CD4+ T cells mediate antibody-independent acquired immunity to pneumococcal colonization

Mucosal immunization with the live attenuated vaccine SPY1 induces humoral and Th2-Th17-regulatory T cell cellular immunity and protects against pneumococcal infection

Mucosal immunization with attenuated vaccine can protect against pneumococcal invasion infection, but the mechanism was unknown. Our study found that mucosal delivery with the live attenuated SPY1 vaccine strain can confer T cell- and B cell-dependent protection against pneumococcal colonization and invasive infection; yet it is still unclear which cell subsets contribute to the protection, and their roles in pneumococcal colonization and invasion remain elusive. Adoptive transfer of anti-SPY1 antibody conferred protection to naive μMT mice, and immune T cells were indispensable to protection examined in nude mice. A critical role of interleukin 17A (IL-17A) in colonization was demonstrated in mice lacking IL-17A, and a vaccine-specific Th2 immune subset was necessary for systemic protection. Of note, we found that SPY1 could stimulate an immunoregulatory response and that SPY1-elicited regulatory T cells participated in protection against colonization and lethal infection. The data presented here aid our understanding of how live attenuated strains are able to function as effective vaccines and may contribute to a more comprehensive evaluation of live vaccines and other mucosal vaccines.

Role of non-conventional T lymphocytes in respiratory infections: the case of the pneumococcus

Non-conventional T lymphocytes constitute a special arm of the immune system and act as sentinels against pathogens at mucosal surfaces. These non-conventional T cells (including mucosal-associated invariant T [MAIT] cells, gamma delta [γδ] T cells, and natural killer T [NKT] cells) display several innate cell-like features and are rapidly activated by the recognition of conserved, stress-induced, self, and microbial ligands. Here, we review the role of non-conventional T cells during respiratory infections, with a particular focus on the encapsulated extracellular pathogen Streptococcus pneumoniae, the leading cause of bacterial pneumonia worldwide. We consider whether MAIT cells, γδ T cells, and NKT cells might offer opportunities for preventing and/or treating human pneumococcus infections.

Low antigen-specific CD4 T-cell immune responses despite normal absolute CD4 counts after long-term antiretroviral therapy an African cohort

BACKGROUND

CD4 counts guide antiretroviral therapy (ART) initiation and prophylaxis for opportunistic infections. It is unclear whether normal CD4 counts translate to normalized immune responses among ART-treated adults. We compared antigen-specific CD4 T-cell immune responses among ART-treated adults with CD4≥500cells/μl, optimal immune responders (O-IR), and their age-matched healthy HIV-negative counterparts.

METHODS

In a sample-based case-control study, cryopreserved peripheral blood mononuclear cells from 15 O-IR after 7 years of ART and 15 healthy controls, were analyzed for CD4+ T-cell proliferation using CFSE dye and cytokine production.

RESULTS

CD4 T-cell proliferation, upon stimulation with PPD and pneumococcal polysaccharide antigen, was lower among O-IR relative to HIV-negative controls; p=0.016 and p=0.016 respectively. CD4 T-cell production of IL-2 was lower among O-IR relative to HIV-negative control p=0.002. CD4 T-cell proliferation upon stimulation with SEB and CMV antigens was similar among O-IR and HIV-negative controls p=0.971 and p=0.480, respectively, and so was IL-4 and IFN γ production; p=0.528 and p=0.892, respectively.

CONCLUSION

Seven years of suppressive ART caused partial CD4 T-cell function recovery in an African HIV treatment cohort, despite restoration of CD4 T-cell counts to levels≥500cells/μl. The role innate immunity in the recovery of immune function during long-term ART should be investigated to guide decisions on continued prophylaxis against opportunistic infections.

Pathogen evolution and the immunological niche

Host immunity is a major driver of pathogen evolution and thus a major determinant of pathogen diversity. Explanations for pathogen diversity traditionally assume simple interactions between pathogens and the immune system, a view encapsulated by the susceptible-infected-recovered (SIR) model. However, there is growing evidence that the complexity of many host-pathogen interactions is dynamically important. This revised perspective requires broadening the definition of a pathogen's immunological phenotype, or what can be thought of as its immunological niche. After reviewing evidence that interactions between pathogens and host immunity drive much of pathogen evolution, I introduce the concept of a pathogen's immunological phenotype. Models that depart from the SIR paradigm demonstrate the utility of this perspective and show that it is particularly useful in understanding vaccine-induced evolution. This paper highlights questions in immunology, evolution, and ecology that must be answered to advance theories of pathogen diversity.

Pneumococcal vaccine and patients with pulmonary diseases

Chronic pulmonary diseases are chronic diseases that affect the airways and lung parenchyma. Examples of common chronic pulmonary diseases include asthma, bronchiectasis, chronic obstructive lung disease, lung fibrosis, sarcoidosis, pulmonary hypertension, and cor pulmonale. Pulmonary infection is considered a significant cause of mortality in patients with chronic pulmonary diseases. Streptococcus pneumoniae is the leading isolated bacteria from adult patients with community-acquired pneumonia, the most common pulmonary infection. Vaccination against S. pneumoniae can reduce the risk of mortality, especially from more serious infections in both immunocompetent and immunocompromised patients. Patients with chronic pulmonary diseases who take steroids or immunomodulating therapy (eg, methotrexate, anti-tumor necrosis factor inhibitors), or who have concurrent sickle cell disease or other hemoglobinopathies, primary immunodeficiency disorders, human immunodeficiency virus infection/acquired immunodeficiency syndrome, nephrotic syndrome, and hematologic or solid malignancies should be vaccinated with both 13-valent pneumococcal conjugate vaccine and the pneumococcal polysaccharide vaccine 23-valent.

Proteomics-identified Bvg-activated autotransporters protect against bordetella pertussis in a mouse model

Pertussis is a highly infectious respiratory disease of humans caused by the bacterium Bordetella pertussis. Despite high vaccination coverage, pertussis has re-emerged globally. Causes for the re-emergence of pertussis include limited duration of protection conferred by acellular pertussis vaccines (aP) and pathogen adaptation. Pathogen adaptations involve antigenic divergence with vaccine strains, the emergence of strains which show enhanced in vitro expression of a number of virulence-associated genes and of strains that do not express pertactin, an important aP component. Clearly, the identification of more effective B. pertussis vaccine antigens is of utmost importance. To identify novel antigens, we used proteomics to identify B. pertussis proteins regulated by the master virulence regulatory system BvgAS in vitro. Five candidates proteins were selected and it was confirmed that they were also expressed in the lungs of naïve mice seven days after infection. The five proteins were expressed in recombinant form, adjuvanted with alum and used to immunize mice as stand-alone antigens. Subsequent respiratory challenge showed that immunization with the autotransporters Vag8 and SphB1 significantly reduced bacterial load in the lungs. Whilst these antigens induced strong opsonizing antibody responses, we found that none of the tested alum-adjuvanted vaccines - including a three-component aP - reduced bacterial load in the nasopharynx, suggesting that alternative immunological responses may be required for efficient bacterial clearance from the nasopharynx.

Dynamics of lung defense in pneumonia: resistance, resilience, and remodeling

Pneumonia is initiated by microbes in the lung, but physiological processes integrating responses across diverse cell types and organ systems dictate the outcome of respiratory infection. Resistance, or actions of the host to eradicate living microbes, in the lungs involves a combination of innate and adaptive immune responses triggered by air-space infection. Resilience, or the ability of the host tissues to withstand the physiologically damaging effects of microbial and immune activities, is equally complex, precisely regulated, and determinative. Both immune resistance and tissue resilience are dynamic and change throughout the lifetime, but we are only beginning to understand such remodeling and how it contributes to the incidence of severe pneumonias, which diminishes as childhood progresses and then increases again among the elderly. Here, we review the concepts of resistance, resilience, and remodeling as they apply to pneumonia, highlighting recent advances and current significant knowledge gaps.

Directing traffic: IL-17 and IL-22 coordinate pulmonary immune defense

Respiratory infections and diseases are among the leading causes of death worldwide, and effective treatments probably require manipulating the inflammatory response to pathogenic microbes or allergens. Here, we review mechanisms controlling the production and functions of interleukin-17 (IL-17) and IL-22, cytokines that direct several aspects of lung immunity. Innate lymphocytes (γδ T cells, natural killer cells, innate lymphoid cells) are the major source of IL-17 and IL-22 during acute infections, while CD4(+) T-helper 17 (Th17) cells contribute to vaccine-induced immunity. The characterization of dendritic cell (DC) subsets has revealed their central roles in T-cell activation. CD11b(+) DCs stimulated with bacteria or fungi secrete IL-1β and IL-23, potent inducers of IL-17 and IL-22. On the other hand, recognition of viruses by plasmacytoid DCs inhibits IL-1β and IL-23 release, increasing susceptibility to bacterial superinfections. IL-17 and IL-22 primarily act on the lung epithelium, inducing antimicrobial proteins and neutrophil chemoattractants. Recent studies found that stimulation of macrophages and DCs with IL-17 also contributes to antibacterial immunity, while IL-22 promotes epithelial proliferation and repair following injury. Chronic diseases such as asthma and chronic obstructive pulmonary disease have been associated with IL-17 and IL-22 responses directed against innocuous antigens. Future studies will evaluate the therapeutic efficacy of targeting the IL-17/IL-22 pathway in pulmonary inflammation.

What does tympanostomy tube placement in children teach us about the association between atopic conditions and otitis media?

Otitis media is the most common infection second only to viral upper respiratory infection in the outpatient setting. Tympanostomy tube insertion (TTI) is the most common ambulatory surgical procedure in the USA. While many risk factors for otitis media have been identified, atopic conditions have been underrecognized as risk factors for recurrent and persistent otitis media. Given that asthma and other atopic conditions are the most common chronic conditions during childhood, it is worth examining the association between atopic conditions and risk of otitis media, which can provide insight into how atopic conditions influence the risk of microbial infections. This paper focuses its discussion on otitis media; however, it is important that the association between atopic conditions and risk of otitis media be interpreted in the context of the association of atopic conditions with increased risks of various microbial infections.

Activation of memory Th17 cells by domain 4 pneumolysin in human nasopharynx-associated lymphoid tissue and its association with pneumococcal carriage

Pneumococcal carriage is common in children that may account for the high incidence of disease in this age group. Recent studies in animals suggest an important role for CD4+ T cells, T helper type 17 (Th17) cells in particular, in pneumococcal clearance. Whether this Th17-mediated mechanism operates in humans and what pneumococcal components activate Th17 are unknown. We investigated the ability of domain 4 pneumolysin (D4Ply) to activate CD4+ T cells including Th17 in human nasopharynx-associated lymphoid tissue (NALT) and peripheral blood. We show that D4Ply elicited a prominent CD4+ T-cell proliferative response. More importantly, D4Ply elicited a significant memory Th17 response in NALT, and a moderate response in peripheral blood mononuclear cells (PBMCs). This D4Ply-elicited memory Th17 response was more marked in carriage- than in carriage+ children in both NALT and PBMCs. In contrast, no difference was shown in D4Ply-induced Th1 response between the two groups. We also show D4Ply activated human monocytes and murine macrophages that was in part dependent on Toll-like receptor 4 (TLR-4). Our results support a protective role of Th17 against pneumococcal carriage in human nasopharynx, and identify a novel property of D4Ply to activate Th17 in NALT that may offer an attractive vaccine candidate in intranasal immunization against pneumococcal infection.

Characterization of the inflammatory infiltrate in Streptococcus pneumoniae pneumonia in young and elderly patients

There is an increased susceptibility and mortality in the elderly due to pneumonia caused by Streptococcus pneumoniae. We aimed to assess the inflammatory cell composition with respect to age in pneumococcal pneumonia patients. Neutrophilic granulocytes and various lymphocyte and macrophage subpopulations were immunohistochemically quantified on lung tissue specimens of young (n = 5; mean age 8.4 years), middle-aged (n = 8; mean age 55.9 years) and elderly (n = 9; mean age 86.6 years) pneumonia patients with microbiologically proven S. pneumoniae pneumonia. We discovered a higher percentage of neutrophilic granulocytes in elderly as opposed to young patients (95 vs. 75%, p = 0.012). Conversely, young patients versus elderly patients had more alveolar macrophages (CD11c+: 20 vs. 9%, p = 0.029) and M1 macrophages (CD14+: 30 vs. 10%, p = 0.012 and HLA-DR+: 52 vs. 11%, p = 0.019). There was no significant difference concerning M2 macrophages and lymphocytes. Comparison of young patients with middle-aged patients showed similar significant results for alveolar macrophages (p = 0.019) and subsignificant results for M1 macrophages and neutrophilic granulocytes (p < 0.08). This is the first study characterizing the inflammatory infiltrate of pneumococcal pneumonia in situ. Our observations improve the understanding of the innate immune mechanisms of pneumococcal lung infection and point at the potential of therapies for restoring macrophage function and decreasing neutrophilic influx in order to help prevent or cure pneumonia.

Toll-like receptor 2-dependent protection against pneumococcal carriage by immunization with lipidated pneumococcal proteins

Infections with Streptococcus pneumoniae cause substantial morbidity and mortality, particularly in children in developing nations. Polysaccharide-conjugate vaccines provide protection against both invasive disease and colonization, but their use in developing countries is limited by restricted serotype coverage and expense of manufacture. Using proteomic screens, we recently identified several antigens that protected mice from pneumococcal colonization in a CD4(+) T cell- and interleukin-17A (IL-17A)-dependent manner. Since several of these proteins are lipidated, we hypothesized that their immunogenicity and impact on colonization are in part due to activation of Toll-like receptor 2 (TLR2), a receptor for lipoproteins. Here we show that lipidated versions of the antigens elicited significantly higher activation of both human embryonic kidney cells engineered to express TLR2 (HEK-TLR2) and wild-type (WT) murine macrophages than nonlipidated mutant antigens. Lipoprotein-stimulated secretion of proinflammatory cytokines was ∼10× to ∼100× lower in murine TLR2-deficient macrophages than in WT macrophages. Subcutaneous immunization of C57BL/6 mice with protein subunit vaccines containing one or two of these lipoproteins or protein fusion constructs bearing N-terminal lipid adducts elicited a robust IL-17A response and a significant reduction in colonization compared with immunization with alum alone. In contrast, immunization of Tlr2(-/-) mice elicited no detectable IL-17A response and no protection against pneumococcal colonization. These experiments suggest that the lipid moieties enhance the immunogenicity and protective efficacy of pneumococcal TH17 antigens through activation of TLR2. Thus, triggering TLR2 with an antigen-specific protein subunit formulation is a possible strategy for the development of a serotype-independent pneumococcal vaccine that would reduce pneumococcal carriage.

Immune response in nasopharynx, lung, and blood elicited by experimental nasal pneumococcal vaccines containing live or heat-killed lactobacilli as mucosal adjuvants

This work analyzes the humoral and cellular immune responses induced by live (LcV) and heat-killed (LcM) Lactobacillus casei associated with the pneumococcal antigen (P-Ag) at the nasopharynx level, considering nasal-associated lymphoid tissue (NALT) as the primary inductive site of the mucosal immune system, and lung and blood as effector sites. Levels of P-Ag IgA and IgG antibodies, main types of B and T cells, and cytokines in mucosal and systemic compartments were evaluated. The results showed that both LcM+P-Ag and LcV+P-Ag vaccines effectively induced IgA and IgG anti-P-Ag Abs in the upper and lower respiratory tract and plasma. These results correlated with increased IgA+ cells in NALT and lung that was induced by the experimental vaccines. Moreover, numbers of IgG+ cells increased in the blood. Profiles of inflammatory and regulatory cytokines were evaluated and their possible implications for the defense against pneumococci was assessed. Considering the overall results, the potential mechanisms of immune stimulation induced by LcM and LcV used as adjuvants are discussed. LcV and LcM showed similar effects on the immune system. Strain viability is not crucial for the stimulation of the antigen-specific immune response, and LcM is a convenient and effective mucosal adjuvant.

Impaired CD4+ and T-helper 17 cell memory response to Streptococcus pneumoniae is associated with elevated glucose and percent glycated hemoglobin A1c in Mexican Americans with type 2 diabetes mellitus

Individuals with type 2 diabetes are significantly more susceptible to pneumococcal infections than healthy individuals of the same age. Increased susceptibility is the result of impairments in both innate and adaptive immune systems. Given the central role of T-helper 17 (Th17) and T-regulatory (Treg) cells in pneumococcal infection and their altered phenotype in diabetes, this study was designed to analyze the Th17 and Treg cell responses to a whole heat-killed capsular type 2 strain of Streptococcus pneumoniae. Patients with diabetes demonstrated a lower frequency of total CD+T-cells, which showed a significant inverse association with elevated fasting blood glucose. Measurement of specific subsets indicated that those with diabetes had, low intracellular levels of interleukin (IL)-17, and lower pathogen-specific memory CD4+ and IL-17+ cell numbers. No significant difference was observed in the frequency of CD4+ and Th17 cells between those with and without diabetes. However, stratification of data by obesity indicated a significant increase in frequency of CD4+ and Th17 cells in obese individuals with diabetes compared with nonobese individual with diabetes. The memory CD+T-cell response was associated inversely with both fasting blood glucose and percent glycated hemoglobin A1c. This study demonstrated that those with type 2 diabetes have a diminished pathogen-specific memory CD4+ and Th17 response, and low percentages of CD+T-cells in response to S. pneumoniae stimulation.

A live-attenuated pneumococcal vaccine elicits CD4+ T-cell dependent class switching and provides serotype independent protection against acute otitis media

Acute otitis media (AOM) caused by Streptococcus pneumoniae remains one of the most common infectious diseases worldwide despite widespread vaccination. A major limitation of the currently licensed pneumococcal vaccines is the lack of efficacy against mucosal disease manifestations such as AOM, acute bacterial sinusitis and pneumonia. We sought to generate a novel class of live vaccines that (1) retain all major antigenic virulence proteins yet are fully attenuated and (2) protect against otitis media. A live vaccine candidate based on deletion of the signal recognition pathway component ftsY induced potent, serotype-independent protection against otitis media, sinusitis, pneumonia and invasive pneumococcal disease. Protection was maintained in animals coinfected with influenza virus, but was lost if mice were depleted of CD4(+) T cells at the time of vaccination. The live vaccine induced a strong serum IgG2a and IgG2b response that correlated with CD4(+) T-cell mediated class switching. Deletion of genes required for microbial adaptation to the host environment is a novel live attenuated vaccine strategy yielding the first experimental vaccine effective against pneumococcal otitis media.

Immunosenescence and pneumococcal disease: an imbalance in host-pathogen interactions

Respiratory infections are among the most important causes of morbidity and mortality from infectious diseases worldwide. The most common causative bacterium, Streptococcus pneumoniae, frequently colonises the upper respiratory tract, where it resides mostly asymptomatically. Occasionally, however, S pneumoniae can cause severe disease such as pneumonia. Local host immunity is essential to control colonising pathogens by preventing overgrowth, spread, and invasion. However, age-related immune deficits in elderly people, known as immunosenescence, might contribute to increased disease burden. We review present knowledge about immunosenescence in the respiratory tract against Gram-positive bacteria, particularly S pneumoniae. We discuss the possible underdetection of pneumococcal colonisation in elderly people, and suggest changes to present surveillance methods to improve understanding of the relation between colonisation and disease. We conclude that present knowledge about alteration of host-pathogen interactions by immunosenescence in the respiratory tract is insufficient, and that research is needed to enable improved measures for prevention.

Serotype-independent pneumococcal vaccines

Streptococcus pneumoniae remains an important cause of disease with high mortality and morbidity, especially in children and in the elderly. The widespread use of the polysaccharide conjugate vaccines in some countries has led to a significant decrease in invasive disease caused by vaccine serotypes, but an increase in disease caused by non-vaccine serotypes has impacted on the overall efficacy of these vaccines on pneumococcal disease. The obvious solution to overcome such shortcomings would be the development of new formulations that provide serotype-independent immunity. This review focuses on the most promising approaches, including protein antigens, whole cell pneumococcal vaccines, and recombinant bacteria expressing pneumococcal antigens. The protective capacity of these vaccine candidates against the different stages of pneumococcal infection, including colonization, mucosal disease, and invasive disease in animal models is reviewed. Some of the human trials that have already been performed or that are currently ongoing are presented. Finally, the feasibility and the possible shortcomings of these candidates in relation to an ideal vaccine against pneumococcal infections are discussed.

Immunomodulatory effects of vitamin D on innate and adaptive immune responses to Streptococcus pneumoniae

BACKGROUND

Streptococcus pneumoniae forms part of the normal nasopharyngeal flora but can also cause a broad spectrum of inflammatory diseases. Vitamin D has potent effects on human immunity, including induction of antimicrobial peptides and suppression of T-cell proliferation, but its ability to modulate the immune response to pneumococci is unknown.

METHODS

Monocyte-derived dendritic cells (DCs) were stimulated with pneumococcal peptidoglycan (PGN) in the presence or absence of vitamin D. Expression of maturation markers, cytokines, pattern recognition receptors, and antimicrobial peptides were measured with flow cytometry, enzyme-linked immunosorbent assay and quantitative polymerase chain reaction. Stimulated DCs were cocultured with autologous T-helper cells, and concentrations of T-helper (Th) 1-, Th17-, and regulatory T-cell-related cytokines were measured with enzyme-linked immunosorbent assay.

RESULTS

Vitamin D enhanced DC maturation and expression of the migration marker C-C chemokine receptor type 7 (CCR7) in PGN-stimulated cells. It also enhanced expression of key pattern recognition receptors (Toll-like receptor 2, Nucleotide-binding oligomerization domain-containing protein 2 [Nod2]) and induced a synergistic up-regulation of the inflammatory mediator IL-1β and the β-defensin Human Beta Defensin 3 (hBD-3). Furthermore, vitamin D skewed the DC-mediated T-helper response to PGN from an inflammatory Th1/Th17 phenotype toward a regulatory T-cell phenotype.

CONCLUSION

Vitamin D modulates key elements of innate immunity while dampening adaptive immune responses in DCs after pneumococcal challenge, which may have implications for prevention and treatment of pneumococcus-induced inflammation.

CD4 T cell memory and antibody responses directed against the pneumococcal histidine triad proteins PhtD and PhtE following nasopharyngeal colonization and immunization and their role in protection against pneumococcal colonization in mice

The present study was undertaken to understand the role of vaccine candidates PhtD and PhtE in pneumococcal nasopharyngeal (NP) colonization, their ability to induce CD4 T cell memory and antibody responses following primary NP colonization, and their contribution to protection against secondary pneumococcal colonization in mice. The study was also aimed at understanding the potential of immunization with PhtD and PhtE in eliciting qualitative CD4 T cell memory responses and protection against pneumococcal NP colonization in mice. PhtD and PhtE isogenic mutants in a TIGR4 background (TIGR4 ΔPhtD and TIGR4 ΔPhtE) were constructed and found to have a significantly reduced colonization density over time in the nasopharynges of mice compared to those of mice colonized with wild-type TIGR4. Mice with primary colonization by wild-type TIGR4, TIGR4 ΔPhtD, or TIGR4 ΔPhtE were protected against secondary colonization by wild-type TIGR4; nonetheless, the clearance of secondary colonization was slower in mice with primary colonization by either TIGR4 ΔPhtD or TIGR4 ΔPhtE than in mice with primary colonization by wild-type TIGR4. Colonization was found to be an immunizing event for PhtD and PhtE antigens (antibody response); however, we failed to detect any antigen (PhtD or PhtE)-specific CD4 T cell responses in any of the colonized groups of mice. Intranasal immunization with either PhtD or PhtE protein generated robust serum antibody and CD4 Th1-biased immune memory and conferred protection against pneumococcal colonization in mice. We conclude that PhtD and PhtE show promise as components in next-generation pneumococcal vaccine formulations.

Controlled human infection and rechallenge with Streptococcus pneumoniae reveals the protective efficacy of carriage in healthy adults

RATIONALE

The immunological and protective role of pneumococcal carriage in healthy adults is not known, but high rates of disease and death in the elderly are associated with low carriage prevalence.

OBJECTIVES

We employed an experimental human pneumococcal carriage model to investigate the immunizing effect of a single carriage episode.

METHODS

Seventy healthy adults were challenged, and of those with carriage, 10 were rechallenged intranasally with live 6B Streptococcus pneumoniae up to 11 months after clearance of the first carriage episode. Serum and nasal wash antibody responses were measured before and after each challenge.

MEASUREMENTS AND MAIN RESULTS

A total of 29 subjects were experimentally colonized. No subjects were colonized by experimental rechallenge, demonstrating the protective effect of initial carriage against subsequent infection. Carriage increased both mucosal and serum IgG levels to pneumococcal proteins and polysaccharide, resulting in a fourfold increase in opsonophagocytic activity. Importantly, passive transfer of postcarriage sera from colonized subjects conferred 70% protection against lethal challenge by a heterologous strain in a murine model of invasive pneumococcal pneumonia. These levels were significantly higher than the protection conferred by either precarriage sera (30%) or saline (10%).

CONCLUSIONS

Experimental human carriage resulted in mucosal and systemic immunological responses that conferred protection against recolonization and invasive pneumococcal disease. These data suggest that mucosal pneumococcal vaccination strategies may be important for vulnerable patient groups, particularly the elderly, who do not sustain carriage.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Acquisition of Streptococcus pneumoniae in pneumococcal conjugate vaccine-naïve South African children and their mothers

BACKGROUND

Pneumococcal nasopharyngeal colonization is a prerequisite to developing pneumococcal disease. We investigated the dynamics of pneumococcal colonization in perinatal HIV-unexposed and HIV-exposed children and their mothers and risk factors associated with new serotypes acquisition.

METHODS

Two hundred forty-three mother-child pairs (120 HIV-infected, 123 HIV-uninfected mothers) were studied at 4.4, 7.2, 9.4, 12.3 and 16.0 months of the child's age. Demographic data, nasopharyngeal swabs, as well as oropharyngeal swabs, from mothers were collected for pneumococcal conventional culture and serotyping by the Quellung method.

RESULTS

The rate of new serotype acquisition during the 16 months did not differ between HIV-exposed (49.1%) and HIV-unexposed (52.0%) children, or between HIV-infected (18.9%) and HIV-uninfected (19.5%) mothers. Serotypes included in the 7-valent pneumococcal conjugate vaccine (PCV7) were acquired more often by HIV-infected (10.0%) compared with HIV-uninfected mothers (6.4%; P = 0.03). On multivariate analysis, day-care attendance (adjusted odds ratio [AOR], = 1.80, P = 0.02) and maternal pneumococcal colonization (AOR = 1.54, P = 0.01) were positively associated with pneumococcal acquisition in the child, whereas breast-feeding had a protective effect on PCV7-serotype acquisition in HIV-uninfected children. New acquisition of PCV7 and PCV13 serotypes in the mother was positively associated with colonization in the child (AOR = 2.01, P = 0.006 and AOR = 2.04, P = 0.002, respectively).

CONCLUSIONS

There is an association of acquisition of PCV7 and PCV13 serotypes between young children and their mothers. The higher prevalence of PCV7 serotype in HIV-infected mothers suggests that they may be a reservoir for transmission of these serotypes, which could delay indirect effects of PCV in settings with a high HIV burden.

CD4+ T-cell responses among adults and young children in response to Streptococcus pneumoniae and Haemophilus influenzae vaccine candidate protein antigens

We characterized cytokine profiles of CD4(+) T-helper (h) cells in adults and young children to ascertain if responses occur to next-generation candidate vaccine antigens PspA, PcpA, PhtD, PhtE, Ply, LytB of Streptococcus pneumonia (Spn) and protein D and OMP26 of non-typeable Haemophilus influenzae (NTHi). Adults had vaccine antigen-specific Th1 and Th2 cells responsive to all antigens evaluated whereas young children had significant numbers of vaccine antigen-specific CD4(+) T cells producing IL-2, (p=0.004). Vaccine antigen-specific CD4(+) T-cell populations in adults were largely of effector (TEM) and/or central memory (TCM) phenotypes as defined by CD45RA(-)CCR7(+) or CD45RA(-)CCR7(-) respectively; however among young children antigen-specific IL-2 producing CD4(+) T cells demonstrated CD45RA(+) expression (non-memory cells). We conclude that adults have circulating memory CD4(+) T cells (CD45RA(-)) that can be stimulated by all the tested Spn and NTHi protein vaccine candidate antigens, whereas young children have a more limited response.

Protective anti-outer membrane protein immunity against Pasteurella pneumotropica infection of mice

The ability of recombinant outer membrane proteins of Pasteurella pneumotropica to vaccinate against the infections of mice was studied. The proteins examined were the homologues of the P4, P6, P26, and D15 proteins of Haemophilus influenzae. Intranasal vaccination with P4 and P6 produced protection against pneumonia. P6 vaccination, which was most studied, reduced the peak bacteria load in lungs by 50-fold and caused a rapid resolution of an infection that lasted for at least 5 days in unvaccinated animals. Protection could be partially transferred with CD4(+) T cells and pulmonary challenge with the P6 antigen induced interferon-γ and the Th17 cytokine IL-21. This is the first demonstration of the ability of a recombinant P6 to mediate protective immunity to a pathogen in its natural host and it is proposed that it would not only have utility for mouse breeding but also for investigating how to improve the efficacy of vaccination with homologous proteins for related species.

NADH oxidase functions as an adhesin in Streptococcus pneumoniae and elicits a protective immune response in mice

The initial event in disease caused by S. pneumoniae is adhesion of the bacterium to respiratory epithelial cells, mediated by surface expressed molecules including cell-wall proteins. NADH oxidase (NOX), which reduces free oxygen to water in the cytoplasm, was identified in a non-lectin enriched pneumococcal cell-wall fraction. Recombinant NOX (rNOX) was screened with sera obtained longitudinally from children and demonstrated age-dependent immunogenicity. NOX ablation in S. pneumoniae significantly reduced bacterial adhesion to A549 epithelial cells in vitro and their virulence in the intranasal or intraperitoneal challenge models in mice, compared to the parental strain. Supplementation of Δnox WU2 with the nox gene restored its virulence. Saturation of A549 target cells with rNOX or neutralization of cell-wall residing NOX using anti-rNOX antiserum decreased adhesion to A549 cells. rNOX-binding phages inhibited bacterial adhesion. Moreover, peptides derived from the human proteins contactin 4, chondroitin 4 sulfotraferase and laminin5, homologous to the insert peptides in the neutralizing phages, inhibited bacterial adhesion to the A549 cells. Furthermore, rNOX immunization of mice elicited a protective immune response to intranasal or intraperitoneal S. pneumoniae challenge, whereas pneumococcal virulence was neutralized by anti-rNOX antiserum prior to intraperitoneal challenge. Our results suggest that in addition to its enzymatic activity, NOX contributes to S. pneumoniae virulence as a putative adhesin and thus peptides derived from its target molecules may be considered for the treatment of pneumococcal infections. Finally, rNOX elicited a protective immune response in both aerobic and anaerobic environments, which renders NOX a candidate for future pneumococcal vaccine.

Bacterial respiratory pathogens in children with inherited immune and airway disorders: nasopharyngeal carriage and disease risk

Children with primary immunodeficiencies, sickle cell disease and cystic fibrosis are at risk to develop invasive bacterial infections caused by respiratory tract pathogens, in particular Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus. This review article evaluates the role of nasopharyngeal colonization by these pathogens in the high prevalence of respiratory and invasive infections in children with inherited disorders affecting the immune system or the respiratory tract. We conclude that respiratory and invasive diseases that occur in children with primary immunodeficiencies or sickle cell disease are probably a result of increased nasopharyngeal colonization rates compared with healthy children. However, when the inherited disorder is characterized by local airway abnormalities such as in cystic fibrosis, enhanced nasopharyngeal colonization does not seem to play a major role in invasive disease risk. As the evidence for the role of nasopharyngeal colonization in disease risk in these specific patient groups partly comes from experimental studies and animal models, longitudinal studies in children are needed. Detailed understanding of the effect of colonization on the development of respiratory and invasive infections in children with primary immunodeficiencies, sickle cell disease or cystic fibrosis provides a justification for the selective introduction of vaccination and prophylactic antibiotic treatment. Recommendations for the use of (preventive) therapeutic strategies in these patient groups taking into account disease-specific immunologic mechanisms underlying colonization and disease are described.

Clearance of Staphylococcus aureus nasal carriage is T cell dependent and mediated through interleukin-17A expression and neutrophil influx

The anterior nares of humans are the major reservoir for Staphylococcus aureus colonization. Approximately 20% of the healthy human population is persistently and 80% is intermittently colonized with S. aureus in the nasal cavity. Previous studies have shown a strong causal connection between S. aureus nasal carriage and increased risk of nosocomial infection, as well as increased carriage due to immune dysfunction. However, the immune responses that permit persistence or mediate clearance of S. aureus on the nasal mucosa are fundamentally undefined. In this study, we developed a carriage model in C57BL/6J mice and showed that clearance begins 14 days postinoculation. In contrast, SCID mice that have a deficient adaptive immune response are unable to eliminate S. aureus even after 28 days postinoculation. Furthermore, decolonization was found to be T cell mediated but B cell independent by evaluating carriage clearance in T-cell receptor β/δ (TCR-β/δ) knockout (KO) and IgH-μ KO mice, respectively. Upregulation of the cytokines interleukin 1β (IL-1β), KC (also termed CXC ligand 1 [CXCL1]), and IL-17A occurred following inoculation with intranasal S. aureus. IL-17A production was crucial for clearance, since IL-17A-deficient mice were unable to effectively eliminate S. aureus carriage. Subsequently, cell differential counts were evaluated from nasal lavage fluid obtained from wild-type and IL-17A-deficient colonized mice. These counts displayed IL-17A-dependent neutrophil migration. Antibody-mediated depletion of neutrophils in colonized mice caused reduced clearance compared to that in isotype-treated controls. Our data suggest that the Th17-associated immune response is required for nasal decolonization. This response is T cell dependent and mediated via IL-17A production and neutrophil influx. Th17-associated immune responses may be targeted for strategies to mitigate distal infections originating from persistent S. aureus carriage in humans.

Nanogel-based PspA intranasal vaccine prevents invasive disease and nasal colonization by Streptococcus pneumoniae

To establish a safer and more effective vaccine against pneumococcal respiratory infections, current knowledge regarding the antigens common among pneumococcal strains and improvements to the system for delivering these antigens across the mucosal barrier must be integrated. We developed a pneumococcal vaccine that combines the advantages of pneumococcal surface protein A (PspA) with a nontoxic intranasal vaccine delivery system based on a nanometer-sized hydrogel (nanogel) consisting of a cationic cholesteryl group-bearing pullulan (cCHP). The efficacy of the nanogel-based PspA nasal vaccine (cCHP-PspA) was tested in murine pneumococcal airway infection models. Intranasal vaccination with cCHP-PspA provided protective immunity against lethal challenge with Streptococcus pneumoniae Xen10, reduced colonization and invasion by bacteria in the upper and lower respiratory tracts, and induced systemic and nasal mucosal Th17 responses, high levels of PspA-specific serum immunoglobulin G (IgG), and nasal and bronchial IgA antibody responses. Moreover, there was no sign of PspA delivery by nanogel to either the olfactory bulbs or the central nervous system after intranasal administration. These results demonstrate the effectiveness and safety of the nanogel-based PspA nasal vaccine system as a universal mucosal vaccine against pneumococcal respiratory infection.

Defective pneumococcal-specific Th1 responses in HIV-infected adults precedes a loss of control of pneumococcal colonization

BACKGROUND

African adults infected with human immunodeficiency virus (HIV) have high rates of pneumococcal colonization and invasive disease. Here we have investigated the possibility that HIV disrupts the normal balance of pneumococcal-specific helper T cell (Th) 1/Th17 immunity to colonization, resulting in a more permissive nasopharyngeal niche.

METHODS

One hundred thirty-six HIV-infected and -uninfected Malawian adults were enrolled in the study. Changes in rates and composition of nasopharyngeal pneumococcal colonization were analyzed using microarray. The underlying pneumococcal-specific Th1/Th17 responses associated with altered pneumococcal colonization were investigated using flow cytometry.

RESULTS

We find that pneumococcal carriage is only modestly increased in asymptomatic HIV-infected Malawian adults but that colonization rates rise dramatically during symptomatic disease (HIV(neg) 13%, HIV(asy) 19%, and HIV(sym) 38%). These rates remain high in subjects established on antiretroviral therapy (ART): 33% (at 6-12 months) and 52% (at 18 months), with HIV-infected individuals carrying a broader range of invasive and noninvasive serotypes compared with HIV-negative controls. The frequency of multiple serotype carriage (>1 serotype HIV(neg) 26%, HIV(asy) 30%, HIV(sym) 31%, HIV(ART) 31%) is not affected. These changes in colonization are associated with generalized CD4 T-cell depletion, impaired antigen-specific proliferation, and a defect in pneumococcal-specific T-cell interferon-γ but not interleukin 17 production.

CONCLUSIONS

These data reveal the persistently poor control of pneumococcal colonization in HIV-infected adults following immune ART-mediated reconstitution, highlighting a potential reservoir for person-to-person spread and vaccine escape. Novel approaches to control colonization either through vaccination or through improvements in the quality of immune reconstitution are required.

The adjuvant double mutant Escherichia coli heat labile toxin enhances IL-17A production in human T cells specific for bacterial vaccine antigens

The strong adjuvant activity and low enterotoxicity of the novel mucosal adjuvant double mutant Escherichia coli heat labile toxin, LT(R192G/L211A) or dmLT, demonstrated in mice, makes this molecule a promising adjuvant candidate. However, little is known about the mechanisms responsible for the adjuvant effect of dmLT or whether dmLT also has an adjuvant function in humans.

We investigated the effect of dmLT on human T cell responses to different bacterial vaccine antigens: the mycobacterial purified protein derivative (PPD) antigen, tested in individuals previously vaccinated with Bacillus Calmette-Guérin, the LT binding subunit (LTB), evaluated in subjects immunised with oral inactivated whole cell vaccines against enterotoxigenic Escherichia coli, and Streptococcus pneumoniae whole cell vaccine antigens, tested in subjects naturally exposed to pneumococci. We found that dmLT enhanced the production of IL-17A by peripheral blood mononuclear cells in response to all antigens tested. dmLT had comparable effects on IL-17A responses to PPD as the single mutant LT(R192G) adjuvant, which has demonstrated clinical adjuvant activity in humans. Neutralisation of IL-1β and IL-23, but not IL-6, suppressed the IL-17A-enhancing effect of dmLT. Furthermore, CD4+ T cells produced higher levels of IL-17A when stimulated with monocytes pulsed with PPD and dmLT compared to PPD alone, supporting an important role of antigen presenting cells in enhancing IL-17A responses. dmLT also potentiated mitogen-induced IL-17A and IL-13 production. However, dmLT had variable influences on IFN-γ responses to the different stimuli tested.

Our demonstration of a potent ability of dmLT to enhance human Th17 type T cell responses to bacterial vaccine antigens encourages further evaluation of the adjuvant function of dmLT in humans.

MARCO is required for TLR2- and Nod2-mediated responses to Streptococcus pneumoniae and clearance of pneumococcal colonization in the murine nasopharynx

Streptococcus pneumoniae is a common human pathogen that accounts for >1 million deaths every year. Colonization of the nasopharynx by S. pneumoniae precedes pulmonary and other invasive diseases and, therefore, is a promising target for intervention. Because the receptors scavenger receptor A (SRA), macrophage receptor with collagenous structure (MARCO), and mannose receptor (MR) have been identified as nonopsonic receptors for S. pneumoniae in the lung, we used scavenger receptor knockout mice to study the roles of these receptors in the clearance of S. pneumoniae from the nasopharynx. MARCO(-/-), but not SRA(-/-) or MR(-/-), mice had significantly impaired clearance of S. pneumoniae from the nasopharynx. In addition to impairment in bacterial clearance, MARCO(-/-) mice had abrogated cytokine production and cellular recruitment to the nasopharynx following colonization. Furthermore, macrophages from MARCO(-/-) mice were deficient in cytokine and chemokine production, including type I IFNs, in response to S. pneumoniae. MARCO was required for maximal TLR2- and nucleotide-binding oligomerization domain-containing (Nod)2-dependent NF-κB activation and signaling that ultimately resulted in clearance. Thus, MARCO is an important component of anti-S. pneumoniae responses in the murine nasopharynx during colonization.

Distinct effects on diversifying selection by two mechanisms of immunity against Streptococcus pneumoniae

Antigenic variation to evade host immunity has long been assumed to be a driving force of diversifying selection in pathogens. Colonization by Streptococcus pneumoniae, which is central to the organism's transmission and therefore evolution, is limited by two arms of the immune system: antibody- and T cell- mediated immunity. In particular, the effector activity of CD4⁺ T_H17 cell mediated immunity has been shown to act in trans, clearing co-colonizing pneumococci that do not bear the relevant antigen. It is thus unclear whether T_H17 cell immunity allows benefit of antigenic variation and contributes to diversifying selection. Here we show that antigen-specific CD4⁺ T_H17 cell immunity almost equally reduces colonization by both an antigen-positive strain and a co-colonized, antigen-negative strain in a mouse model of pneumococcal carriage, thus potentially minimizing the advantage of escape from this type of immunity. Using a proteomic screening approach, we identified a list of candidate human CD4⁺ T_H17 cell antigens. Using this list and a previously published list of pneumococcal Antibody antigens, we bioinformatically assessed the signals of diversifying selection among the identified antigens compared to non-antigens. We found that Antibody antigen genes were significantly more likely to be under diversifying selection than the T_H17 cell antigen genes, which were indistinguishable from non-antigens. Within the Antibody antigens, epitopes recognized by human antibodies showed stronger evidence of diversifying selection. Taken together, the data suggest that T_H17 cell-mediated immunity, one form of T cell immunity that is important to limit carriage of antigen-positive pneumococcus, favors little diversifying selection in the targeted antigen. The results could provide new insight into pneumococcal vaccine design.

Streptococcus pneumoniae, or pneumococcus, is a leading cause of morbidity and mortality in young children and elderly persons worldwide. Current pneumococcus vaccines target a limited number of clinically important serotypes, while strains with serotypes not targeted by current vaccines are increasing in importance in both carriage and invasive disease. As a result, there has been a substantial interest to develop novel, cost-effective vaccines based on protein antigens from pneumococcus. To this end, it is critical to understand how the human immune system exerts selection pressures on the targeted antigens. Two immune mechanisms targeting pneumococcal protein antigens have been documented, mediated by antibody and T cells, respectively. In this study, we screened for pneumococcal antigens that are commonly recognized by human CD4⁺ T_H17 cells. Using a mouse model of pneumococcal colonization, we demonstrate that T_H17 cell-based immunity almost equally reduces colonization by both an antigen-positive strain and a co-colonizing, antigen-negative strain. Furthermore, we demonstrate that the DNA sequences of T_H17 cell antigens demonstrate no detectable signs of being under selective pressure, unlike pneumococcal antigens known to be strong antibody targets. Thus, one form of the T cell-mediated immunity that is important to limit carriage of antigen-positive pneumococcus favors little diversifying selection in the targeted antigen. These results suggest evolution of escape from T_H17 -based vaccines may be slower than from antibody-based vaccines.

The fundamental link between pneumococcal carriage and disease

Streptococcus pneumoniae (pneumococcus) is a major cause of worldwide mortality and morbidity, and to a large extent is vaccine-preventable. Nasopharyngeal carriage of pneumococcus precedes disease and is the source of pneumococcal spread between people. The use of vaccine effect on carriage as part of the vaccine licensure and post-vaccine introduction evaluation could facilitate and expand the licensure of new, life-saving pneumococcal vaccines and enable a comprehensive estimate of population effects after vaccine introduction. The authors provide a review of the evidence supporting pneumococcal carriage at the individual level as an immediate and necessary precursor to pneumococcal disease. Based on such a causal link between carriage and disease, the authors emphasize the role of information on pneumococcal carriage in vaccine trials and in public health decision-making.

Broad antibody and T cell reactivity induced by a pneumococcal whole-cell vaccine

Injecting mice with killed cells of non-capsulated strain RM200 adsorbed on Al(OH)3 (pneumococcal whole-cell vaccine; WCV) reduces nasopharyngeal colonization by capsular serotype 6B and prevents fatal aspiration pneumonia by serotype 3 or serotype 5 strains. To further examine the potential for omni-strain immunity, we here examined a panel of clinical isolates and a library of capsule-switch variants in the TIGR4 background. IgG binding to these bacteria in sera of rabbits injected with WCV or Al(OH)3 alone was assayed by ELISA without and with adsorption with cell-wall polysaccharide, a species-common antigen. The examined strains were 23 primary isolates including at least 10 different MLS types and 13 serotypes; 15 of these strains were invasive isolates, subsequently mouse-passed. Additionally, to investigate the effect of capsulation, TIGR4 strain constructs with the capsulation genes of 20 different serotypes were evaluated. In ELISA all strains showed a large difference in IgG binding due to the immunization, of which most of the antibody typically was not CWPS-adsorbed and presumably directed to exposed protein antigens. Increased binding of IgG in the WCV-immunized serum to the 20 isogenic capsule-switch strains was shown also by flow cytometry. Further, all these 20 strains elicited IL-17A in T cells of WCV-vaccinated mice, a cytokine known to accelerate pneumococcal clearance. Thus WCV induced both humoral and T(H)17 cell-mediated immunity against all tested strains.

Nonencapsulated Streptococcus pneumoniae resists extracellular human neutrophil elastase- and cathepsin G-mediated killing

Although the Streptococcus pneumoniae polysaccharide capsule is an important virulence factor, ~ 15% of carriage isolates are nonencapsulated. Nonencapsulated S. pneumoniae are a cause of mucosal infections. Recent studies have shown that neutrophils kill S. pneumoniae predominately through neutrophil proteases, such as elastase and cathepsin G. Another recent finding is that nonencapsulated pneumococci have greater resistance to resist cationic antimicrobial peptides that are important in mucosal immunity. We here show that nonencapsulated pneumococci have greater resistance to extracellular human neutrophil elastase- and cathepsin G-mediated killing than isogenic encapsulated pneumococci. Resistance to extracellular neutrophil protease-mediated killing is likely to be of greater relative importance on mucosal surfaces compared to other body sites.

The impact of the heptavalent pneumococcal conjugate vaccine on risk factors for Streptococcus pneumoniae carriage in children

BACKGROUND

The aim of the study was to investigate whether the 7-valent pneumococcal conjugate vaccine (PCV7) alters common risk factors of nasopharyngeal carriage by Streptococcus pneumoniae in children.

METHODS

From July 2005 through December 2010, we performed a cross-sectional study investigating risk factors associated with pneumococcal carriage in children. Parents of participating children completed questionnaires including whether or not the children received PCV7 vaccination.

RESULTS

Among 9705 children, 20.2% of them received at least 1 dose of the PCV7 vaccine. Multivariate logistic regression models identified older age, having 1 sibling in a family, history of acute otitis media and household exposure to smoking as independent risk factors for pneumococcal carriage in the unvaccinated group, but not associated with pneumococcal carriage in the vaccinated group. The number of siblings ≥2 in a family, history of upper respiratory tract infection and child-care attendance were strong factors associated with pneumococcal carriage in children, regardless of vaccination. In vaccinated group, breast-feeding was associated with increased nonvaccine type pneumococcal carriage, mainly in children with upper respiratory tract infection.

CONCLUSIONS

PCV7 decreased the association between pneumococcal carriage and older age, 1 sibling in a family, history of acute otitis media and household exposure to smoking, but increased the association between pneumococcal carriage and breast-feeding.

Interactions between Streptococcus pneumoniae and influenza virus: a mutually beneficial relationship?

Historically, most research on infectious diseases has focused on infections with single pathogens. However, infections with pathogens often occur in the context of pre-existing viral and bacterial infections. Clinically, this is of particular relevance for coinfections with Streptococcus pneumoniae and influenza virus, which together are an important cause of global morbidity and mortality. In recent years new evidence has emerged regarding the underlying mechanisms of influenza virus-induced susceptibility to secondary pneumococcal infections, in particular regarding the sustained suppression of innate recognition of S. pneumoniae. Conversely, it is also increasingly being recognized that there is not a unidirectional effect of the virus on S. pneumoniae, but that asymptomatic pneumococcal carriage may also affect subsequent influenza virus infection and the clinical outcome. Here, we will review both aspects of pneumococcal influenza virus infection, with a particular focus on the age-related differences in pneumococcal colonization rates and invasive pneumococcal disease.

Identification of protective pneumococcal T(H)17 antigens from the soluble fraction of a killed whole cell vaccine

Mucosal or parenteral immunization with a killed unencapsulated pneumococcal whole cell antigen (WCA) with an adjuvant protects mice from colonization by a T(H)17 CD4+ cell-mediated mechanism. Using preparative SDS gels, we separated the soluble proteins that compose the WCA in order to identify fractions that were immunogenic and protective. We screened these fractions for their ability to stimulate IL-17A secretion from splenocytes obtained from mice immunized with WCA and adjuvant. We identified 12 proteins within the stimulatory fractions by mass spectrometry; these proteins were then cloned, recombinantly expressed and purified using an Escherichia coli expression system. The ability of these proteins to induce IL-17A secretion was then evaluated by stimulation of mouse splenocytes. Of the four most stimulatory proteins, three were protective in a mouse pneumococcal serotype 6B colonization model. This work thus describes a method for identifying immunogenic proteins from the soluble fraction of pneumococcus and shows that several of the proteins identified protect mice from colonization when used as mucosal vaccines. We propose that, by providing protection against pneumococcal colonization, one or more of these proteins may serve as components of a multivalent pneumococcal vaccine.

Intranasal immunization with nontypeable Haemophilus influenzae outer membrane vesicles induces cross-protective immunity in mice

Haemophilus influenzae is a Gram-negative human-restricted bacterium that can act as a commensal and a pathogen of the respiratory tract. Especially nontypeable H. influenzae (NTHi) is a major threat to public health and is responsible for several infectious diseases in humans, such as pneumonia, sinusitis, and otitis media. Additionally, NTHi strains are highly associated with exacerbations in patients suffering from chronic obstructive pulmonary disease. Currently, there is no licensed vaccine against NTHi commercially available. Thus, this study investigated the utilization of outer membrane vesicles (OMVs) as a potential vaccine candidate against NTHi infections. We analyzed the immunogenic and protective properties of OMVs derived from various NTHi strains by means of nasopharyngeal immunization and colonization studies with BALB/c mice. The results presented herein demonstrate that an intranasal immunization with NTHi OMVs results in a robust and complex humoral and mucosal immune response. Immunoprecipitation revealed the most important immunogenic proteins, such as the heme utilization protein, protective surface antigen D15, heme binding protein A, and the outer membrane proteins P1, P2, P5 and P6. The induced immune response conferred not only protection against colonization with a homologous NTHi strain, which served as an OMV donor for the immunization mixtures, but also against a heterologous NTHi strain, whose OMVs were not part of the immunization mixtures. These findings indicate that OMVs derived from NTHi strains have a high potential to act as a vaccine against NTHi infections.

Tissue-expressed B7x affects the immune response to and outcome of lethal pulmonary infection

B7x (B7-H4 or B7S1), a member of the B7 family, inhibits in vitro T cell proliferation and cytokine production by binding to an unidentified receptor on activated T cells, but its in vivo function remains largely unclear. We show that B7x protein was expressed in epithelial cells of the lung, but not in lymphoid tissues. To investigate the role of B7x in the lung, we determined the susceptibility of B7x-deficient (B7x(-/-)) mice to a lethal pulmonary infection with Streptococcus pneumoniae. B7x(-/-), but not B7-H3-deficient, mice were significantly more resistant to S. pneumoniae pulmonary infection than their wild-type (Wt) counterparts. B7x(-/-) mice had significantly lower bacterial burdens and levels of inflammatory cytokines in lungs as early as 12 h postinfection. They also had milder immunopathology that was localized in alveolar spaces, whereas Wt mice had severe inflammation that was perivascular. Control of infection in B7x(-/-) mice was associated with a marked increase in activated CD4 and CD8 T cells and fewer neutrophils in lungs, whereas the susceptible Wt mice had the opposite cellular profile. In B7x(-/-)Rag1(-/-) mice that lack T cells, reduction in bacterial burden was no longer observed. Control of S. pneumoniae and the increased survival observed was specific to the lung, because systemically infected B7x(-/-) mice were not resistant to infection. These data indicate that lung-expressed B7x negatively regulates T cells, and that in its absence, in B7x(-/-) mice, an enhanced T cell response contributed to reduced lethality in a pulmonary infection model with S. pneumoniae.

Rates of acquisition and clearance of pneumococcal serotypes in the nasopharynges of children in Kilifi District, Kenya

Background. To understand and model the impact of pneumococcal conjugate vaccines at the population level, we need to know the transmission dynamics of individual pneumococcal serotypes. We estimated serotype-specific clearance and acquisition rates of nasopharyngeal colonization among Kenyan children.

Methods. Children aged 3–59 months who were identified as carriers in a cross-sectional survey were followed-up approximately 1, 2, 4, 8, 16, and 32 days later and monthly thereafter until culture of 2 consecutive swabs yielded an alternative serotype or no pneumococcus. Serotype-specific clearance rates were estimated by exponential regression of interval-censored carriage durations. Duration was estimated as the reciprocal of the clearance rate, and acquisition rates were estimated on the basis of prevalence and duration, assuming an equilibrium state.

Results. Of 2840 children sampled between October 2006 and December 2008, 1868 were carriers. The clearance rate was 0.032 episodes/day (95% confidence interval [CI], .030–.034), for a carriage duration of 31.3 days, and the rate varied by serotype (P < .0005). Carriage durations for the 28 serotypes with ≥10 carriers ranged from 6.7 to 50 days. Clearance rates increased with year of age, adjusted for serotype (hazard ratio, 1.21; 95% CI, 1.15–1.27). The acquisition rate was 0.061 episodes/day (95% CI, .055–.067), which did not vary with age. Serotype-specific acquisition rates varied from 0.0002 to 0.0022 episodes/day. Serotype-specific acquisition rates correlated with prevalence (r = 0.91; P < .00005) and with acquisition rates measured in a separate study involving 1404 newborns in Kilifi (r = 0.87; P < .00005).

Conclusions. The large sample size and short swabbing intervals provide a precise description of the prevalence, duration, and acquisition of carriage of 28 pneumococcal serotypes. In Kilifi, young children experience approximately 8 episodes of carriage per year. The declining prevalence with age is attributable to increasing clearance rates.

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.

Impaired function of antibodies to pneumococcal surface protein A but not to capsular polysaccharide in Mexican American adults with type 2 diabetes mellitus

The goal of the study was to determine baseline protective titers of antibodies to Streptococcus pneumoniae surface protein A (PspA) and capsular polysaccharide in individuals with and individuals without type 2 diabetes mellitus. A total of 561 individuals (131 individuals with diabetes and 491 without) were screened for antibodies to PspA using a standard enzyme-linked immunosorbent assay (ELISA). A subset of participants with antibodies to PspA were retested using a WHO ELISA to determine titers of antibodies to capsular polysaccharide (CPS) (serotypes 4, 6B, 9V, 14, 18C, 19A, 19F, and 23F). Functional activity of antibodies was measured by assessing their ability to enhance complement (C3) deposition on pneumococci and promote killing of opsonized pneumococci. Titers of antibodies to protein antigens (PspA) were significantly lower in individuals with diabetes than controls without diabetes (P = 0.01), and antibodies showed a significantly reduced complement deposition ability (P = 0.02). Both antibody titers and complement deposition were negatively associated with hyperglycemia. Conversely, titers of antibodies to capsular polysaccharides were either comparable between the two groups or were significantly higher in individuals with diabetes, as was observed for CPS 14 (P = 0.05). The plasma specimens from individuals with diabetes also demonstrated a higher opsonophagocytic index against CPS serotype 14. Although we demonstrate comparable protective titers of antibodies to CPS in individuals with and individuals without diabetes, those with diabetes had lower PspA titers and poor opsonic activity strongly associated with hyperglycemia. These results suggest a link between diabetes and impairment of antibody response.

Future perspective on host-pathogen interactions during bacterial biofilm formation within the nasopharynx

Nasopharyngeal colonization provides bacteria with a place of residence, a platform for person-to-person transmission and for many opportunistic pathogens it is a prerequisite event towards the development of invasive disease. Therefore, how host factors within the nasopharynx contribute to, inhibit or otherwise shape biofilm formation, the primary mode of existence for colonizing bacteria, and how biofilm bacteria subvert the acute inflammatory response that facilitates clearance, are important topics for future microbiological research. This review proposes the examination of host components as bridging molecules for bacterial interactions during biofilm formation, altered virulence determinant production and cell wall modification as a mechanism for immunoquiescence, and the role of host factors as signals and co-opted mechanisms for bacterial dissemination, together providing an opportunity for disease.

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.