Antibody-independent, interleukin-17A-mediated, cross-serotype immunity to pneumococci in mice immunized intranasally with the cell wall polysaccharide

Transcriptome profiling reveals Th17-like immune responses induced in zebrafish bath-vaccinated with a live attenuated Vibrio anguillarum

Background

A candidate vaccine, live attenuated Vibrio anguillarum developed in our laboratory could prevent vibriosis of fish resulted from V. anguillarum and V. alginolyticus. To elucidate the molecular mechanisms underlying the vaccine protection, we used microarray technology to compare the spleen transcriptomes of bath-vaccinated and unvaccinated zebrafish at 28 days post vaccination.

Principal Findings

A total of 2164 genes and transcripts were differentially expressed, accounting for 4.9% of all genes represented on the chip. In addition to iron metabolism related to the innate immunity and the signaling pathways, these differentially expressed genes also involved in the adaptive immunity, mainly including the genes associated with B and T cells activation, proliferation and expansion. Transcription profiles of Th17-related transcription factors, cytokines and cytokine receptors during 35 days post-vaccination implied that Th17 cells be activated in bath-vaccinated zebrafish.

Conclusion/Significance

The transcriptome profiling with microarray revealed the Th17-like immune response to bath-vaccination with the live attenuated V. anguillarum in zebrafish.

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.

Multiple antigen-presenting system (MAPS) to induce comprehensive B- and T-cell immunity

Vaccines are among the most effective approaches to prevent and control many infectious diseases. Because of safety and reproducibility concerns, whole-cell vaccines (WCVs), made from live or killed microorganisms and including hundreds of antigenic components, have been mostly replaced by acellular or subunit vaccines composed of well-defined, purified antigen components. The efficacy of acellular vaccines is inferior to that of WCVs, however, for two major reasons: limited antigen diversity and reduced immunogenicity, especially in a lack of activation of antigen-specific T-cell immunity, which plays an important role in protection against mucosal and intracellular pathogens. Here we present the multiple antigen-presenting system (MAPS), which enables the creation of a macromolecular complex that mimics the properties of WCVs by integrating various antigen components, including polysaccharides and proteins, in the same construct and that induces multipronged immune responses, including antibody, Th1, and Th17 responses. Using antigens from various pathogens (Streptococcus pneumoniae, Salmonella typhi, and Mycobacterium tuberculosis), we demonstrate the versatility of the MAPS system and its feasibility for the design of unique defined-structure subunit vaccines to confer comprehensive protection via multiple immune mechanisms. Moreover, MAPS can serve as a tool for structure-activity analysis of cellular immunogens.

T cell-mediated host immune defenses in the lung

Evidence has increasingly shown that the lungs are a major site of immune regulation. A robust and highly regulated immune response in the lung protects the host from pathogen infection, whereas an inefficient or deleterious response can lead to various pulmonary diseases. Many cell types, such as epithelial cells, dendritic cells, macrophages, neutrophils, eosinophils, and B and T lymphocytes, contribute to lung immunity. This review focuses on the recent advances in understanding how T lymphocytes mediate pulmonary host defenses against bacterial, viral, and fungal pathogens.

Interleukin-22 mediates early host defense against Rhizomucor pusilluscan pathogens

BACKGROUND

In recent years, the fungal infectious disease zygomycosis has increased in incidence worldwide, especially among the immunodeficient population. Despite the rates of zygomycosis-related death and deformation being very high, the mechanism(s) by which the fungal pathogens cause these severe manifestations remain unknown.

METHODS

Using the associated Rhizomucor variabilis species, which can selectively induce cutaneous zygomycosis in otherwise healthy individuals, we investigated the host mechanisms of infection-related responses, including cytokine and chemokine expression as well as contributions of particular T cell subsets. siRNA specifically targeting IL-22,IL-17 and IFN-γ were used to down-regulate expression of those molecules.

RESULTS

In mouse models of infection, IL-22 was implicated in development of Rhizomucor spp.-induced skin lesions. In cultured human peripheral blood monocytes, R. pusilluscan, which is often found in immunodeficient patients, induced the production of IL-22, while R. variabilis did not. Moreover, Rhizomucor spp.-induced secretion of Il-22 from CCR6(+)CCR4(+)CCR10(+) cells was down-regulated by knockdown of IL-22 related signaling receptors, RORC and ARH.

CONCLUSION

Our data strongly suggest that avoidance of IL-22 may be one mechanism by which mucor species produce morbidity and mortality in infected individuals.

T helper 17-associated cytokines are produced during antigen-specific inflammation in the mammary gland

Infectious mastitis cuts down milk production profitability and is a major animal welfare problem. Bacteria-induced inflammation in the mammary gland (MG) is driven by innate immunity, but adaptive immunity can modulate the innate response. Several studies have shown that it is possible to elicit inflammation in the MG by sensitization to an antigen subsequently infused into the lumen of the gland. The objective of our study was to characterize the inflammation triggered in the MG of cows sensitized to ovalbumin, by identifying the cytokines and chemokines likely to play a part in the reaction. Among immunized cows, responders mobilized locally high numbers of leukocytes. An overexpression of the genes encoding IL-17a, IL-17F, IL-21, IL-22 and INF-γ was found in milk cell RNA extracts in the early phase of the inflammatory response. At the protein level, IL-17A was detected in milk as soon as the first sampling time (8 h post-challenge), and both IL-17A and IFN-γ concentrations peaked at 12 to 24 h post-challenge. In mammary tissue from challenged quarters, overexpression of the genes encoding IL-17A, IL-17F, IL-21, IL-22, IL-26 and IFN-γ was observed. Neutrophil-attracting chemokines (CXCL3 and CXCL8) were found in milk, and overexpressed transcripts of chemokines attracting lymphocytes and other mononuclear leukocytes (CXCL10, CCL2, CCL5, CCL20) were detected in mammary tissue. Expression of IL-17A, as revealed by immunohistochemistry, was located in epithelial cells, in leukocytes in the connective tissue and in association with the epithelium, and in migrated alveolar leukocytes of challenged quarters. Altogether, these results show that antigen-specific inflammation in the MG was characterized by the production of IL-17 and IFN-γ. The orientation of the inflammatory response induced by the antigen-specific response has the potential to strongly impact the outcome of bacterial infections of the MG.

Th17 cell based vaccines in mucosal immunity

Vaccination is proven to be effective in controlling many infections including small pox, influenza and hepatitis, but strain-specific factors may limit vaccine efficacy. All of these vaccines work through the generation of neutralizing antibodies but for some pathogens there may be roles for serotype-independent immunity. Recently several groups using murine vaccine models have shown that induced T helper cell responses including Th17 responses have shown the potential for CD4+ T-cell dependent vaccine responses. Th17 mediated protective responses involve the recruitment of neutrophils, release of anti-microbial peptides and IL-17-driven Th1 immunity. These effector mechanisms provide immunity against a range of pathogens including the recently described antibiotic-resistant metallo-beta-lactamase 1 Klebsiella pneumoniae. Continued elucidation of the mechanism of Th17 responses and identification of effective adjuvants for inducing robust non pathogenic Th17 responses may lead to successful Th17 based vaccines. Here we summarize the recent advances in understanding the role of Th17 in vaccine induced immunity. We also discuss the current status and future challenges in Th17-based mucosal vaccine development.

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.

CD4(+) T-cell subsets and host defense in the lung

CD4(+) T-helper subsets are lineages of T cells that have effector function in the lung and control critical aspects of lung immunity. Depletion of these cells experimentally or by drugs or human immunodeficiency virus (HIV) infection in humans leads to the development of opportunistic infections as well as increased rates of bacteremia with certain bacterial pneumonias. Recently, it has been proposed that CD4(+) T-cell subsets may also be excellent targets for mucosal vaccination to prevent pulmonary infections in susceptible hosts. Here, we review recent findings that increase our understanding of T-cell subsets and their effector cytokines in the context of pulmonary 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.

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.

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.

The yin yang of bacterial polysaccharides: lessons learned from B. fragilis PSA

Over the past several years, there have been remarkable advances in our understanding of how commensal organisms shape host immunity. Although the full cast of immunogenic bacteria and their immunomodulatory molecules remains to be elucidated, lessons learned from the interactions between bacterial zwitterionic polysaccharides (ZPSs) and the host immune system represent an integral step toward better understanding how the intestinal microbiota effect immunologic changes. Somewhat paradoxically, ZPSs, which are found in numerous commensal organisms, are able to elicit both proinflammatory and immunoregulatory responses; both these outcomes involve fine-tuning the balance between T-helper 17 cells and interleukin-10-producing regulatory T cells. In this review, we discuss the immunomodulatory effects of the archetypal ZPS, Bacteroides fragilis PSA. In addition, we highlight some of the opportunities and challenges in applying these lessons in clinical settings.

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.

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.

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.

Correlates of vaccine protection from influenza and its complications

Despite use of influenza vaccines for more than 65 y, influenza and its complications are a major cause of morbidity and mortality worldwide. Most deaths during influenza virus infections are due to underlying co-morbidities or secondary bacterial pneumonia. The measures of immune response currently used for licensure of influenza vaccines are relevant mainly for protection from viral infection in healthy adults. Development of new or improved influenza vaccines will require a definition of novel, and specific correlates of protection. These correlates should associate immune responses with outcomes that are relevant to specific risk groups, such as asthma exacerbation, hospitalization or disruptions to care or daily activities. Assessment of vaccine effectiveness for both viral and bacterial vaccines should include measures of impact on secondary bacterial pneumonia.

Novel protein-based pneumococcal vaccines administered with the Th1-promoting adjuvant IC31 induce protective immunity against pneumococcal disease in neonatal mice

Streptococcus pneumoniae is responsible for many vaccine-preventable deaths, annually causing around 1 million deaths in children younger than 5 years of age. A new generation of pneumococcal vaccines based on conserved proteins is being developed. We evaluated the immunogenicities and protective efficacies of four pneumococcal protein vaccine candidates, PcsB, StkP, PsaA, and PspA, in a neonatal mouse model. Mice were immunized three times and challenged intranasally with virulent pneumococci. All four proteins were immunogenic in neonatal mice, and antibody (Ab) responses were significantly enhanced by the novel adjuvant IC31, which consists of an antibacterial peptide (KLKL5KLK) and a synthetic oligodeoxynucleotide, ODN1a, that signals through Toll-like receptor 9 (TLR9). Two single proteins, StkP and PspA, combined with IC31 significantly reduced pneumococcal bacteremia but had no effects on lung infection. Three proteins, PcsB, StkP, and PsaA, were evaluated with alum or IC31. IC31 enhanced Ab responses and avidity to all three proteins, whereas alum enhanced Ab responses and avidity to StkP and PsaA only. Mice receiving the trivalent protein formulation with IC31 had significantly reduced bacteremia and lung infection compared to unvaccinated mice, but the level of protection was dependent on the dose of IC31. When PspA was added to the trivalent protein formulation, the dose of IC31 needed to obtain protective immunity could be reduced. These results demonstrate that a novel pneumococcal protein-based vaccine is immunogenic at an early age of mice and emphasize the benefits of using a combination of conserved proteins and an effective adjuvant to elicit potent protective immunity against invasive pneumococcal disease.

Reduced memory CD4+ T-cell generation in the circulation of young children may contribute to the otitis-prone condition

BACKGROUND

An explanation for the immunologic dysfunction that causes children to be prone to repeated episodes of acute otitis media (AOM) has long been sought. Poor antibody response has been associated with the otitis-prone condition; however, there is no precise mechanistic explanation for this condition.

METHODS

Non-otitis-prone and otitis-prone children with AOM or nasopharyngeal (NP) colonization caused by either Streptococcus pneumoniae or Haemophilus influenzae were compared for pathogen-specific CD4(+) T-helper memory responses by stimulating peripheral blood mononuclear cells using 6 vaccine candidate S. pneumoniae and 3 H. influenzae protein antigens. Samples were analyzed by multi-parameter flow cytometry.

RESULTS

Significantly reduced percentages of functional CD45RA(Low) memory CD4(+) T cells producing specific cytokines (interferon γ, interleukin [IL]-2, IL-4 and IL-17a) were observed in otitis-prone children following AOM and NP colonization with either S. pneumoniae or H. influenzae. Immunoglobulin (Ig) G responses to the studied protein antigens were reduced, which suggests that antigen-specific B-cell function may be compromised as a result of poor T-cell help. Staphylococcal enterotoxin B stimulated similar cytokine patterns in memory CD4(+)T cells in both groups of children.

CONCLUSIONS

Otitis-prone children have suboptimal circulating functional T-helper memory and reduced IgG responses to S. pneumoniae or H. influenzae after colonization and after AOM; this immune dysfunction causes susceptibility to recurrent AOM infections.

Deteriorating pneumococcal-specific B-cell memory in minimally symptomatic African children with HIV infection

Invasive pneumococcal disease is a leading cause of human immunodeficiency virus (HIV)-associated mortality in sub-Saharan African children. Defective T-cell-mediated immunity partially explains this high disease burden, but there is an increased risk of invasive pneumococcal disease even in the context of a relatively preserved percentage of CD4 cells. We hypothesized that impaired B-cell immunity to this pathogen further amplifies the immune defect. We report a shift in the B-cell compartment toward an apoptosis-prone phenotype evident early in HIV disease progression. We show that, although healthy HIV-uninfected and minimally symptomatic HIV-infected children have similar numbers of isotype-switched memory B cells, numbers of pneumococcal protein antigen-specific memory B cells were lower in HIV-infected than in HIV-uninfected children. Our data implicate defective naturally acquired B-cell pneumococcal immunity in invasive pneumococcal disease causation in HIV-infected children and highlight the need to study the functionality and duration of immune memory to novel pneumococcal protein vaccine candidates in order to optimize their effectiveness in this population.

Impaired CD4 T cell memory response to Streptococcus pneumoniae precedes CD4 T cell depletion in HIV-infected Malawian adults

OBJECTIVE

Invasive pneumococcal disease (IPD) is a leading cause of morbidity and mortality in HIV-infected African adults. CD4 T cell depletion may partially explain this high disease burden but those with relatively preserved T cell numbers are still at increased risk of IPD. This study evaluated the extent of pneumococcal-specific T cell memory dysfunction in asymptomatic HIV infection early on in the evolution of the disease.

METHODS

Peripheral blood mononuclear cells were isolated from asymptomatic HIV-infected and HIV-uninfected Malawian adults and stained to characterize the underlying degree of CD4 T cell immune activation, senescence and regulation. Pneumococcal-specific T cell proliferation, IFN-γ, IL-17 production and CD154 expression was assessed using flow cytometry and ELISpot.

RESULTS

We find that in asymptomatic HIV-infected Malawian adults, there is considerable immune disruption with an increase in activated and senescent CD4+CD38+PD-1+ and CD4+CD25(high)Foxp3+ Treg cells. In the context of high pneumococcal exposure and therefore immune stimulation, show a failure in pneumococcal-specific memory T cell proliferation, skewing of T cell cytokine production with preservation of interleukin-17 but decreased interferon-gamma responses, and failure of activated T cells to express the co-stimulatory molecule CD154.

CONCLUSION

Asymptomatic HIV-infected Malawian adults show early signs of pneumococcal- specific immune dysregulation with a shift in the balance of CD4 memory, T helper 17 cells and Treg. Together these data offer a mechanistic understanding of how antigen-specific T cell dysfunction occurs prior to T cell depletion and may explain the early susceptibility to IPD in those with relatively preserved CD4 T cell numbers.

Alcohol abuse and Streptococcus pneumoniae infections: consideration of virulence factors and impaired immune responses

Alcohol is the most frequently abused substance in the world. Both acute and chronic alcohol consumption have diverse and well-documented effects on the human immune system, leading to increased susceptibility to infections like bacterial pneumonia. Streptococcus pneumoniae is the most common bacterial etiology of community-acquired pneumonia worldwide. The frequency and severity of pneumococcal infections in individuals with a history of alcohol abuse is much higher than the general population. Despite this obvious epidemiological relevance, very few experimental studies have focused on the interaction of pneumococci with the immune system of a host acutely or chronically exposed to alcohol. Understanding these host-pathogen interactions is imperative for designing effective prophylactic and therapeutic interventions for such populations. Recent advances in pneumococcal research have greatly improved our understanding of pneumococcal pathogenesis and virulence mechanisms. Additionally, a large body of data is available on the effect of alcohol on the physiology of the lungs and the innate and adaptive immune system of the host. The purpose of this review is to integrate the available knowledge in these diverse areas of for a better understanding of the how the compromised immune system derived from alcohol exposure responds to pneumococcal infections.

Antibody- and cell-mediated immune responses to a synthetic oligosaccharide conjugate vaccine after booster immunization

Memory formation to CRM-neoglycoconjugate, a synthetic branched tetrasaccharide of Streptococcus pneumoniae type 14 polysaccharide (Pn14PS) that is conjugated to a CRM197 protein, was investigated using mice models. Mice were first immunized with the CRM-neoglycoconjugate and then boosted with either the same neoglycoconjugate or a native Pn14PS in order to investigate the effect of booster immunization. Boosting with the CRM-neoglycoconjugate resulted in increased levels of interleukin 5 (IL-5) in the serum on Day 1, followed by the appearance of high levels of specific anti-Pn14PS IgG antibodies on Day 7. Boosting with native Pn14PS resulted in neither IL-5 induction nor the generation of anti-Pn14PS IgG antibodies. In vitro (re)stimulation of spleen cells after booster injection with the neoglycoconjugate revealed the presence of IL-4 and IL-5. This was not seen in spleen cells obtained from mice boosted with the polysaccharide. When stimulated with heat-inactivated bacteria, however, the polysaccharide-boosted mice did have higher levels of IFN-γ and lower levels of IL-17 than both the CRM-neoglycoconjugate-boosted mice and the mock-immunized mice. In conclusion, neoglycoconjugate boosting is responsible for the activation of memory cells and the establishment of sustained immunity. Not only is a booster with native polysaccharide ineffective in inducing opsonic antibodies, but it also interferes with several immunoregulatory mechanisms.

Lactic acid bacteria in the prevention of pneumococcal respiratory infection: future opportunities and challenges

Lactic acid bacteria (LAB) are technologically and commercially important and have various beneficial effects on human health. Several studies have demonstrated that certain LAB strains can exert their beneficial effect on the host through their immunomudulatory activity. Although most research concerning LAB-mediated enhanced immune protection is focused on gastrointestinal tract pathogens, recent studies have centered on whether these immunobiotics might sufficiently stimulate the common mucosal immune system to provide protection to other mucosal sites as well. In this sense, LAB have been used for the development of probiotic foods with the ability to stimulate respiratory immunity, which would increase resistance to infections, even in immunocompromised hosts. On the other hand, the advances in the molecular biology of LAB have enabled the development of recombinant strains expressing antigens from respiratory pathogens that have proved effective to induce protective immunity. In this review we examine the current scientific literature concerning the use of LAB strains to prevent respiratory infections. In particular, we have focused on the works that deal with the capacity of probiotic and recombinant LAB to improve the immune response against Streptococcus pneumoniae. Research from the last decade demonstrates that LAB represent a promising resource for the development of prevention strategies against respiratory infections that could be effective tools for medical application.

Vibrio cholerae O1 infection induces proinflammatory CD4+ T-cell responses in blood and intestinal mucosa of infected humans

Vibrio cholerae O1 is a noninvasive enteric pathogen and serves as a model for studies of mucosal immunity. Although symptomatic V. cholerae infection induces durable protection against subsequent disease, vaccination with oral killed whole-cell V. cholerae stimulates less long-lasting protection against cholera. In this study, we demonstrated that cholera induces an early proinflammatory cellular immune response that results in priming of Th1- and Th17-type cytokine responses to ex vivo antigenic stimulation and an increase in the ratio of Th1 to Th2 CD4(+) T-cell responses. Comparable priming of Th1 and Th17 responses, with an increased ratio of Th1 to Th2 CD4(+) T-cell responses, was not observed in subjects who received two doses of the oral cholera vaccine Dukoral (a whole-cell cholera toxin B subunit containing [WC-CTB] vaccine). These findings suggest that natural V. cholerae infection induces an early, proinflammatory cellular immune response, despite the apparent lack of clinical signs of inflammation. The failure of the WC-CTB vaccine to activate equivalent, CD4(+) T-cell responses is a potential explanation for the shorter duration of protection following immunization with this vaccine. Additional studies are needed to determine whether these early T-cell-mediated events predict the subsequent duration of immunologic memory.

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.

Tim-3 ligand galectin-9 reduces IL-17 level and accelerates Klebsiella pneumoniae infection

T cell immunoglobulin and mucin domain (Tim)-3 is expressed on activated CD4(+) and CD8(+) T cells. Identification of galectin-9 as a ligand for Tim-3 has now firmly established the Tim-3/galectin-9 pathway, which results in apoptosis of effector CD4(+) and CD8(+) T cells. Moreover, Th17 cells are a recently discovered CD4(+) effector T cell, which are important in antimicrobial immunity. Whether the Tim-3/galectin-9 pathway affects Th17 immunity has not been elucidated. Here, we demonstrated expression of Tim-3 on Th17 cells by flow cytometry. Th17-skewed cells were sensitive to galectin-9-induced apoptosis. In vitro administration of galectin-9 decreased stimulated Th17 cells and inhibited production of IL-17. Interestingly, Klebsiella pneumoniae (K. pneumoniae) infection led to enhanced IL-17 levels. Recombinant galectin-9 significantly decreased IL-17 in vivo, which resulted in reduced bacterial clearance and high mortality. These observations suggest that the Tim-3/galectin-9 pathway plays an important role in termination of Th17-immune responses, and could be a therapeutic target for inflammatory diseases.

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.

Review: T helper 17 cells: their role in glomerulonephritis

T helper (Th) cells are an integral part of the host's immune response to eliminate invading pathogens. However, autoimmune or 'autoinflammatory' diseases can develop if Th cell responses are not effectively regulated. Several subsets of Th cells exist, including the Th17 subset that produces interleukin-17A, important in experimental models of organ-specific autoimmune inflammation. Its discovery has explained paradoxical observations in model systems thought to be Th1 mediated but were exacerbated in the absence of interferon-gamma, the prototypic Th1 effector cytokine. Th17 cells express unique transcription factors and secrete a unique pattern of cytokines. Interleukin-17A induces pro-inflammatory cytokines and chemokines and mediates neutrophil recruitment. Th17 cells have a reciprocal relationship with T regulatory cells and can also mediate suppression of Th1 responses. Recent studies also suggest that Th17 cells are not terminally differentiated but can switch into Th1 cells. Th17 cells have themselves been recently shown to induce antigen-specific cell-mediated proliferative glomerulonephritis. There is increasing evidence implicating Th17 cells in anti-glomerular basement membrane disease, lupus nephritis and pauci-immune glomerulonephritis. This review will review the discovery of the Th17 subset, its properties, its relationship with other Th subsets and assess the current evidence implicating Th17 cells in glomerulonephritis.

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.

Regulation of Th17 cell differentiation by intestinal commensal bacteria

Interleukin (IL)-17-producing CD4 T cells ('Th17 cells') are most abundant at the intestinal mucosa, and play a critical role in the maintenance of mucosal barrier function. Recent studies indicate that accumulation of intestinal Th17 cells depends on stimulation by intestinal commensal bacteria – particularly by segmented filamentous bacterium. In this review, we summarise recent advances in our understanding of the mechanisms of intestinal Th17 synthesis in mice, and discuss their relevance to infectious and inflammatory diseases.

Educating CD4 T cells with vaccine adjuvants: lessons from lipopolysaccharide

Toll-like receptor (TLR) adjuvants are capable of driving T cell immunity. The TLR4 agonist LPS activates antigen-presenting cells through myeloid differentiation primary response gene 88 (MyD88) and TIR domain-containing adaptor inducing interferon-beta (TRIF)-dependent signaling pathways, initiating CD4 T helper cell clonal expansion and differentiation. Lipopolysaccharide (LPS) supports the development of diverse T helper (Th) lineages depending on the tissue microenvironment. For instance, peripheral immunization with LPS drives Th1 priming in lymphoid tissue and Th17 priming in the gut. This could be due to commensal bacteria inducing Th17-stabilizing cytokines within the intestinal lamina propria. Here, we detail how the response to LPS stimulates CD4 T cell priming in lymphoid tissue and the intestinal mucosa. How this knowledge might be exploited to target specific features of T cell immunity by vaccine adjuvants is also considered.

GMP-grade pneumococcal whole-cell vaccine injected subcutaneously protects mice from nasopharyngeal colonization and fatal aspiration-sepsis

Mucosal immunization with a killed whole-cell pneumococcal vaccine, given with enterotoxin-related adjuvants, has been shown to confer multi-serotype protection against colonization of the nasopharynx and middle ear in mice. However, because novel mucosal immunization strategies may be difficult to implement, here we evaluated subcutaneous injection. Strain RM200 was engineered to be capsule-negative, autolysin-negative, and to express a non-toxic mutant pneumolysoid. Liter-scale and 60-l Good Manufacturing Practice (GMP) cultures were grown in bovine-free soy-based medium, killed with chloroform or beta-propiolactone, and injected into C57Bl/6 mice without or with aluminum adjuvant. The adjuvant Al(OH)(3) strongly increased responses, particularly if pre-treated with phosphate. Protection was found in several tested model infections: nasal colonization with a serotype 6B strain and fatal aspiration-sepsis with strains of serotype 3 and 5. Protection against colonization was mechanistically dependent on the presence of CD4+ T cells at the time of challenge; in contrast, in the type 3 aspiration-sepsis model, CD4+ T cells were not required for protection at the time of challenge, suggesting that antibody alone was sufficient to protect against death in this model. Rabbits receiving sequential intramuscular injections in a pilot toxicity study displayed local reactogenicity at injection sites but no clinical signs. The rabbit antiserum thus produced was active in an in vitro phagocytic killing assay and passively protected mice in the type 3 aspiration-sepsis model. Approval is being sought for human trials of this vaccine.

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.

Th-17 cells in the lungs?

Naive CD4 cells are capable of integrating signals from antigen-activated cells of the innate immune system and differentiating into effector CD4 cells, also termed T helper (Th) cells. According to the traditional paradigm explaining adaptive CD4 cell responses, there are two subsets of Th cells: the Th-1 and Th-2 subset. Each of these subsets undergoes a distinct differentiation pathway (a pathway that is characterized by a unique profile of cytokine production and has specific immunoregulatory functions). However, recent studies in mouse models have forwarded evidence of a third subset of Th cells: the Th-17 subset. As indicated predominantly in studies on mice, the Th-17 subset is characterized by an ability to produce the neutrophil-mobilizing cytokine IL-17 in response to stimulation with the cytokine IL-23, an IL-12-related cytokine released from antigen-presenting cells. There is now a growing body of evidence from animal models that the Th-17 subset plays an important role in host defence in the lungs and other organs. Altered IL-17 levels have also been demonstrated in human patients with asthma, exacerbations of cystic fibrosis or following lung transplantation. There is now also evidence that the Th-17 subset is functionally distinct from the Th-2 subset but little is known of the functional inter-relationship between the Th-1 and Th-17 cell subsets; this is particularly true in human lungs. It has been proposed that the Th-17 subset plays a unique role by linking the arms of innate and adaptive immunity. Thus, an improved understanding of the human correlate to the Th-17 subset may reveal new targets for pharmacotherapy against lung disorders that are characterized by aberrant innate responses in host defense.

Prostaglandin E2-dependent IL-23 production in aged murine dendritic cells

CD4+ T cells of the Th17 subtype are over-represented in the aged immune system. Dendritic cells (DC) play a critical role in naïve CD4+ T cell differentiation. However, expression of cytokines by aged DC that promote differentiation or survival of Th17 cells has not been extensively investigated. Using bone marrow-derived DC from C57BL/6 mice of different ages we compared cytokine production after DC activation by Toll-like receptor agonists for TLR4 and/or TLR7/8. DC-derived TNF-α and IL-12p70 production and expression of DC co-stimulatory molecules did not vary significantly by age indicating that TLR expression, function and signal transduction were intact in aged DC. There were relatively minor age-related changes in TGF-β and IL-6 which promote Th17 differentiation, but IL-23, a Th17-suvival cytokine, increased more than 40-fold across the lifespan. DC-derived prostaglandin E2 (PGE2) also increased with age and the up-regulation of IL-23 expression by aged DC was blocked by indomethacin that prevents PGE2 production, and by antagonists of PGE2 receptors. Exogenous PGE2 added to DC cultures further enhanced IL-23 production from aged but not young DCs. These data indicate that age-related changes in DC PGE2 production are necessary, but not sufficient to induce DC IL-23 production. Such changes may play a role in the expansion of Th17 cells in the aged immune system.

Combination of pneumococcal surface protein A (PspA) with whole cell pertussis vaccine increases protection against pneumococcal challenge in mice

Streptococcus pneumoniae is the leading cause of respiratory acute infections around the world. In Latin America, approximately 20,000 children under 5 years of age die of pneumococcal diseases annually. Pneumococcal surface protein A (PspA) is among the best-characterized pneumococcal antigens that confer protection in animal models of pneumococcal infections and, as such, is a good alternative for the currently available conjugated vaccines. Efficient immune responses directed to PspA in animal models have already been described. Nevertheless, few low cost adjuvants for a subunit pneumococcal vaccine have been proposed to date. Here, we have tested the adjuvant properties of the whole cell Bordetella pertussis vaccine (wP) that is currently part of the DTP (diphtheria-tetanus-pertussis) vaccine administrated to children in several countries, as an adjuvant to PspA. Nasal immunization of BALB/c mice with a combination of PspA5 and wP or wP(low)--a new generation vaccine that contains low levels of B. pertussis LPS--conferred protection against a respiratory lethal challenge with S. pneumoniae. Both PspA5-wP and PspA5-wP(low) vaccines induced high levels of systemic and mucosal antibodies against PspA5, with similar profile, indicating no essential requirement for B. pertussis LPS in the adjuvant properties of wP. Accordingly, nasal immunization of C3H/HeJ mice with PspA5-wP conferred protection against the pneumococcal challenge, thus ruling out a role for TLR4 responses in the adjuvant activity and the protection mechanisms triggered by the vaccines. The high levels of anti-PspA5 antibodies correlated with increased cross-reactivity against PspAs from different clades and also reflected in cross-protection. In addition, passive immunization experiments indicated that antibodies played an important role in protection in this model. Finally, subcutaneous immunization with a combination of PspA5 with DTP(low) protected mice against challenge with two different pneumococcal strains, opening the possibility for the development of a combined infant vaccine composed of DTP and PspA.

Theories of otitis media pathogenesis, with a focus on Indigenous children

Otitis media is a common childhood illness associated with hearing loss, social disadvantage and medical costs. Prevalence and severity are high among Indigenous children. Respiratory bacterial and viral pathogens ascend the eustachian tube from the nasopharynx to the middle ear, causing inflammation, fluid accumulation, and bulging of the tympanic membrane, with or without pain. Among Australian Indigenous children, ear disease commences earlier in life, and involves multiple strains of bacterial pathogens at high density that persist longer. Persistent nasal discharge, overcrowded living conditions (particularly exposure to many children) and poor facilities for washing children perpetuate a vicious cycle of transmission and infection. Risk factors include environmental tobacco smoke, season, lack of breastfeeding, younger age and immature immune system, and possibly genetic factors. The innate immune system is a critical first response to infection, particularly as passive maternal antibodies decline and during the maturation of the infant adaptive immune response. The relative contributions of innate factors to protection from otitis media are currently not well understood. A diversity of antibodies that target strain-specific and conserved antigens are generated in response to natural exposure to otitis media pathogens (or to vaccines). Deficiencies in these antibodies may explain susceptibility to recurrent infections. Incremental contributions from all these elements are likely to be important in otitis media susceptibility versus protection. Effective medical and social strategies to prevent early age of onset are urgently needed.

Identification of the targets of cross-reactive antibodies induced by Streptococcus pneumoniae colonization

Much of the efficacy of current pneumococcal conjugate vaccines lies in their ability to decrease carriage of vaccine serotypes in the population. Novel and more-broadly acting vaccines would also need to target carriage in order to be as effective. We have previously shown that model murine carriage of Streptococcus pneumoniae can elicit antibody-dependent immunity and can protect against a virulent heterologous challenge strain. This study set out to identify S. pneumoniae surface antigens that may elicit cross-reactive antibodies following colonization. Western blot analysis using sera from colonized mice identified the previously characterized immunogens pneumococcal surface protein A (PspA), putative proteinase maturation protein A (PpmA), and pneumococcal surface adhesin A (PsaA) as such antigens. Using flow cytometry, PspA was found to be the major target of surface-bound cross-reactive IgG in sera from TIGR4 Delta cps-colonized mice, with a modest contribution from PpmA and none from PsaA. In human sera, however, only mutants lacking PpmA were shown to have reduced binding of surface IgG compared to wild-type strains, suggesting that prior exposure to S. pneumoniae in humans may induce PpmA antibodies. We also investigated if cross-reactive antibodies induced by these antigens may be cross-protective against carriage. Despite the immunogenicity of PspA, PpmA, and PsaA, mice were still protected following colonization with mutants lacking these antigens, suggesting they are not necessary for cross-protection induced by carriage. Our findings suggest that a whole-organism approach may be needed to broadly diminish carriage.

Protection against nasal colonization with Streptococcus pneumoniae by parenteral immunization with a DNA vaccine encoding PspA (Pneumococcal surface protein A)

Pneumococcal surface protein A (PspA) is an important candidate for a cost-effective vaccine with broad coverage against Streptococcus pneumoniae. We have previously shown that intramuscular immunization with PspA as a DNA vaccine induces an immune response characterized by the induction of a balanced IgG1/IgG2a antibody response in BALB/c mice, which was able to efficiently mediate complement deposition onto intact bacteria and to induce protection against an intraperitoneal challenge. We now confirm the results in C57BL/6 mice and further show that the response induced by the DNA vaccine expressing PspA is able to mediate protection against colonization of the nasopharyngeal mucosa even though immunization was given parenterally. Moreover, a positive correlation was observed between IgG1 and the numbers of CFU recovered, whereas an inverse correlation was observed between nasal CFU levels and IgG2a. A positive correlation was also found for IgG1/IgG2a antibody ratios with CFU recovered from the nasopharynx. Therefore, reduction of nasal colonization was strongly associated with increased levels of serum IgG2a complement fixing antibody and low levels of IgG1 antibody which has much less complement fixing activity. Passive transfer of serum from animals immunized with the DNA vaccine expressing PspA was also able to reduce the fraction of mice with high density of colonization of the nasopharynx. Secretion of IFN-gamma, but not IL-17, was observed in splenocytes from mice immunized with the DNA vaccine.

Helper T cell epitope-mapping reveals MHC-peptide binding affinities that correlate with T helper cell responses to pneumococcal surface protein A

Understanding the requirements for protection against pneumococcal carriage and pneumonia will greatly benefit efforts in controlling these diseases. Several proteins and polysaccharide capsule have recently been implicated in the virulence of and protective immunity against Streptococcus pneumonia. Pneumococcal surface protein A (PspA) is highly conserved among S. pneumonia strains, inhibits complement activation, binds lactoferrin, elicits protective systemic immunity against pneumococcal infection, and is necessary for full pneumococcal virulence. Identification of PspA peptides that optimally bind human leukocyte antigen (HLA) would greatly contribute to global vaccine efforts, but this is hindered by the multitude of HLA polymorphisms. Here, we have used an experimental data set of 54 PspA peptides and in silico methods to predict peptide binding to HLA and murine major histocompatibility complex (MHC) class II. We also characterized spleen- and cervical lymph node (CLN)-derived helper T lymphocyte (HTL) cytokine responses to these peptides after S. pneumonia strain EF3030-challenge in mice. Individual, yet overlapping peptides, 15 amino acids in length revealed residues 199 to 246 of PspA (PspA_199–246) consistently caused the greatest IFN-γ, IL-2, IL-5 and proliferation as well as moderate IL-10 and IL-4 responses by ex vivo stimulated splenic and CLN CD4⁺ T cells isolated from S. pneumonia strain EF3030-challeged F₁ (B6×BALB/c) mice. IEDB, RANKPEP, SVMHC, MHCPred, and SYFPEITHI in silico analysis tools revealed peptides in PspA_199–246 also interact with a broad range of HLA-DR, -DQ, and -DP allelles. These data suggest that predicted MHC class II-peptide binding affinities do not always correlate with T helper (Th) cytokine or proliferative responses to PspA peptides, but when used together with in vivo validation can be a useful tool to choose candidate pneumococcal HTL epitopes.

Translational mini-review series on Th17 cells: development of mouse and human T helper 17 cells

There has been a considerable amount of interest in the immunological community about new phenotypic subsets of CD4(+) T cells, particularly cells that produce the cytokine interleukin (IL)-17 [named T helper type 17 (Th17) cells]. While the initial discovery of Th17 cells and the pathways that controlled their development was in the mouse, recent attention has shifted to the existence of these cells and the relevant upstream cytokine signals in humans. While it is clear that CD4(+) T cells producing IL-17 exist in vivo, their relevance to disease pathogenesis is only just being understood. In this paper, we review the data regarding the generation of human Th17 cells in vitro and the evidence that this effector population is important in human disease states.

Th17 cytokines and vaccine-induced immunity

T helper type 17 (Th17) cells are a distinct lineage of T cells that produce the effector molecules IL-17, IL-17F, IL-21, and IL-22. Although the role of Th17 cells in primary immune responses against infections is well documented, there is growing evidence that the Th17 lineage maybe critical for vaccine-induced memory immune responses against infectious diseases. Here, we summarize recent progress in our understanding of the role of IL-17 in vaccine-induced immunity.

Th17 cells are the dominant T cell subtype primed by Shigella flexneri mediating protective immunity

The T cell response to Shigella, the causative agent of bacillary dysentery, remains poorly understood. Using a murine model of infection, we report that Shigella flexneri primes predominately IL-17A- and IL-22-producing Th17 cells. Shigella-specific Th1 cells are only significantly induced on secondary infection, whereas specific Th2 and CD8(+) T cells are undetectable. Apart from Th17 cells that are primed in a MHC class II- and IL-6-dependent, but IL12/23p40-independent manner, we identified gammadelta T cells as an additional but minor source of IL-17A. Priming of IL-17A(+) gammadelta T cells is dependent on IL12/23p40, but independent of MHC-class II and IL-6. Th17 cells have emerged as important players in inflammatory, autoimmune, and infectious diseases. Among the yet unresolved questions is their role in long-term immunity to pathogens. In this study, we show that the elicited S. flexneri-specific Th17 pool gives rise to an enhanced recall response up to 12 mo after priming, suggesting the presence of a long-term memory state. The clearance of primary infection is impaired in the absence of T cells, but independently of IL-17A. However, after reinfection, IL-17A produced by S. flexneri-specific Th17 cells becomes important to ultimately restrict bacterial growth. These findings bring new insights into the adaptive immune response to Shigella infection and highlight the importance of pathogen-specific Th17 cell immunity for secondary immune protection.

Antibody and cell-mediated immunity to Streptococcus pneumoniae: implications for vaccine development

It has long been assumed that children develop natural immunity to pneumococci via the acquisition of anticapsular antibodies, which confers serotype-specific immunity to the organism. This view has been further reinforced by the recent success of capsular polysaccharide conjugate vaccines in children in reducing colonization and disease caused by vaccine-type strains. Less clear, however, is whether this mechanism is responsible for the age-related gradual increased resistance to pneumococcal carriage and disease. Recent epidemiologic and experimental evidence point to the possibility that another mechanism may be involved. Here, an alternative possibility is presented, whereby it is proposed that acquired immunity to this common human pathogen is derived not only from natural acquisition of antibodies (capsular and noncapsular) that provides protection against invasive disease but also from the development of pneumococcus-specific CD4+ T(H)17 cells that reduces the duration of carriage and may also impact mucosal disease. This review focuses on the experimental and clinical evidence in support of this hypothesis. The implications for future vaccine development against Streptococcus pneumoniae are also discussed.

Immune responses to gut microbiota-commensals and pathogens

The mammalian alimentary tract harbors hundreds of species of commensal microorganisms that intimately interact with the host immune system. Within the gut, the immune system actively reacts with potentially pathogenic microbes, while simultaneously remaining ignorant towards the vast majority of non-pathogenic microbiota. The disruption of this delicate balance results in inflammatory bowel diseases. In this review, we describe the recent advances in our understanding of how host-microbiota interactions shape the immune system and how they affect the responses against pathogenic bacteria.

Splenic autotransplantation restores IL-17 production and antibody response to Streptococcus pneumoniae in splenectomized mice

The high incidence of overwhelming postsplenectomy infection caused by Streptococcus pneumoniae can be reduced by splenic autotransplantation. In this study the effect of splenectomy and splenic autotransplantation on the immune response to S. pneumoniae infection was investigated. Balb/c mice were divided into three groups: splenectomized (SP), splenectomized and autotransplanted (AT), and sham operated control (CT). Five days post-infection the serum antibody levels were measured and the number of S. pneumoniae CFU, neutrophil accumulation and IL-17 production in the liver and lungs were investigated. SP mice showed greater number of bacteria in both organs and lower serum levels of S. pneumoniae-specific IgM, IgG1 and IgG2a antibodies. IL-17 production and neutrophil recruitment to the liver and lungs were lower in SP mice, in comparison with both the CT and the AT groups. Levels of S. pneumoniae-specific IgM, CFU counts, neutrophil accumulation and IL-17 production did not differ significantly between the CT and AT groups. These results suggest that splenic autotransplantation restores the capacity of splenectomized mice to fight S. pneumoniae infection.