC.

Host immunity in the protective response to nasal immunization with a pneumococcal antigen associated to live and heat-killed Lactobacillus casei

Background

At present, available pneumococcal vaccines have failed to eradicate infections caused by S. pneumoniae. Search for effective vaccine continues and some serotype independent pneumococcal proteins are considered as candidates for the design of new vaccines, especially a mucosal vaccine, since pneumococci enter the body through mucosal surfaces. Selection of the appropriate adjuvant is important for mucosal vaccines, and lactic acid bacteria (LAB) with immunostimulant properties are promissory candidates. In this work, we assessed the adjuvant effect of a probiotic strain, Lactobacillus casei (L. casei), when nasally administered with a pneumococcal antigen (pneumococcal protective protein A: PppA) for the prevention of pneumococcal infection. Adjuvanticity of both live (LcV) and heat-killed (LcM) was evaluated and humoral and cellular antigen-specific immune response was assessed in mucosal and systemic compartments. The potential mechanisms induced by nasal immunization were discussed.

Results

Nasal immunization of young mice with PppA+LcV and PppA+LcM induced anti-PppA IgA and IgG antibodies in mucosal and systemic compartments and levels of these specific antibodies remained high even at day 45 after the 3rd Immunization (3rd I). These results were correlated with IL-4 induction by the mixture of antigen plus LcV and LcM. Also, PppA+Lc (V and M) induced stimulation of Th1 and Th17 cells involved in the defence against pneumococci. The protection against pneumococcal respiratory challenge at day 30 after the 3rd I showed that PppA+LcV and PppA+LcM immunizations significantly reduced pathogen counts in nasal lavages while prventing their passage into lung and blood. Survival of mice immunized with the co-application of PppA plus LcV and LcM was significantly higher than in mice immunized with PppA alone and control mice when intraperitoneal challenge was performed. No significant differences between the treatments involving LcV and LcM were found.

Conclusions

Live and heat-killed L. casei enhanced the antigen-specific immune response when administered nasally with a pneumococcal antigen. Considering the potential risk associated with live bacteria, the design of a nasal vaccine based on pneumococcal antigens and heat-killed L. casei emerges as a safe and effective strategy for the prevention of pneumococcal infections and opens new possibilities of application of dead LAB as adjuvants in vaccine formulations against other pathogens.

Formulation of a killed whole cell pneumococcus vaccine - effect of aluminum adjuvants on the antibody and IL-17 response

Background

Streptococcus pneumoniae causes widespread morbidity and mortality. Current vaccines contain free polysaccharides or protein-polysaccharide conjugates, and do not induce protection against serotypes that are not included in the vaccines. An affordable and broadly protective vaccine is very desirable. The goal of this study was to determine the optimal formulation of a killed whole cell pneumococcal vaccine with aluminum-containing adjuvants for intramuscular injection.

Methods

Four aluminium-containing adjuvants were prepared with different levels of surface phosphate groups resulting in different adsorptive capacities and affinities for the vaccine antigens. Mice were immunized three times and the antigen-specific antibody titers and IL-17 responses in blood were analyzed.

Results

Although all adjuvants induced significantly higher antibody titers than antigen without adjuvant, the vaccine containing aluminum phosphate adjuvant (AP) produced the highest antibody response when low doses of antigen were used. Aluminum hydroxide adjuvant (AH) induced an equal or better antibody response at high doses compared with AP. Vaccines formulated with AH, but not with AP, induced an IL-17 response. The vaccine formulated with AH was stable and retained full immunogenicity when stored at 4°C for 4 months.

Conclusions

Antibodies are important for protection against systemic streptococcal disease and IL-17 is critical in the prevention of nasopharyngeal colonization by S. pneumoniae in the mouse model. The formulation of the whole killed bacterial cells with AH resulted in a stable vaccine that induced both antibodies and an IL-17 response. These experiments underscore the importance of formulation studies with aluminium containing adjuvants for the development of stable and effective vaccines.

Human monocytes promote Th1 and Th17 responses to Streptococcus pneumoniae

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and sepsis in children. Human immunity to pneumococcal infections has been assumed to depend on anticapsular antibodies. However, recent findings from murine models suggest that alternative mechanisms, dependent on T helper cells, are also involved. Although the immunological events in which T helper cells contribute to acquired immunity have been studied in mice, little is known about how these responses are generated in humans. Therefore, we examined bacterial and host factors involved in the induction of Th1 and Th17 responses, using a coculture model of human monocytes and CD4(+) T cells. We show that monocytes promote effector cytokine production by memory T helper cells, leading to a mixed Th1/Th17 (gamma interferon [IFN-γ]/interleukin-17 [IL-17]) profile. Both T helper cytokines were triggered by purified pneumococcal peptidoglycan; however, the balance between the two immune effector arms depended on bacterial viability. Accordingly, live pneumococci triggered a Th1-biased response via monocyte production of IL-12p40, whereas heat-killed pneumococci triggered a Th17 response through TLR2 signaling. An increased understanding of human T helper responses is essential for the development of novel pneumococcal vaccines designed to elicit cell-mediated immunity.

Nasal immunization of mice with Lactobacillus casei expressing the pneumococcal surface protein C primes the immune system and decreases pneumococcal nasopharyngeal colonization in mice

Streptococcus pneumoniae colonizes the upper respiratory tract of healthy individuals, from where it can be transmitted to the community. Occasionally, bacteria invade sterile niches, causing diseases. The pneumococcal surface protein C (PspC) is a virulence factor that is important during colonization and the systemic phases of the diseases. Here, we have evaluated the effect of nasal or sublingual immunization of mice with Lactobacillus casei expressing PspC, as well as prime-boosting protocols using recombinant PspC, on nasopharyngeal pneumococcal colonization. None of the protocols tested was able to elicit significant levels of anti-PspC antibodies before challenge. However, a significant decrease in pneumococcal recovery from the nasopharynx was observed in animals immunized through the nasal route with L. casei-PspC. Immune responses evaluated after colonization challenge in this group of mice were characterized by an increase in mucosal anti-PspC immunoglobulin A (IgA) 5 days later, a time point in which the pneumococcal loads were already low. A negative correlation between the concentrations of anti-PspC IgA and pneumococcal recovery from the nasopharynx was observed, with animals with the lowest colonization levels having higher IgA concentrations. These results show that nasal immunization with L. casei-PspC primes the immune system of mice, prompting faster immune responses that result in a decrease in pneumococcal colonization.

The dectin-1/inflammasome pathway is responsible for the induction of protective T-helper 17 responses that discriminate between yeasts and hyphae of Candida albicans

In the mucosa, the immune pathways discriminating between colonizing and invasive Candida, thus inducing tolerance or inflammation, are poorly understood. Th17 responses induced by Candida albicans hyphae are central for the activation of mucosal antifungal immunity. An essential step for the discrimination between yeasts and hyphae and induction of Th17 responses is the activation of the inflammasome by C. albicans hyphae and the subsequent release of active IL-1β in macrophages. Inflammasome activation in macrophages results from differences in cell-wall architecture between yeasts and hyphae and is partly mediated by the dectin-1/Syk pathway. These results define the dectin-1/inflammasome pathway as the mechanism that enables the host immune system to mount a protective Th17 response and distinguish between colonization and tissue invasion by C. albicans.

Dual protective mechanisms of matrix metalloproteinases 2 and 9 in immune defense against Streptococcus pneumoniae

A localized and effective innate immune response to pathogenic bacterial invasion is central to host survival. Identification of the critical local innate mediators of lung defense against such pathogens is essential for a complete understanding of the mechanism(s) underlying effective host defense. In an acute model of Streptococcus pneumoniae lung infection, deficiency in matrix metalloproteinase (MMP)2 and MMP9 (Mmp2/9(-/-)) conferred a survival disadvantage relative to wild-type mice treated under the same conditions. S. pneumoniae-infected Mmp2/9(-/-) mice recruited more polymorphonuclear leukocytes to the lung but had higher bacterial burdens. Mmp2/9(-/-) mice showed significantly higher levels of IL-17A, IP-10, and RANTES in the lung. Although MMP2-dependent cleavage partially inactivated IL-17A, MMP9 was critical for effective bacterial phagocytosis and reactive oxygen species generation in polymorphonuclear neutrophils. These data demonstrate critical nonredundant and protective roles for MMP2 and MMP9 in the early host immune response against S. pneumoniae infection.

Serine protease PrtA from Streptococcus pneumoniae plays a role in the killing of S. pneumoniae by apolactoferrin

It is known that apolactoferrin, the iron-free form of human lactoferrin, can kill many species of bacteria, including Streptococcus pneumoniae. Lactoferricin, an N-terminal peptide of apolactoferrin, and fragments of it are even more bactericidal than apolactoferrin. In this study we found that apolactoferrin must be cleaved by a serine protease in order for it to kill pneumococci. The serine protease inhibitors were able to block killing by apolactoferrin but did not block killing by a lactoferrin-derived peptide. Thus, the killing of pneumococci by apolactoferrin appears to require a protease to release a lactoferricin-like peptide(s). Incubation of apolactoferrin with growing pneumococci resulted in a 12-kDa reduction in its molecular mass, of which about 7 to 8 kDa of the reduction was protease dependent. Capsular type 2 and 19F strains with mutations in the gene encoding the major cell wall-associated serine protease, prtA, lost much of their ability to degrade apolactoferrin and were relatively resistant to killing by apolactoferrin (P < 0.001). Recombinant PrtA was also able to cleave apolactoferrin, reducing its mass by about 8 kDa, and greatly enhance the killing activity of the solution containing the apolactoferrin and its cleavage products. Mass spectroscopy revealed that PrtA makes a major cut between amino acids 78 and 79 of human lactoferrin, removing the N-terminal end of the molecule (about 8.6 kDa). The simplest interpretation of these data is that the mechanism by which apolactoferrin kills Streptococcus pneumoniae requires the release of a lactoferricin-like peptide(s) and that it is this peptide(s), and not the intact apolactoferrin, which kills pneumococci.

Designed reduction of Streptococcus pneumoniae pathogenicity via synthetic changes in virulence factor codon-pair bias

In this study, we used a previously described method of controlling gene expression with computer-based gene design and de novo DNA synthesis to attenuate the virulence of Streptococcus pneumoniae. We produced 2 S. pneumoniae serotype 3 (SP3) strains in which the pneumolysin gene (ply) was recoded with underrepresented codon pairs while retaining its amino acid sequence and determined their ply expression and pneumolysin production in vitro and their virulence in a mouse pulmonary infection model. Expression of ply and production of pneumolysin of the recoded SP3 strains were decreased, and the recoded SP3 strains were less virulent in mice than the wild-type SP3 strain or a Δply SP3 strain. Further studies showed that the least virulent recoded strain induced a markedly reduced inflammatory response in the lungs compared with the wild-type or Δply strain. These findings suggest that reducing pneumococcal virulence gene expression by altering codon-pair bias could hold promise for rational design of live-attenuated pneumococcal vaccines.

Analysis of murine genetic predisposition to pneumococcal infection reveals a critical role of alveolar macrophages in maintaining the sterility of the lower respiratory tract

The study of pathogenic mechanisms of disease can be greatly facilitated by studying genetic differences in susceptibility to infection. In the present study, we compared the severity of pneumococcal infection in C57BL/6 (B6) and 129Sv mice. The results showed that 129Sv mice were remarkably more susceptible to pneumococcal infection than B6 mice. Bacterial clearance, proinflammatory mediators, leukocyte recruitment, and phagocyte activities were measured to examine potential immune factors associated with differences in susceptibility to pneumococcal infection. The greater susceptibility of 129Sv mice was associated only with inadequate alveolar macrophage bacterial killing, as indicated by significantly decreased initial bacterial clearance from the respiratory tract. Effective pneumococcal clearance was not dependent upon Toll-like receptor 2 (TLR2) expression, oxidative stress, or matrix metallopeptidase 12 (MMP-12) expression. Furthermore, phagocytosis analysis suggested that the deficiency found in 129Sv alveolar macrophages was not due to a lack of bacterial recognition but, rather, to reduced bacterial uptake. In conclusion, our findings indicate a crucial role of alveolar macrophage phagocytosis during innate defense against pneumococcal infection, which may explain the association of host genetic risk factors with predisposition to pneumococcal infection.

Natural antibodies against several pneumococcal virulence proteins in children during the pre-pneumococcal-vaccine era: the generation R study

The currently available pneumococcal vaccines do not protect against all serotypes of Streptococcus pneumoniae. A shift toward nonvaccine serotypes causing colonization and invasive disease has occurred, and studies on protein-based vaccines have been undertaken. We assessed the association between specific antibodies against pneumococcal virulence proteins and colonization and respiratory tract infections (RTIs). Additionally, we assessed the extent to which colonization induces a humoral immune response. Nasopharyngeal swabs collected from children at 1.5, 6, 14, and 24 months of age were cultured for pneumococcus. Serum samples were obtained at birth and at 6, 14, and 24 months (n = 57 children providing 177 serum samples). Data were collected prior to the pneumococcal vaccine era. IgG, IgA, and IgM levels against 17 pneumococcal protein vaccine candidates were measured using a bead-based flow cytometry technique (xMAP; Luminex Corporation). Information regarding RTIs was questionnaire derived. Levels of IgG against all proteins were high in cord blood, decreased in the first 6 months and increased again thereafter, in contrast to the course of IgA and IgM levels. Specific antibodies were induced upon colonization. Increased levels of IgG against BVH-3, NanA, and SP1003 at 6 months, NanA, PpmA, PsaA, SlrA, SP0189, and SP1003 at 14 months, and SlrA at 24 months were associated with a decreased number of RTIs in the third year of life but not with colonization. Maternal antipneumococcal antibodies did not protect against pneumococcal colonization and infection. Certain antibodies against pneumococcal virulence proteins, some of which are induced by colonization, are associated with a decreased number of RTIs in children. This should be taken into account in future pneumococcal vaccine studies.

Protecting the herd: the remarkable effectiveness of the bacterial meningitis polysaccharide-protein conjugate vaccines in altering transmission dynamics

Interrupting human-to-human transmission of the agents (Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae) of bacterial meningitis by new capsular polysaccharide-protein conjugate vaccines (PPCVs) has proven to be a remarkable (and unanticipated) contributor to vaccine effectiveness. Herd immunity accounts for ∼50% of the protection by meningococcal serogroup C PPCVs, pneumococcal PPCV7, and H. influenzae b PPCVs. Nasopharyngeal carriage can be reduced ≥75% for vaccine serotypes; the decrease in carriage is correlated with disease reduction in unvaccinated individuals, and the impact of herd immunity lasts for years. Based on these data, models for using herd immunity in vaccine-based prevention strategies are underway for control of meningitis in sub-Saharan Africa. Although the immunologic basis of herd immunity and impact on microbial biology need more study, protecting the unvaccinated by altering pathogen transmission dynamics is a powerful effect of PPCVs and increasingly important in vaccine introduction, implementation, and evaluation strategies.

CD8+ cells enhance resistance to pulmonary serotype 3 Streptococcus pneumoniae infection in mice

Despite the success of the pneumococcal conjugate vaccine, pneumococcal pneumonia remains a significant clinical problem, and there is still much to learn about natural resistance and cellular immunity to pneumococcus. We investigated the role of T lymphocytes in resistance to serotype (ST) 3 Streptococcus pneumoniae in an intranasal infection model in C57BL/6 (wild-type [Wt]) and CD8(+) (CD8(-/-))- and CD4(+) (MHC class II(-/-))-deficient mice. CD8(-/-) mice exhibited significantly more bacterial dissemination and lung inflammation and a significantly more lethal phenotype than Wt mice. However, there was no difference in the bacterial dissemination, lung inflammation, or survival of Wt and MHC class II(-/-) mice. Perforin (Pfn)(-/-) and IFN-γ(-/-) mice, which were used to dissect the role of CD8(+) T cells in our model, also exhibited a more lethal survival phenotype than Wt mice. Comparison of lung chemokine/cytokine levels by Luminex and cellular recruitment by FACS in Wt mice and knockout strains revealed that CD8(-/-) and IFN-γ(-/-) mice, which had the most lethal survival phenotype, had more CD4(+)IL-17(+) T (Th17) cells, IL-17, neutrophil chemoattractants, and lung neutrophils, and fewer regulatory T cells than Wt mice. CD4(+) T cell depletion improved the survival of ST-infected CD8(-/-) mice, and survival studies in Th17-deficient mice revealed that the Th17 response was dispensable for ST3 resistance in our model. Taken together, these findings demonstrate that CD8(+) cells are required, but CD4(+) T cells are dispensable for resistance to ST3 pneumonia in mice and suggest a previously unsuspected role for CD8(+) cells in modulating the inflammatory response to ST3.

Intranasal vaccination with chitosan-DNA nanoparticles expressing pneumococcal surface antigen a protects mice against nasopharyngeal colonization by Streptococcus pneumoniae

Streptococcus pneumoniae is a respiratory pathogen, and mucosal immune response plays a significant role in the defense against pneumococcal infections. Thus, intranasal vaccination may be an alternative approach to current immunization strategies, and effective delivery systems to mucosal organism are necessary. In this study, BALB/c mice were immunized intranasally with chitosan-DNA nanoparticles expressing pneumococcal surface antigen A (PsaA). Compared to levels in mice immunized with naked DNA or chitosan-pVAX1, anti-PsaA IgG antibody in serum and anti-IgA antibody in mucosal lavages were elevated significantly in mice immunized with chitosan-psaA. The balanced IgG1/IgG2a antibody ratio in serum, enhanced gamma interferon (IFN-γ) and IL-17A levels in spleen lymphocytes, and mucosal washes of mice immunized with chitosan-psaA suggested that cellular immune responses were induced. Furthermore, significantly fewer pneumococci were recovered from the nasopharynx of mice immunized with chitosan-psaA than for the control group following intranasal challenge with ATCC 6303 (serotype 3). These results demonstrated that mucosal immunization with chitosan-psaA may successfully generate mucosal and systemic immune responses and prevent pneumococcal nasopharyngeal colonization. Hence, a chitosan-DNA nanoparticle vaccine expressing pneumococcal major immunodominant antigens after intranasal administration could be developed to prevent pneumococcal infections.

Interleukin-1 receptor signaling is required to overcome the effects of pertussis toxin and for efficient infection- or vaccination-induced immunity against Bordetella pertussis

Interleukin-1 receptor-deficient (IL-1R(-/-)) mice are healthy despite being colonized by commensal microbes but are defective in defenses against specific pathogens, suggesting that IL-1R-mediated effects contribute to immune responses against specific pathogenic mechanisms. To better define the role of IL-1R in immunity to respiratory infections, we challenged IL-1R(-/-) mice with Bordetella pertussis and Bordetella parapertussis, the causative agents of whooping cough. Following inoculation with B. pertussis, but not B. parapertussis, IL-1R(-/-) mice showed elevated bacterial numbers and more extensive inflammatory pathology than wild-type mice. Acellular B. pertussis vaccines were not efficiently protective against B. pertussis in IL-1R(-/-) mice. B. pertussis-stimulated dendritic cells from IL-1R(-/-) mice produced higher levels of tumor necrosis factor alpha (TNF-α) and IL-6 than wild-type cells. Moreover, elevated levels of gamma interferon (IFN-γ) and TNF-α but lower levels of IL-10 were detected during B. pertussis infection in IL-1R(-/-) mice. Since B. parapertussis did not cause severe disease in IL-1R(-/-) mice, we hypothesized that the extreme requirement for IL-1R involves pertussis toxin (Ptx), which is expressed only by B. pertussis. An isogenic Ptx-deficient B. pertussis strain had only a modest phenotype in wild-type mice but was completely defective in causing lethal disease in IL-1R(-/-) mice, indicating that the particular virulence of B. pertussis in these mice requires Ptx. Ptx contributes to IL-1β induction by B. pertussis, which is involved in IL-10 induction through IL-1R signaling. IL-10 treatment reduced B. pertussis numbers in IL-1R(-/-) mice, suggesting that the lower IL-10 responses partially account for the uncontrolled inflammation and bacterial growth in these mice.

Protective role of interleukin-17 in murine NKT cell-driven acute experimental hepatitis

NKT cells are highly enriched within the liver. On activation NKT cells rapidly release large quantities of different cytokines which subsequently activate, recruit, or modulate cells important for the development of hepatic inflammation. Recently, it has been demonstrated that NKT cells can also produce interleukin-17 (IL-17), a proinflammatory cytokine that is also known to have diverse immunoregulatory effects. The role played by IL-17 in hepatic inflammation is unclear. Here we show that during α-galactosylceramide (αGalCer)-induced hepatitis in mice, a model of hepatitis driven by specific activation of the innate immune system via NKT cells within the liver, NK1.1+ and CD4+ iNKT cells rapidly produce IL-17 and are the main IL-17-producing cells within the liver. Administration of IL-17 neutralizing monoclonal antibodies before αGalCer injection significantly exacerbated hepatitis, in association with a significant increase in hepatic neutrophil and proinflammatory monocyte (ie, producing IL-12, tumor necrosis factor-α) recruitment, and increased hepatic mRNA and protein expression for the relevant neutrophil and monocyte chemokines CXCL5/LIX and CCL2/MCP-1, respectively. In contrast, administration of exogenous recombinant murine IL-17 before α-GalCer injection ameliorated hepatitis and inhibited the recruitment of inflammatory monocytes into the liver. Our results demonstrate that hepatic iNKT cells specifically activated with α-GalCer rapidly produce IL-17, and IL-17 produced after α-GalCer administration inhibits the development of hepatitis.

Th17 cells, Job's syndrome and HIV: opportunities for bacterial and fungal infections

PURPOSE OF REVIEW

Patients with hyper IgE syndrome (HIES) share with HIV patients a predisposition to infections, including candidiasis in autosomal dominant HIES (AD-HIES) and molluscum contagiosum and other viral infections in other disorders of elevated IgE with infectious predilections. This review highlights the underlying pathogenesis of these diseases and their relevance to HIV infection.

RECENT FINDINGS

Patients with mutations in STAT3, who lack Th17 cells, develop AD-HIES, whereas other disorders of elevated IgE may be caused by mutations in Tyk2 or DOCK8, the latter of which is associated with decreased expansion of CD8 more so than CD4 T cells. Recent studies on patients with recurrent mucocutaneous candidiasis have led to the discovery of mutations in CARD9 and DECTIN-1, genes key to the production of the Th17-driving cytokines IL-1beta, IL-6, and IL-23. Studies of the peripheral blood of HIV-positive patients have shown a decreased Th17:Th1 ratio, and Th17 cells were preferentially depleted from the gastrointestinal tract within weeks of simian immunodeficiency virus infection in rhesus macaques.

SUMMARY

The consequences of inadequate Th17 production in primary immunodeficiency syndromes illustrate the role of Th17 cells in controlling pathogens to which HIV-positive individuals are susceptible. Further understanding of the pathogenesis of opportunistic disease in HIV infection will probably require exploring the role of Th17 cells.

The Th1 immune response to Plasmodium falciparum circumsporozoite protein is boosted by adenovirus vectors 35 and 26 with a homologous insert

The most advanced malaria vaccine, RTS,S, is comprised of a portion of the Plasmodium falciparum circumsporozoite (CS) protein, fused to and admixed with the hepatitis B virus surface antigen, and an adjuvant [corrected].This vaccine confers short-term protection against malaria infection, with an efficacy of about 50%, and induces particularly B-cell and CD4(+) T-cell responses.In the present study, we tested the hypothesis that the Th1 immune response to CS protein,in particular the CD8(+) T-cell response, which is needed for strong and lasting malaria immunity, is boosted to sustainable levels by adenovirus vectors 35 and 26 with a homologous insert (Ad35.CS/Ad26.CS) [corrected]. In this study, we evaluated immune responses induced with vaccination regimens based on an adjuvant-containing, yeast-produced complete CS protein followed by two recombinant low-seroprevalence adenoviruses expressing P. falciparum CS antigen, Ad35.CS (subgroup B) and Ad26.CS (subgroup D). Our results show that (i) the yeast (Hansenula polymorpha)produced, adjuvanted full-length CS protein is highly potent in inducing high CS-specific humoral responses in mice but produces poor T-cell responses, (ii) the Ad35.CS vector boosts the gamma interferon-positive (IFN-γ(+)) CD8(+) T-cell response induced by the CS protein immunization and shifts the immune response toward the Th1 type, and (iii) a three-component heterologous vaccination comprised of a CS protein prime followed by boosts with Ad35.CS and Ad26.CS elicits an even more robust and sustainable IFN-γ(+) CD8(+) T-cell response than one- or two-component regimens. The Ad35.CS/Ad26.CS combination boosted particularly the IFN-γ(+) and tumor necrosis factor alpha-positive (TNF-α(+)) T cells, confirming the shift of the immune response from the Th2 type to the Th1 type. These results support the notion of first immunizations of infants with an adjuvanted CS protein vaccine, followed by a booster Ad35.CS/Ad26.CS vaccine at a later age, to induce lasting protection against malaria for which the Th1 response and immune memory is required.

Impaired T-cell receptor activation in IL-1 receptor-associated kinase-4-deficient patients

BACKGROUND

IL-1 receptor-associated kinase 4 (IRAK-4) is an effector of the Toll-like receptor and IL-1 receptor pathways that plays a critical role in innate immune responses. The role of IRAK-4 in adaptive immune functions in human subjects is incompletely understood.

OBJECTIVE

We sought to evaluate T-cell function in IRAK-4 deficient patients.

METHODS

We compared upregulation of CD25 and CD69 on T cells and production of IL-2, IL-6, and IFN-gamma after stimulation of PBMCs from 4 IRAK-4-deficient patients and healthy control subjects with anti-CD3 and anti-CD28.

RESULTS

Upregulation of CD25 and CD69 on T cells and production of IL-6 and IFN-gamma, but not IL-2, was significantly reduced in IRAK-4-deficient patients.

CONCLUSIONS

IRAK-4-deficient patients have defects in T-cell activation.

The efficacy of pneumococcal capsular polysaccharide-specific antibodies to serotype 3 Streptococcus pneumoniae requires macrophages

The efficacy of antibody immunity against Streptococcus pneumoniae stems from the ability of opsonic, serotype (ST)-specific antibodies to pneumococcal capsular polysaccharide (PPS) to facilitate killing of the homologous ST by host phagocytes. However, PPS-specific antibodies have been identified that are protective in mice, but do not promote opsonic killing in vitro, raising the question of how they mediate protection in vivo. To probe this question, we investigated the dependence of antibody efficacy against lethal systemic (intraperitoneal, i.p.) infection with Streptococcus pneumoniae serotype 3 (ST3) on macrophages and neutrophils for the following PPS3-specific monoclonal antibodies (MAbs) in survival experiments in mice using a non-opsonic human IgM (A7), a non-opsonic mouse IgG1 (1E2) and an opsonic mouse IgG1 (5F6). The survival of A7- and PPS3-specific and isotype control MAb-treated neutrophil-depleted and neutrophil-sufficient and macrophage-depleted and macrophage-sufficient mice were determined after i.p. challenge with ST3 strains 6303 and WU2. Neutrophils were dispensable for A7 and the mouse MAbs to mediate protection in this model, but macrophages were required for the efficacy of A7 and optimal mouse MAb-mediated protection. For A7-treated mice, macrophage-depleted mice had higher blood CFU, cytokines and peripheral neutrophil levels than macrophage-sufficient mice, and macrophage-sufficient mice had lower tissue bacterial burdens than control MAb-treated mice. These findings demonstrate that macrophages contribute to opsonic and non-opsonic PPS3-specific MAb-mediated protection against ST3 infection by enhancing bacterial clearance and suggest that neutrophils do not compensate for the absence of macrophages in the model used in this study.

Role of interleukin-17A in cell-mediated protection against Staphylococcus aureus infection in mice immunized with the fibrinogen-binding domain of clumping factor A

Clumping factor A (ClfA) is a fibrinogen-binding cell wall-attached protein and an important virulence factor of Staphylococcus aureus. Previous studies reported that an immunization with the fibrinogen-binding domain of ClfA (ClfA(40-559)) protected animals against S. aureus infection. It was reported that some cytokines are involved in the pathogenesis of staphylococcal diseases and in host defense against S. aureus infection. However, the role of cytokines in the protective effect of ClfA(40-559) as a vaccine has not been elucidated. In this study, we demonstrated that the spleen cells of ClfA(40-559)-immunized mice produced a large amount of interleukin-17A (IL-17A). The protective effect of immunization was exerted in wild-type mice but not in IL-17A-deficient mice. IL-17A mRNA expression was increased in the spleens and kidneys of immunized mice after infection. CXCL2 and CCL2 mRNA expression was increased in the spleens and kidneys, respectively. Consistent with upregulation of the mRNA expression, neutrophils infiltrated into the spleens extensively and macrophage infiltration was observed in the kidneys of immunized mice. These results suggest that immunization with ClfA(40-559) induces the IL-17A-producing cells and that IL-17-mediated cellular immunity is involved in the protective effect induced by immunization with ClfA(40-559) against S. aureus infection.