Characterisation of regulatory T cells in nasal associated lymphoid tissue in children: relationships with pneumococcal colonization

Mucosal immunity in upper and lower respiratory tract to MERS-CoV

Introduction

Middle East respiratory syndrome coronavirus (MERS-CoV) has emerged as a deadly pathogen with a mortality rate of up to 36.2%. MERS-CoV can cause severe respiratory tract disease and multiorgan failure. Therefore, therapeutic vaccines are urgently needed. This intensive review explores the human immune responses and their immunological mechanisms during MERS-CoV infection in the mucosa of the upper and lower respiratory tracts (URT and LRT, respectively).

Objective

The aim of this study is to provide a valuable, informative, and critical summary of the protective immune mechanisms against MERS-CoV infection in the URT/LRT for the purpose of preventing and controlling MERS-CoV disease and designing effective therapeutic vaccines.

Methods

In this review, we focus on the immune potential of the respiratory tract following MERS-CoV infection. We searched PubMed, Embase, Web of Science, Cochrane, Scopus, and Google Scholar using the following terms: "MERS-CoV", "B cells", "T cells", "cytokines", "chemokines", "cytotoxic", and "upper and lower respiratory tracts".

Results

We found and included 152 studies in this review. We report that the cellular innate immune response, including macrophages, dendritic cells, and natural killer cells, produces antiviral substances such as interferons and interleukins to prevent the virus from spreading. In the adaptive and humoral immune responses, CD4+ helper T cells, CD8+ cytotoxic T cells, B cells, and plasma cells protect against MERS-CoV infection in URT and LRT.

Conclusion

The human nasopharynx-associated lymphoid tissue (NALT) and bronchus-associated lymphoid tissue (BALT) could successfully limit the spread of several respiratory pathogens. However, in the case of MERS-CoV infection, limited research has been conducted in humans with regard to immunopathogenesis and mucosal immune responses due to the lack of relevant tissues. A better understanding of the immune mechanisms of the URT and LRT is vital for the design and development of effective MERS-CoV vaccines.

The role of adenoid immune phenotype in polysensitized children with allergic rhinitis and adenoid hypertrophy

BACKGROUND

There is increasing interest in elucidating the relationship between adenoid hypertrophy (AH) and allergic rhinitis (AR). However, the impact of aeroallergen sensitization patterns on children with AH and AR remains unclear.

METHODS

Patients aged 2-8 years (recruited from January 2019 to December 2022) with nasal symptoms were assessed for allergies, adenoid size, and respiratory viral infection history. The serum total immunoglobulin E (IgE) and specific IgE levels were measured, and flexible nasal endoscopy was performed. The relationship between AH, aeroallergen sensitization patterns, and lymphocyte subpopulations in adenoid samples was analyzed using flow cytometry.

RESULTS

In total, 5281 children were enrolled (56.5% with AR; and 48.6% with AH). AH was more prevalent in children with AR. Compared to nonsensitized individuals, those polysensitized to molds had a higher prevalence of AH (adjusted OR 1.61, 95% CI 1.32-1.96) and a greater occurrence of two or more respiratory viral infections, particularly in adenoidectomy patients. The percentages and corrected absolute counts of regulatory T (Treg) cells, activated Tregs, class-switched memory B cells (CSMBs), natural killer (NK) T cells, and NK cell subpopulations were reduced in the adenoid tissues of children with both AH and AR (AH-AR) compared to AH-nAR children. Polysensitization in AH-AR children correlated with lower CSMB percentages.

CONCLUSION

Polysensitivity to molds is associated with an increased risk of AH in children with AR. Fewer B cells, NK cells, and Treg cells with an effector/memory phenotype were detected in the adenoids of AR children, and these lower percentages of immune cells, particularly CSMBs, were closely linked to aeroallergen sensitization models and respiratory viral infection.

Mechanisms underlying immunosuppression by regulatory cells

Regulatory cells, such as regulatory T cells (Tregs), regulatory B cells (Bregs), and myeloid-derived suppressor cells (MDSCs), play a crucial role in preserving immune tolerance and controlling immune responses during infections to prevent excessive immune activation. However, pathogens have developed strategies to hijack these regulatory cells to decrease the overall effectiveness of the immune response and persist within the host. Consequently, therapeutic targeting of these immunosuppressive mechanisms during infection can reinvigorate the immune response and improve the infection outcome. The suppressive mechanisms of regulatory cells are not only numerous but also redundant, reflecting the complexity of the regulatory network in modulating the immune responses. The context of the immune response, such as the type of pathogen or tissue involved, further influences the regulatory mechanisms involved. Examples of these immunosuppressive mechanisms include the production of inhibitory cytokines such as interleukin 10 (IL-10) and transforming growth factor beta (TGF-β) that inhibit the production of pro-inflammatory cytokines and dampen the activation and proliferation of effector T cells. In addition, regulatory cells utilize inhibitory receptors like cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) to engage with their respective effector cells, thereby suppressing their function. An alternative approach involves the modulation of metabolic reprogramming in effector immune cells to limit their activation and proliferation. In this review, we provide an overview of the major mechanisms mediating the immunosuppressive effect of the different regulatory cell subsets in the context of infection.

A novel Streptococcus pneumoniae human challenge model demonstrates Treg lymphocyte recruitment to the infection site

To investigate local tissue responses to infection we have developed a human model of killed Streptococcus pneumoniae challenge by intradermal injection into the forearm. S. pneumoniae intradermal challenge caused an initial local influx of granulocytes and increases in TNF, IL6 and CXCL8. However, by 48 h lymphocytes were the dominant cell population, mainly consisting of CD4 and CD8 T cells. Increases in local levels of IL17 and IL22 and the high proportion of CD4 cells that were CCR6⁺ suggested a significant Th17 response. Furthermore, at 48 h the CD4 population contained a surprisingly high proportion of likely memory Treg cells (CCR6 positive and CD45RA negative CD4⁺CD25^highCD127^low cells) at 39%. These results demonstrate that the intradermal challenge model can provide novel insights into the human response to S. pneumoniae and that Tregs form a substantial contribution of the normal human lymphocyte response to infection with this important pathogen.

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

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

Infection with SARS-CoV-2 primes immunological memory in human nasal-associated lymphoid tissue

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, has resulted in considerable morbidity and mortality in humans. Little is known regarding the development of immunological memory following SARS-CoV-2 infection or whether immunological memory can provide long-lasting protection against reinfection. Urgent need for vaccines is a considerable issue for all governments worldwide.

METHODS

A total of 39 patients were recruited in this study. Tonsillar mononuclear cells (MNCs) were co-cultured in RPMI medium and stimulated with the full-length SARS-CoV-2 spike protein in the presence and absence of a CpG-DNA adjuvant. An enzyme-linked immunosorbent assay (ELISA) was utilised to measure the specific antibody response to the spike protein in the cell culture supernatants.

RESULTS

The SARS-CoV-2 spike protein primed a potent memory B cell-mediated immune response in nasal-associated lymphoid tissue (NALT) from patients previously infected with the virus. Additionally, spike protein combined with the CpG-DNA adjuvant induced a significantly increased level of specific anti-spike protein IgG antibody compared with the spike protein alone (p < 0.0001, n = 24). We also showed a strong positive correlation between the specific anti-spike protein IgG antibody level in a serum samples and that produced by MNCs derived from the same COVID-19-recovered patients following stimulation (r = 0.76, p = 0.0002, n = 24).

CONCLUSION

Individuals with serological evidence of previous SARS-CoV-2 exposure showed a significant anti-spike protein-specific memory humoral immune response to the viral spike protein upon stimulation. Additionally, our results demonstrated the functional response of NALT-derived MNCs to the viral spike protein. CpG-DNA adjuvant combined with spike protein induced significantly stronger humoral immune responses than the spike protein alone. These data indicate that the S protein antigen combined with CpG-DNA adjuvant could be used as a future vaccine candidate.

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

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

In vitro cell culture model of human nasal-associated lymphoid tissue (NALT) to evaluate the humoral immune response to SARS-CoV-2 spike proteins

To date, coronavirus disease 2019 (COVID-19) continues to be considered a pandemic worldwide, with a mild to severe disease presentation that is sometimes associated with serious complications that are concerning to global health authorities. Scientists are working hard to understand the pathogenicity of this novel virus, and a great deal of attention and effort has been focused on identifying therapeutics and vaccines to control this pandemic.

Methods

This study used tonsils removed from twelve patients who underwent an elective tonsillectomy in the ear, nose, and throat (ENT) department at Saudi Germany Hospital, Madinah, Saudi Arabia. Tonsillar mononuclear cells (MNCs) were separated and co-cultured in RPMI complete medium in the presence and absence of viral spike (S) proteins (the full-length S, S1 subunit, and S2 subunit proteins). Enzyme-linked immunosorbent assay (ELISA) was used to measure secreted antibody concentrations following stimulation.

Results

The in vitro human nasal-associated lymphoid tissue (NALT) cell culture model was successfully used to evaluate the humoral immune response against SARS-CoV-2- S protein. Significant (p < 0.0001, n = 12) levels of specific, anti-S IgG, IgM, and IgA antibody responses were detected in cells culture supernatanat folloeing stimulation with the full-length S protein compared with unstimulated cells. In contrast, S1 and S2 subunit proteins alone failed to induce a mucosal humoral immune response following tonsillar MNC stimulation.

Conclusion

We demonstrated a successful human NALT in vitro cell culture model that was used to study the mucosal humoral immune response to the SARS-CoV-2 S protein. This model could be advantageous for the in-depth study of cellular immune responses to the S protein and other viral antigens, such as nucleocapsid and matrix antigen. The S protein appears to be the important viral protein that may be able to mimic the natural infection process intranasally and should be studied as a component of a candidate vaccine.

Acute bacterial meningitis

Purpose of review

Community-acquired bacterial meningitis is a continually changing disease. This review summarises both dynamic epidemiology and emerging data on pathogenesis. Updated clinical guidelines are discussed, new agents undergoing clinical trials intended to reduce secondary brain damage are presented.

Recent findings

Conjugate vaccines are effective against serotype/serogroup-specific meningitis but vaccine escape variants are rising in prevalence. Meningitis occurs when bacteria evade mucosal and circulating immune responses and invade the brain: directly, or across the blood–brain barrier. Tissue damage is caused when host genetic susceptibility is exploited by bacterial virulence. The classical clinical triad of fever, neck stiffness and headache has poor diagnostic sensitivity, all guidelines reflect the necessity for a low index of suspicion and early Lumbar puncture. Unnecessary cranial imaging causes diagnostic delays. cerebrospinal fluid (CSF) culture and PCR are diagnostic, direct next-generation sequencing of CSF may revolutionise diagnostics. Administration of early antibiotics is essential to improve survival. Dexamethasone partially mitigates central nervous system inflammation in high-income settings. New agents in clinical trials include C5 inhibitors and daptomycin, data are expected in 2025.

Summary

Clinicians must remain vigilant for bacterial meningitis. Constantly changing epidemiology and emerging pathogenesis data are increasing the understanding of meningitis. Prospects for better treatments are forthcoming.

Understanding host immune responses to pneumococcal proteins in the upper respiratory tract to develop serotype-independent pneumococcal vaccines

Introduction: Nasopharyngeal colonization is a precondition for mucosal and invasive pneumococcal disease. Prevention of colonization may reduce pneumococcal transmission and disease incidence. Therefore, several protein-based pneumococcal vaccines are currently under investigation. Areas covered: We aimed to better understand the host immune responses to pneumococcal proteins in the upper respiratory tract (URT) that could facilitate the development of serotype-independent pneumococcal vaccines. English peer-reviewed papers reporting immunological mechanisms involved in host immune response to pneumococcal proteins in the URT were retrieved through a PubMed search using the terms 'pneumococcal proteins,' 'nasopharyngeal colonization' and/or 'cellular/humoral host immune response.' Expert opinion: Although pneumococcal protein antigens induce humoral immune responses, as well as IL-17A-mediated immunity, none of them, when used as single antigen, is sufficient to control and broadly protect against pneumococcal colonization. Novel vaccines should contain multiple conserved protein antigens to activate both arms of the immune system and evoke protection against the whole spectrum of pneumococcal variants by reducing, rather than eradicating, pneumococcal carriage. The highest efficacy would likely be achieved when the vaccine is intranasally applied, inducing mucosal immunity and enhancing the first line of defense by restricting pneumococcal density in the URT, which in turn will lead to reduced transmission and protection against disease.

A Phase 1 Randomized, Placebo-controlled, Observer-blinded Trial to Evaluate the Safety and Immunogenicity of Inactivated Streptococcus pneumoniae Whole-cell Vaccine in Adults

BACKGROUND

Broadly protective pneumococcal vaccines that are affordable for low-resource countries are needed. Streptococcus pneumoniae whole cell vaccine (wSp) is an investigational vaccine that contains killed cells from a nonencapsulated strain of S. pneumoniae (SPn) with aluminum hydroxide adjuvant. Studies in mice demonstrated protection against nasopharyngeal carriage (T-cell-mediated) and invasive pneumococcal disease (antibody-mediated). The aim of this randomized, double-blind, placebo-controlled Phase 1 study was to assess safety, tolerability and immunogenicity of wSp in healthy adults.

METHODS

Forty-two participants were randomized into 3 dose cohorts to receive 0.1, 0.3, or 0.6 mg of wSp or saline intramuscularly. Participants received a 3-dose vaccination schedule spaced by 4-week intervals. Postvaccination assessments included solicited reactogenicity events through day 7, blood chemistry and hematology assessments at day 7, and adverse events (AEs) through day 84. Participants were monitored for serum antibody and peripheral blood mononuclear cell cytokine responses to pneumococcal antigens. A 6-month telephone follow-up was completed to assess for any additional AEs.

RESULTS

wSp was safe and well tolerated. Reactogenicity was acceptable and no untoward safety signals were observed. wSp elicited potentially clinically significant rises (defined arbitrarily as at least a 2-fold rise) in immunoglobulin G responses to multiple pneumococcal antigens, including pneumococcal surface protein A and pneumolysin. Functional antibody responses were observed with the highest dose of wSp (0.6 mg). Increases in T-cell cytokine responses, including interleukin 17A, were also seen among wSp vaccines.

CONCLUSIONS

wSp was safe and well tolerated in healthy US adults, eliciting pneumococcal antigen-specific antibody and T-cell cytokine responses.

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

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

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

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

Microinvasion by Streptococcus pneumoniae induces epithelial innate immunity during colonisation at the human mucosal surface

Control of Streptococcus pneumoniae colonisation at human mucosal surfaces is critical to reducing the burden of pneumonia and invasive pneumococcal disease, interrupting transmission, and achieving herd protection. Here, we use an experimental human pneumococcal carriage model (EHPC) to show that S. pneumoniae colonisation is associated with epithelial surface adherence, micro-colony formation and invasion, without overt disease. Interactions between different strains and the epithelium shaped the host transcriptomic response in vitro. Using epithelial modules from a human epithelial cell model that recapitulates our in vivo findings, comprising of innate signalling and regulatory pathways, inflammatory mediators, cellular metabolism and stress response genes, we find that inflammation in the EHPC model is most prominent around the time of bacterial clearance. Our results indicate that, rather than being confined to the epithelial surface and the overlying mucus layer, the pneumococcus undergoes micro-invasion of the epithelium that enhances inflammatory and innate immune responses associated with clearance.

Streptococcus pneumoniae is a common coloniser of the human nasopharynx, but it also causes severe diseases. Here, Weight et al. use an experimental human pneumococcal carriage model to show that bacterial colonisation is associated with invasion of the epithelium and enhancement of immune responses.

Regulatory T lymphocytes are associated with increased nasopharyngeal colonization in children

OBJECTIVES

Regulatory T lymphocytes (T_reg) have been linked to survival of commensal bacteria at mucosal sites, but their presence and role in chronic otitis media (COM) and their response to otopathogens has not been evaluated previously. We investigated the association between T_reg lymphocytes and otopathogens in COM prone and non-COM prone children.

METHODS

Forty children, 2-7 years of age, scheduled for adenoidectomy were enrolled into COM (n = 20) or non-COM (n = 20) groups. Adenoid biopsy and nasopharyngeal aspirate bacteriology were assessed by conventional culture techniques. Peripheral blood and adenoid lymphocytes were stained with viability stain, monoclonal anti-CD19, anti-CD3, anti-CD4, anti-CD8, anti-CD25 and anti-CD127. Cells were stained intracellularly with monoclonal anti-FoxP3 and then quantified by flow cytometry.

RESULTS

Children with nasopharyngeal otopathogen-positive culture had significantly more circulating CD3⁺CD4⁺FoxP3⁺CD25^hi+CD127^lo+ lymphocytes (M = 4.4%) compared to culture-negative children (M = 3.1%, p = 0.005). Circulating CD19⁺ lymphocytes were significantly increased in children with positive Moraxella catarrhalis nasopharyngeal culture (M = 12.4%) compared to culture-negative children (M = 8.6%, p = 0.006). Adenoid-derived lymphocytes were not significantly different in children with any positive nasopharyngeal culture compared to negative culture. Lymphocyte subsets were not significantly different between COM and non-COM prone children.

CONCLUSION

Clinically-detectable otopathogen nasopharyngeal culture is positively associated with T_reg lymphocytes, potentially inducing suppressive effector responses to promote colonization and infection chronicity. This finding supports further investigation of T_reg lymphocyte activity and influence on upper airway colonization of young children.

Mechanisms of Naturally Acquired Immunity to Streptococcus pneumoniae

In this review we give an update on the mechanisms of naturally acquired immunity against Streptococcus pneumoniae, one of the major human bacterial pathogens that is a common cause of pneumonia, septicaemia, and meningitis. A clear understanding of the natural mechanisms of immunity to S. pneumoniae is necessary to help define why the very young and elderly are at high risk of disease, and for devising new prevention strategies. Recent data has shown that nasopharynx colonization by S. pneumoniae induces antibody responses to protein and capsular antigens in both mice and humans, and also induces Th17 CD4+ cellular immune responses in mice and increases pre-existing responses in humans. These responses are protective, demonstrating that colonization is an immunizing event. We discuss the data from animal models and humans on the relative importance of naturally acquired antibody and Th17 cells on immunity to S. pneumoniae at three different anatomical sites of infection, the nasopharynx (the site of natural asymptomatic carriage), the lung (site of pneumonia), and the blood (site of sepsis). Mouse data suggest that CD4+ Th17 cells prevent both primary and secondary nasopharyngeal carriage with no role for antibody induced by previous colonization. In contrast, antibody is necessary for prevention of sepsis but CD4+ cellular responses are not. Protection against pneumonia requires a combination of both antibody and Th17 cells, in both cases targeting protein rather than capsular antigen. Proof of which immune component prevents human infection is less easily available, but two recent papers demonstrate that human IgG targeting S. pneumoniae protein antigens is highly protective against septicaemia. The role of CD4+ responses to prior nasopharyngeal colonization for protective immunity in humans is unclear. The evidence that there is significant naturally-acquired immunity to S. pneumoniae independent of anti-capsular polysaccharide has clinical implications for the detection of subjects at risk of S. pneumoniae infections, and the data showing the importance of protein antigens as targets for antibody and Th17 mediated immunity should aid the development of new vaccine strategies.

Th17 responses to pneumococcus in blood and adenoidal cells in children

Pneumococcal infections cause a large global health burden, and the search for serotype-independent vaccines continues. Existing conjugate vaccines reduce nasopharyngeal colonization by target serotypes. Such mucosal effects of novel antigens may similarly be important. CD4+ Th17 cell-dependent, antibody-independent reductions in colonization and enhanced clearance have been described in mice. Here we describe the evaluation of T helper type 17 (Th17) cytokine responses to candidate pneumococcal protein vaccine antigens in human cell culture, using adenoidal and peripheral blood mononuclear cells. Optimal detection of interleukin (IL)-17A was at day 7, and of IL-22 at day 11, in these primary cell cultures. Removal of CD45RO+ memory T cells abolished these responses. Age-associated increases in magnitude of responses were evident for IL-17A, but not IL-22, in adenoidal cells. There was a strong correlation between individual IL-17A and IL-22 responses after pneumococcal antigen stimulation (P < 0·015). Intracellular cytokine staining following phorbol myristate acetate (PMA)/ionomycin stimulation demonstrated that  > 30% CD4+ T cells positive for IL-22 express the innate markers γδT cell receptor and/or CD56, with much lower proportions for IL-17A+ cells (P < 0·001). Responses to several vaccine candidate antigens were observed but were consistently absent, particularly in blood, to PhtD (P < 0·0001), an antigen recently shown not to impact colonization in a clinical trial of a PhtD-containing conjugate vaccine in infants. The data presented and approach discussed have the potential to assist in the identification of novel vaccine antigens aimed at reducing pneumococcal carriage and transmission, thus improving the design of empirical clinical trials.

IL-17A expression in the adenoid tissue from children with sleep disordered breathing and its association with pneumococcal carriage

Tonsil and adenoid-tissue hypertrophy (AH) is the most common cause of pediatric sleep-disordered breathing (SDB), with AH possibly initiated by repeated exposure to infectious agents or allergens. Here, we evaluated IL-17A activity in adenoid tissue from children with SDB and its association with AH and pneumococcal carriage. Thirty-five children (aged 3-12 years) with SDB and receiving adenoidectomy and tonsillectomy were enrolled. During surgery, nasopharyngeal carriage was determined by bacterial culture and multiplex PCR via nasopharyngeal swab, and adenoid samples were collected. IL-17A and associated cytokine expression was evaluated by real-time PCR and western blotting. The mRNA analysis showed that IL-17A level, IL-17A:IL-10 ratio, and RAR-related orphan receptor-γt:forkhead box P3 ratio were significantly higher in adenoid tissues with AH, as were IL-17A level and IL-17A:IL-10 ratio in adenoid tissues with pneumococcal carriage. Additionally, pneumococcal carriage was more common in nasopharyngeal adenoids from patients without AH than those with AH. IL-17A was upregulated in adenoid tissues from patients with AH and with pneumococcal carriage. These results suggested that pneumococcal carriage initiates an IL-17A-mediated immune response in nasopharyngeal adenoids, which might be associated with AH in patients with SDB.

Screening for Th17-Dependent Pneumococcal Vaccine Antigens: Comparison of Murine and Human Cellular Immune Responses

Conjugate vaccines against Streptococcus pneumoniae have significantly reduced the incidence of diseases caused by the serotypes included in those vaccines; however, there is still a need for vaccines that confer serotype-independent protection. In the current study, we have constructed a library of conserved surface proteins from S. pneumoniae and have screened for IL-17A and IL-22 production in human immune cells obtained from adenoidal/tonsillar tissues of children and IL-17A production in splenocytes from mice that had been immunized with a killed whole-cell vaccine or previously exposed to pneumococcus. A positive correlation was found between the rankings of proteins from human IL-17A and IL-22 screens, but not between those from human and mouse screens. All proteins were tested for protection against colonization, and we identified protective antigens that are IL-17A dependent. We found that the likelihood of finding a protective antigen is significantly higher for groups of proteins ranked in the top 50% of all three screens than for groups of proteins ranked in the bottom 50% of all three. The results thus confirmed the value of such screens for identifying Th17 antigens. Further, these experiments have evaluated and compared the breadth of human and mouse Th17 responses to pneumococcal colonization and have enabled the identification of potential vaccine candidates based on immunological responses in mouse and human cells.

Differential cellular composition of human palatine and pharyngeal tonsils

OBJECTIVE

The goal of this study was to gain a better understanding of the potential functional specialization of palatine and pharyngeal tonsils, by comparing their cellular composition in paired specimens from a large cohort of adenotonsillectomy patients.

DESIGN

Resident B cell, T cell, dendritic cell, and stromal cell subsets were characterized using multicolor flow cytometry in palatine and pharyngeal tonsil specimens from 27 patients, age 2-34 years.

RESULTS

Paired comparisons showed highly significant intra-individual differences in resident cell subsets of palatine and pharyngeal tonsils. Palatine tonsils harbored higher fractions of germinal center B cells/plasmablasts and IgD- CD27- double-negative B cells, and conversely lower fractions of IgD + CD38- resting naïve B cells compared to pharyngeal tonsils. Palatine tonsils also showed lower fractions of plasmacytoid dendritic cells, and higher percentages of two subsets of stromal cells - fibroblastic reticular cells and lymphatic endothelial cells - compared to pharyngeal tonsils from the same individual.

CONCLUSIONS

Despite their physical proximity and histological similarities, palatine and pharyngeal tonsils display marked intra-individual differences in their cellular composition with regard to functionally important immune and stromal subsets. These differences are likely to have immunologic, pathologic, and physiologic significance.

Activation and Induction of Antigen-Specific T Follicular Helper Cells Play a Critical Role in Live-Attenuated Influenza Vaccine-Induced Human Mucosal Anti-influenza Antibody Response

There is increasing interest recently in developing intranasal vaccines against respiratory tract infections. The antibody response is critical for vaccine-induced protection, and T follicular helper cells (T_FH) are considered important for mediating the antibody response. Most data supporting the role for T_FH in the antibody response are from animal studies, and direct evidence from humans is limited, apart from the presence of T_FH-like cells in blood. We studied the activation and induction of T_FH and their role in the anti-influenza antibody response induced by a live-attenuated influenza vaccine (LAIV) in human nasopharynx-associated lymphoid tissue (NALT). T_FH activation in adenotonsillar tissues was analyzed by flow cytometry, and anti-hemagglutinin (anti-HA) antibodies were examined following LAIV stimulation of tonsillar mononuclear cells (MNC). Induction of antigen-specific T_FH by LAIV was studied by flow cytometry analysis of induced T_FH and CD154 expression. LAIV induced T_FH proliferation, which correlated with anti-HA antibody production, and T_FH were shown to be critical for the antibody response. Induction of T_FH from naive T cells by LAIV was shown in newly induced T_FH expressing BCL6 and CD21, followed by the detection of anti-HA antibodies. Antigen specificity of LAIV-induced T_FH was demonstrated by expression of the antigen-specific T cell activation marker CD154 upon challenge by H1N1 virus antigen or HA. LAIV-induced T_FH differentiation was inhibited by BCL6, interleukin-21 (IL-21), ICOS, and CD40 signaling blocking, and that diminished anti-HA antibody production. In conclusion, we demonstrated the induction by LAIV of antigen-specific T_FH in human NALT that provide critical support for the anti-influenza antibody response. Promoting antigen-specific T_FH in NALT by use of intranasal vaccines may provide an effective vaccination strategy against respiratory infections in humans.

IMPORTANCE Airway infections, such as influenza, are common in humans. Intranasal vaccination has been considered a biologically relevant and effective way of immunization against airway infection. The vaccine-induced antibody response is crucial for protection against infection. Recent data from animal studies suggest that one type of T cells, T_FH, are important for the antibody response. However, data on whether T_FH-mediated help for antibody production operates in humans are limited due to the lack of access to human immune tissue containing T_FH. In this study, we demonstrate the induction of T_FH in human immune tissue, providing critical support for the anti-influenza antibody response, by use of an intranasal influenza vaccine. Our findings provide direct evidence that T_FH play a critical role in vaccine-induced immunity in humans and suggest a novel strategy for promoting such cells by use of intranasal vaccines against respiratory infections.

The immunological mechanisms that control pneumococcal carriage

Colonization of the human nasopharynx by pneumococcus is extremely common and is both the primary reservoir for transmission and a prerequisite for disease. Current vaccines targeting the polysaccharide capsule effectively prevent colonization, conferring herd protection within vaccinated communities. However, these vaccines cover only a subset of all circulating pneumococcal strains, and serotype replacement has been observed. Given the success of pneumococcal conjugate vaccine (PCV) in preventing colonization in unvaccinated adults within vaccinated communities, reducing nasopharyngeal colonization has become an outcome of interest for novel vaccines. Here, we discuss the immunological mechanisms that control nasopharyngeal colonization, with an emphasis on findings from human studies. Increased understanding of these immunological mechanisms is required to identify correlates of protection against colonization that will facilitate the early testing and design of novel vaccines.

Barriers to HIV remission research in low- and middle-income countries

INTRODUCTION

HIV eradication and remission research has largely taken place in high-income countries. In low- and middle-income countries (LMIC), there may be factors that have a substantial impact on the size of the latent HIV reservoir and the immunological response to infection. If a curative strategy is to be available to all HIV-infected individuals, these factors must be understood.

METHODS

We use a scoping review to examine the literature on biological factors that may have an impact on HIV persistence in LMIC. Three databases were searched without date restrictions.

RESULTS

Uncontrolled viral replication and higher coinfection prevalence may alter the immunological milieu of individuals in LMIC and increase the size of the HIV reservoir. Differences in HIV subtype could also influence the measurement and size of the HIV reservoir. Immune activation may differ due to late presentation to care, presence of chronic infections, increased gut translocation of bacterial products and poor nutrition.

CONCLUSIONS

Research on HIV remission is urgently needed in LMIC. Research into chronic immune activation in resource poor environments, the immune response to infection, the mechanisms of HIV persistence and latency in different viral clades and the effect of the microbiological milieu must be performed. Geographic differences, which may be substantial and may delay access to curative strategies, should be identified.

The contrasting roles of Th17 immunity in human health and disease

The human immune system is a tightly regulated network that protects the host from disease. An important aspect of this is the balance between pro-inflammatory Th17 cells and anti-inflammatory T regulatory (Treg) cells in maintaining immune homeostasis. Foxp3+ Treg are critical for sustaining immune tolerance through IL-10 and transforming growth factor-β while related orphan receptor-γt+ Th17 cells promote immunopathology and auto-inflammatory diseases through the actions of IL-17A, IL-21 and IL-22. Therefore, imbalance between Treg and Th17 cells can result in serious pathology in many organs and tissues. Recently, certain IL-17-producing cells have been found to be protective against infectious disease, particularly in relation to extracellular bacteria such Streptococcus pneumoniae; a number of other novel IL-17-secreting cell populations have also been reported to protect against a variety of other pathogens. In this mini-review, the dual roles of Treg and Th17 cells are discussed in the context of autoimmunity and infections, highlighting recent advances in the field. Development of novel strategies specifically designed to target these critical immune response pathways will become increasingly important in maintenance of human health.

Panel 5: Immunology

Objective

To perform a state-of-the-art review of the literature from January 2012 through May 2015 on studies that advanced our knowledge of the innate and adaptive immunology related to otitis media. This review also proposes future directions for research in this area.

Data Sources

PubMed database of the National Library of Medicine.

Review Methods

Three subpanels comprising experts in the field focused on sections relevant to cytokines, innate immunity, and adaptive immunity. The review focused on animal, cell line, and human studies and was critical in relation to the recommendations from the previous publication and for determination of the proposed goals and priorities. The panel met at the 18th International Symposium on Recent Advances in Otitis Media in June 2015 to consolidate its prior search results and discuss, plan, and refine the review. The panel approved the final draft.

Conclusion

From 2012 to 2014, tremendous progresses in immunology of otitis media were established—especially in the areas of innate immunity associated with the pathogenesis of otitis media.

Implications for Practice

The advances of the past 4 years formed the basis for a series of short- and long-term research goals in an effort to guide the field. Accomplishing these goals will provide opportunities for the development of novel interventions, including new ways to better treat and prevent otitis media, especially for recurrent otitis media.

A dynamic relationship between mucosal T helper type 17 and regulatory T-cell populations in nasopharynx evolves with age and associates with the clearance of pneumococcal carriage in humans

Pneumococcal carriage is common in young children, which may account for the high incidence of disease in this age group. Host factors determining the clearance of carriage in humans remain unclear. We aimed to study the relationships between T helper type 17 (Th17) and Foxp3(+) regulatory T (Treg) cells in nasopharynx-associated lymphoid tissue (NALT) and carriage in children and adults. Frequencies of Th17 and Treg cells in NALT were analysed by flow cytometry in association with age and pneumococcal carriage status. Cytokine responses following pneumococcal stimulation were analysed by cytometric beads array. The frequencies of Th17 and Treg cells in NALT were inversely correlated (R -0.60). Whereas Treg cell frequency decreased with age (R -0.63), both Th17 and the Th17: Treg ratio increased with age (R 0.62 and R 0.64, respectively). Also, the Th17: Treg ratio was higher in carriage-negative than in carriage-positive children (p <0.01). Pneumococcal stimulation of tonsillar cells increased both Th17 and Treg cell numbers, but the Th17: Treg ratio and pattern of cytokine responses differed between carriage-negative and carriage-positive children. The former showed markedly higher Th17: Treg and interleukin-17A: interleukin-10 ratios than in the latter (p <0.01). Pneumococcal stimulation also induces Th17, although the capacity of this Th17 differentiation from naive T cells of young children was low, but increased with age. We demonstrated a dynamic relationship between Th17 and Treg cells in human nasopharynx that evolves with age. The balance between Th17 and Treg cells in NALT appears to be a major host factor closely associated with the clearance of Streptococcus pneumoniae from the nasopharynx.

A critical role of T follicular helper cells in human mucosal anti-influenza response that can be enhanced by immunological adjuvant CpG-DNA

T Follicular helper cells (TFH) are considered critical for B cell antibody response, and recent efforts have focused on promoting TFH in order to enhance vaccine efficacy. We studied the frequency and function of TFH in nasopharynx-associated lymphoid tissues (NALT) from children and adults, and its role in anti-influenza antibody response following stimulation by a live-attenuated influenza vaccine (LAIV) or an inactivated seasonal virus antigen (sH1N1). We further studied whether CpG-DNA promotes TFH and by which enhances anti-influenza response. We showed NALT from children aged 1.5-10 years contained abundant TFH, suggesting efficient priming of TFH during early childhood. Stimulation by LAIV induced a marked increase in TFH that correlated with a strong production of anti-hemagglutinin (HA) IgA/IgG/IgM antibodies in tonsillar cells. Stimulation by the inactivated sH1N1 antigen induced a small increase in TFH which was markedly enhanced by CpG-DNA, accompanied by enhanced anti-HA antibody responses. In B cell co-culture experiment, anti-HA responses were only seen in the presence of TFH, and addition of plasmacytoid dendritic cell to TFH-B cell co-culture enhanced the TFH-mediated antibody production following CpG-DNA and sH1N1 antigen stimulation. Induction of TFH differentiation from naïve T cells was also shown following the stimulation. Our results support a critical role of TFH in human mucosal anti-influenza antibody response. Use of an adjuvant such as CpG-DNA that has the capacity to promote TFH by which to enhance antigen-induced antibody responses in NALT tissue may have important implications for future vaccination strategies against respiratory pathogens.

Immune Homeostatic Macrophages Programmed by the Bacterial Surface Protein NhhA Potentiate Nasopharyngeal Carriage of Neisseria meningitidis

Neisseria meningitidis colonizes the nasopharyngeal mucosa of healthy populations asymptomatically, although the bacterial surface is rich in motifs that activate the host innate immunity. What determines the tolerant host response to this bacterium in asymptomatic carriers is poorly understood. We demonstrated that the conserved meningococcal surface protein NhhA orchestrates monocyte (Mo) differentiation specifically into macrophage-like cells with a CD200R^hi phenotype (NhhA-Mφ). In response to meningococcal stimulation, NhhA-Mφ failed to produce proinflammatory mediators. Instead, they upregulated interleukin-10 (IL-10) and Th2/regulatory T cell (Treg)-attracting chemokines, such as CCL17, CCL18, and CCL22. Moreover, NhhA-Mφ were highly efficient in eliminating bacteria. The in vivo validity of these findings was corroborated using a murine model challenged with N. meningitidis systematically or intranasally. The NhhA-modulated immune response protected mice from septic shock; Mo/Mφ depletion abolished this protective effect. Intranasal administration of NhhA induced an anti-inflammatory response, which was associated with N. meningitidis persistence at the nasopharynx. In vitro studies demonstrated that NhhA-triggered Mo differentiation occurred upon engaged Toll-like receptor 1 (TLR1)/TLR2 signaling and extracellular signal-regulated kinase (ERK) and Jun N-terminal protein kinase (JNK) activation and required endogenously produced IL-10 and tumor necrosis factor alpha (TNF-α). Our findings reveal a strategy that might be adopted by N. meningitidis to maintain asymptomatic nasopharyngeal colonization.

Neisseria meningitidis is an opportunistic human-specific pathogen that colonizes the nasopharyngeal mucosa asymptomatically in approximately 10% of individuals. Very little is known about how this bacterium evades immune activation during the carriage stage. Here, we observed that N. meningitidis, via the conserved surface protein NhhA, skewed monocyte differentiation into macrophages with a CD200R^hi phenotype. Both in vivo and in vitro data demonstrated that these macrophages, upon meningococcal infection, played an important role in forming a homeostatic immune microenvironment through their capacity to eliminate invading bacteria and to generate anti-inflammatory mediators. This work provides novel insight into the mechanisms underlying the commensal persistence of N. meningitidis.

Next generation protein based Streptococcus pneumoniae vaccines

All currently available Streptococcus pneumoniae (Spn) vaccines have limitations due to their capsular serotype composition. Both the 23-valent Spn polysaccharide vaccine (PPV) and 7, 10, or 13-valent Spn conjugate vaccines (PCV-7, 10, -13) are serotype-based vaccines and therefore they elicit only serotype-specific immunity. Emergence of replacement Spn strains expressing other serotypes has consistently occurred following introduction of capsular serotype based Spn vaccines. Furthermore, capsular polysaccharide vaccines are less effective in protection against non-bacteremic pneumonia and acute otitis media (AOM) than against invasive pneumococcal disease (IPD). These shortcomings of capsular polysaccharide-based Spn vaccines have created high interest in development of non-serotype specific protein-based vaccines that could be effective in preventing both IPD and non-IPD infections. This review discusses the progress to date on development of Spn protein vaccine candidates that are highly conserved by all Spn strains, are highly conserved, exhibit maximal antigenicity and minimal reactogenicity to replace or complement the current capsule-based vaccines. Key to development of a protein based Spn vaccine is an understanding of Spn pathogenesis. Based on pathogenesis, a protein-based Spn vaccine should include one or more ingredients that reduce NP colonization below a pathogenic inoculum. Elimination of all Spn colonization may not be achievable or even advisable. The level of expression of a target protein antigen during pathogenesis is another key to the success of protein based vaccines.. As with virtually all currently licensed vaccines, production of a serum antibody response in response to protein based vaccines is anticipated to provide protection from Spn infections. A significant advantage that protein vaccine formulations can offer over capsule based vaccination is their potential benefits associated with natural priming and boosting to all strains of Spn. One of the most universal and comprehensive approaches of identifying novel vaccine candidates is the investigation of human sera from different disease stages of natural infections. Antigens that are robustly reactive in preliminary human serum screening constitute a pathogen-specific antigenome. This strategy has identified a number of Spn protein vaccine candidates that are moving forward in human clinical trials.

Reduced IL-17A Secretion Is Associated with High Levels of Pneumococcal Nasopharyngeal Carriage in Fijian Children

Streptococcus pneumonia (the pneumococcus) is the leading vaccine preventable cause of serious infections in infants under 5 years of age. The major correlate of protection for pneumococcal infections is serotype-specific IgG antibody. More recently, antibody-independent mechanisms of protection have also been identified. Preclinical studies have found that IL-17 secreting CD4+ Th17 cells in reducing pneumococcal colonisation. This study assessed IL-17A levels in children from Fiji with high and low pneumococcal carriage density, as measured by quantitative real-time PCR (qPCR). We studied Th17 responses in 54 children who were designated as high density carriers (N=27, >8.21x10⁵ CFU/ml) or low density carriers (N=27, <1.67x10⁵ CFU/ml). Blood samples were collected, and isolated peripheral blood mononuclear cells (PBMCs) were stimulated for 6 days. Supernatants were harvested for cytokine analysis by multiplex bead array and/or ELISA. Th17 cytokines assayed included IL-17A, IL-21, IL-22 as well as TNF-α, IL-10, TGF-β, IL-6, IL-23 and IFNγ. Cytokine levels were significantly lower in children with high density pneumococcal carriage compared with children with low density carriage for IL-17A (p=0.002) and IL-23 (p=0.04). There was a trend towards significance for IL-22 (p=0.057) while no difference was observed for the other cytokines. These data provide further support for the role of Th17-mediated protection in humans and suggest that these cytokines may be important in the defence against pneumococcal carriage.

Delayed reconstitution of B cell immunity to pneumococcus in HIV-infected Malawian children on antiretroviral therapy

OBJECTIVE

Despite CD4(+) count restoration and viral load suppression with antiretroviral therapy (ART), HIV-infected children remain at increased risk of life-threatening infections including invasive pneumococcal disease (IPD). We therefore investigated whether persistent susceptibility to IPD following ART is associated with incomplete recovery of B-cell function.

METHODS

41 HIV-infected Malawian children commencing ART were followed-up for a 1 year period during which time blood samples were collected at 0, 3, 6 and 12 months for comprehensive immunophenotyping and pneumomococcal-specific Memory B-cell Enzyme-Linked Immunospot assays. In addition, nasopharyngeal swab samples were cultured to determine pneumococcal carriage rates.

RESULTS

Normalization of major lymphocyte subsets such as CD4(+) percentages was evident following 3 months of ART. The proportions of mature naïve B cells (CD19(+) CD10(-) CD27(-) CD21(hi)) and resting memory B cells (CD19(+) CD27(+) CD21(hi)) increased and apoptosis-prone mature activated B cells (CD19(+) CD21(lo) CD10(-)) decreased markedly by 12 months. However, in the context of high nasopharyngeal pneumococcal carriage rates (83%), restoration of pneumococcal protein antigen-specific B-cell memory was more delayed.

CONCLUSIONS

These data show that, in chronically HIV-infected children receiving ART, improvement in B-cell memory profiles and function is slower than CD4(+) T-cells. This supports early initiation of ART and informs research into optimal timing of immunization with pneumococcal vaccines.

Protection against Streptococcus pneumoniae lung infection after nasopharyngeal colonization requires both humoral and cellular immune responses

Streptococcus pneumoniae is a common cause of pneumonia and infective exacerbations of chronic lung disease, yet there are few data on how adaptive immunity can specifically prevent S. pneumoniae lung infection. We have used a murine model of nasopharyngeal colonization by the serotype 19F S. pneumoniae strain EF3030 followed by lung infection to investigate whether colonization protects against subsequent lung infection and the mechanisms involved. EF3030 colonization induced systemic and local immunoglobulin G against a limited number of S. pneumoniae protein antigens rather than capsular polysaccharide. During lung infection, previously colonized mice had increased early cytokine responses and neutrophil recruitment and reduced bacterial colony-forming units in the lungs and bronchoalveolar lavage fluid compared with control mice. Colonization-induced protection was lost when experiments were repeated in B-cell- or neutrophil-deficient mice. Furthermore, the improved interleukin (IL)-17 response to infection in previously colonized mice was abolished by depletion of CD4+ cells, and prior colonization did not protect against lung infection in mice depleted of CD4+ cells or IL17. Together these data show that naturally acquired protective immunity to S. pneumoniae lung infection requires both humoral and cell-mediated immune responses, providing a template for the design of improved vaccines that can specifically prevent pneumonia or acute bronchitis.

Association of Pneumococcal Carriage and Expression of Foxp3+ Regulatory T Cells and Th17 Cells in the Adenoids of Children

BACKGROUND

Pneumococcal carriage in the nasopharynx is a primary means of transmission and a necessary prerequisite for pneumococcal disease.

OBJECTIVES

We analyzed the relationship between expressions of Foxp3+ regulatory T (Treg) cells and Th17 cells, and pneumococcal carriage in the adenoids of children who were either positive or negative for pneumococci.

METHODS

We collected adenoidal tissue and nasopharyngeal swab samples from children undergoing an adenoidectomy. Adenoidal mononuclear cells were isolated, cultured and then stimulated with culture concentrated supernatant (CCS) obtained from a D39 bacterial strain.

RESULTS

Foxp3+ Treg cells were upregulated and Th17 cells were downregulated in populations of adenoidal mononuclear cells obtained from the pneumococcus-positive group. Following CCS stimulation, the increment in Foxp3+ Treg cells in the pneumococcus-positive group was significantly greater than that in the pneumococcus-negative group, while the increment in Th17 cells was less as compared to that in the pneumococcus-negative group. These results were consistent with variations in levels of Foxp3 mRNA and retinoic acid receptor-related orphan receptor-γt mRNA in adenoidal mononuclear cells. Levels of IL-17A and IL-6 in adenoid tissue were higher in the pneumococcus-negative group, and the levels of TGF-β in adenoid tissue were lower in the pneumococcus-negative group compared to the pneumococcus-positive group. Pneumococcal carriage in children was closely associated with the expressions of Foxp3+ Treg and Th17 cells in the adenoid.

CONCLUSION

Upregulation of Foxp3+ Treg cells might downregulate the production of Th17 cells in the adenoid, resulting in decreased scavenging of Streptococcus pneumoniae and chronic pneumococcal carriage.

Middle Ear and Eustachian Tube Mucosal Immunology

Mucosal immune responses within the middle ear and eustachian tube generally provide an effective and efficient response to the presence of microbial pathogens, with approximately 80% of clinically recognizable middle ear infections resolved within 7 days. Particularly for young children aged less than 3 years of age, the proximity and direct connection of the middle ear, via the eustachian tube, to the nasopharynx provide increased risk of commensal bacteria and upper respiratory tract viruses infecting the middle ear. Mucosal immunological defense in the middle ear and eustachian tube utilizes a number of mechanisms, including physicochemical barriers of mucus and the mucosal epithelial cells and innate immune responses such as inflammation, cellular infiltration, effusion, and antimicrobial protein secretions, in addition to adaptive host immune responses. Recent advances in otopathogen recognition via microbial pattern recognition receptors and elucidation of complex signaling cascades have improved understanding of the coordination and regulation of the middle ear mucosal response. These advances support vaccine development aiming to reduce the risk of otitis media in children.

Density and duration of pneumococcal carriage is maintained by transforming growth factor β1 and T regulatory cells

RATIONALE

Nasopharyngeal carriage of Streptococcus pneumoniae is a prerequisite for invasive disease, but the majority of carriage episodes are asymptomatic and self-resolving. Interactions determining the development of carriage versus invasive disease are poorly understood but will influence the effectiveness of vaccines or therapeutics that disrupt nasal colonization.

OBJECTIVES

We sought to elucidate immunological mechanisms underlying noninvasive pneumococcal nasopharyngeal carriage.

METHODS

Pneumococcal interactions with human nasopharyngeal and bronchial fibroblasts and epithelial cells were investigated in vitro. A murine model of nasopharyngeal carriage and an experimental human pneumococcal challenge model were used to characterize immune responses in the airways during carriage.

MEASUREMENTS AND MAIN RESULTS

We describe the previously unknown immunological basis of noninvasive carriage and highlight mechanisms whose perturbation may lead to invasive disease. We identify the induction of active transforming growth factor (TGF)-β1 by S. pneumoniae in human host cells and highlight the key role for TGF-β1 and T regulatory cells in the establishment and maintenance of nasopharyngeal carriage in mice and humans. We identify the ability of pneumococci to drive TGF-β1 production from nasopharyngeal cells in vivo and show that an immune tolerance profile, characterized by elevated TGF-β1 and high nasopharyngeal T regulatory cell numbers, is crucial for prolonged carriage of pneumococci. Blockade of TGF-β1 signaling prevents prolonged carriage and leads to clearance of pneumococci from the nasopharynx.

CONCLUSIONS

These data explain the mechanisms by which S. pneumoniae colonize the human nasopharynx without inducing damaging host inflammation and provide insight into the role of bacterial and host constituents that allow and maintain carriage.

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.

Impaired serotype-specific immune function following pneumococcal vaccination in infants with prior carriage

The impact of prior nasopharyngeal carriage on serotype-specific IgG responses following immunization with pneumococcal conjugate vaccines (PCV) has recently been described. This report extends these findings to describe the attenuation of functional immune responses following 23-valent pneumococcal polysaccharide vaccination (PPS). We report the attenuation of immune responses following booster with the 23-valent pneumococcal polysaccharide vaccination (PPS) in infants with prior nasopharyngeal carriage of Streptococcus pneumoniae. Fijian infants who were part of a phase II randomized, controlled trial of reduced dose PCV7 schedules were the basis of this study. Pneumococcal carriage was determined at 6, 9 and 12 months of age, prior to PPS immunization. Serum samples collected at 18 weeks (post-PCV7), 12 months (pre-PPS), 12.5 months and 17 months (post-PPS) of age were assessed for serotype-specific IgG and opsonophagocytic responses. The most frequently carried serotypes were 6B (N=11), 19F (N=14) and 23F (N=23). Significantly lower serotype-specific IgG for 19F, 23F but not 6B post-PPS were detected in infants with homologous serotype carriage prior to PPS compared with non-carriers (N=230). However, OPA levels for 6B and 23F were lower in infants that carried these serotypes. Pneumococcal carriage with 19F or 23F at any time prior to PPS immunization in infants at 12 months of age who were previously primed with PCV resulted in serotype-specific hyporesponsiveness that persisted until 17 months of age. These results may have implications for the timing of infant vaccine schedules, particularly in high disease burden settings.

Characterization of inflammatory responses during intranasal colonization with Streptococcus pneumoniae

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite to invasion to the lungs or bloodstream(1). This organism is capable of colonizing the mucosal surface of the nasopharynx, where it can reside, multiply and eventually overcome host defences to invade to other tissues of the host. Establishment of an infection in the normally lower respiratory tract results in pneumonia. Alternatively, the bacteria can disseminate into the bloodstream causing bacteraemia, which is associated with high mortality rates(2), or else lead directly to the development of pneumococcal meningitis. Understanding the kinetics of, and immune responses to, nasopharyngeal colonization is an important aspect of S. pneumoniae infection models. Our mouse model of intranasal colonization is adapted from human models(3) and has been used by multiple research groups in the study of host-pathogen responses in the nasopharynx(4-7). In the first part of the model, we use a clinical isolate of S. pneumoniae to establish a self-limiting bacterial colonization that is similar to carriage events in human adults. The procedure detailed herein involves preparation of a bacterial inoculum, followed by the establishment of a colonization event through delivery of the inoculum via an intranasal route of administration. Resident macrophages are the predominant cell type in the nasopharynx during the steady state. Typically, there are few lymphocytes present in uninfected mice(8), however mucosal colonization will lead to low- to high-grade inflammation (depending on the virulence of the bacterial species and strain) that will result in an immune response and the subsequent recruitment of host immune cells. These cells can be isolated by a lavage of the tracheal contents through the nares, and correlated to the density of colonization bacteria to better understand the kinetics of the infection.

Staphylococcus aureus Colonization: Modulation of Host Immune Response and Impact on Human Vaccine Design

In apparent contrast to its invasive potential Staphylococcus aureus colonizes the anterior nares of 20–80% of the human population. The relationship between host and microbe appears particularly individualized and colonization status seems somehow predetermined. After decolonization, persistent carriers often become re-colonized with their prior S. aureus strain, whereas non-carriers resist experimental colonization. Efforts to identify factors facilitating colonization have thus far largely focused on the microorganism rather than on the human host. The host responds to S. aureus nasal colonization via local expression of anti-microbial peptides, lipids, and cytokines. Interplay with the co-existing microbiota also influences colonization and immune regulation. Transient or persistent S. aureus colonization induces specific systemic immune responses. Humoral responses are the most studied of these and little is known of cellular responses induced by colonization. Intriguingly, colonized patients who develop bacteremia may have a lower S. aureus-attributable mortality than their non-colonized counterparts. This could imply a staphylococcal-specific immune “priming” or immunomodulation occurring as a consequence of colonization and impacting on the outcome of infection. This has yet to be fully explored. An effective vaccine remains elusive. Anti-S. aureus vaccine strategies may need to drive both humoral and cellular immune responses to confer efficient protection. Understanding the influence of colonization on adaptive response is essential to intelligent vaccine design, and may determine the efficacy of vaccine-mediated immunity. Clinical trials should consider colonization status and the resulting impact of this on individual patient responses. We urgently need an increased appreciation of colonization and its modulation of host immunity.

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.

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.

Infection with 2009 H1N1 influenza virus primes for immunological memory in human nose-associated lymphoid tissue, offering cross-reactive immunity to H1N1 and avian H5N1 viruses

Influenza is a highly contagious mucosal infection in the respiratory tract. The 2009 pandemic H1N1 (pH1N1) influenza virus infection resulted in substantial morbidity and mortality in humans. Little is known on whether immunological memory develops following pH1N1 infection and whether it provides protection against other virus subtypes. An enzyme-linked immunosorbent spot assay was used to analyze hemagglutinin (HA)-specific memory B cell responses after virus antigen stimulation in nose-associated lymphoid tissues (NALT) from children and adults. Individuals with serological evidence of previous exposure to pH1N1 showed significant cross-reactive HA-specific memory B cell responses to pH1N1, seasonal H1N1 (sH1N1), and avian H5N1 (aH5N1) viruses upon pH1N1 virus stimulation. pH1N1 virus antigen elicited stronger cross-reactive memory B cell responses than sH1N1 virus. Intriguingly, aH5N1 virus also activated cross-reactive memory responses to sH1N1 and pH1N1 HAs in those who had previous pH1N1 exposure, and that correlated well with the memory response stimulated by pH1N1 virus antigen. These memory B cell responses resulted in cross-reactive neutralizing antibodies against sH1N1, 1918 H1N1, and aH5N1 viruses. The 2009 pH1N1 infection appeared to have primed human host with B cell memory in NALT that offers cross-protective mucosal immunity to not only H1N1 but also aH5N1 viruses. These findings may have important implications for future vaccination strategies against influenza. It will be important to induce and/or enhance such cross-protective mucosal memory B cells.

Experimental human pneumococcal carriage augments IL-17A-dependent T-cell defence of the lung

Pneumococcal carriage is both immunising and a pre-requisite for mucosal and systemic disease. Murine models of pneumococcal colonisation show that IL-17A-secreting CD4(+) T-cells (Th-17 cells) are essential for clearance of pneumococci from the nasopharynx. Pneumococcal-responding IL-17A-secreting CD4(+) T-cells have not been described in the adult human lung and it is unknown whether they can be elicited by carriage and protect the lung from pneumococcal infection. We investigated the direct effect of experimental human pneumococcal nasal carriage (EHPC) on the frequency and phenotype of cognate CD4(+) T-cells in broncho-alveolar lavage and blood using multi-parameter flow cytometry. We then examined whether they could augment ex vivo alveolar macrophage killing of pneumococci using an in vitro assay. We showed that human pneumococcal carriage leads to a 17.4-fold (p = 0.007) and 8-fold (p = 0.003) increase in the frequency of cognate IL-17A(+) CD4(+) T-cells in BAL and blood, respectively. The phenotype with the largest proportion were TNF(+)/IL-17A(+) co-producing CD4(+) memory T-cells (p<0.01); IFNγ(+) CD4(+) memory T-cells were not significantly increased following carriage. Pneumococci could stimulate large amounts of IL-17A protein from BAL cells in the absence of carriage but in the presence of cognate CD4(+) memory T-cells, IL-17A protein levels were increased by a further 50%. Further to this we then show that alveolar macrophages, which express IL-17A receptors A and C, showed enhanced killing of opsonised pneumococci when stimulated with rhIL-17A (p = 0.013). Killing negatively correlated with RC (r = -0.9, p = 0.017) but not RA expression. We conclude that human pneumococcal carriage can increase the proportion of lung IL-17A-secreting CD4(+) memory T-cells that may enhance innate cellular immunity against pathogenic challenge. These pathways may be utilised to enhance vaccine efficacy to protect the lung against pneumonia.

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.

Regulation of naturally acquired mucosal immunity to Streptococcus pneumoniae in healthy Malawian adults and children

Worldwide, invasive pneumococcal disease caused by Streptococcus pneumoniae is most common in young children. In adults, disease rates decline following intermittent colonization and the acquisition of naturally acquired immunity. We characterized mucosal and systemic pneumococcal-specific T-cell responses in African children and adults who contend with intense rates of colonization, up to 100% and 60% respectively. We find most Malawian children have high pneumococcal-specific T-cell responses in tonsil tissue and peripheral blood. In addition, frequent commensalism generates CD25(hi) (Tregs) which modulate mucosal pneumococcal-specific T-cell responses in some children and ≥50% of adults. We propose that immune regulation may prolong pneumococcal colonization and predispose vulnerable individuals to disease.

Adenoidectomy in young children and serum IgG antibodies to pneumococcal surface protein A and choline binding protein A

OBJECTIVE

We have previously reported that surgical removal of the nasopharyngeal adenoid in young children resulted in increased risk of nasopharyngeal colonization by pneumococci. We now investigated whether adenoidectomy influences the development of serum IgG antibodies to pneumococcal choline-binding protein A (CbpA) and pneumococcal surface protein A (PspA).

METHODS

Altogether 217 children aged 12-48 months who had recurrent or persistent otitis media were randomized to undergo or not to undergo adenoidectomy. All the children underwent insertion of tympanostomy tubes. 166 children were followed-up for 3 years. The main outcome measures were concentrations of serum IgG antibodies to CbpA and PspA three years after randomization. Nasopharyngeal colonization by pneumococci was assessed 1, 2, and 3 years after randomization.

RESULTS

Adenoidectomy decreased concentrations of CbpA antibodies by ca. 25% independently of the observed increase in pneumococcal carriage (OR of log(10) transformed concentrations 0.74, 95% CI 0.58-0.94, P=0.016). Concentrations of PspA antibodies were lower and they seemed not to be influenced by adenoidectomy.

CONCLUSIONS

Adenoidectomy in young children causes a small but detectable impairment in the development of serum IgG antibodies to pneumococcal CbpA. The adenoid seems to have a role in augmenting systemic immunity against pneumococci.

Pharyngeal microflora disruption by antibiotics promotes airway hyperresponsiveness after respiratory syncytial virus infection

BACKGROUND

Regulatory T cells (Treg cells), which are essential for regulation of immune response to respiratory syncytial virus (RSV) infection, are promoted by pharyngeal commensal pneumococcus. The effects of pharyngeal microflora disruption by antibiotics on airway responsiveness and relative immune responses after RSV infection have not been clarified.

METHODS

Female BALB/c mice (aged 3 weeks) were infected with RSV and then treated with either oral antibiotics or oral double distilled water (ddH(2)O) from 1 d post infection (pi). Changes in pharyngeal microflora were analyzed after antibiotic treatment for 7 d and 14 d. At 8 d pi and 15 d pi, the inflammatory cells in bronchoalveolar lavage fluid (BALF) were investigated in combination with tests of pulmonary histopathology, airway hyperresponsiveness (AHR), pulmonary and splenic Treg cells responses. Pulmonary Foxp3 mRNA expression, IL-10 and TGF-β1 in BALF and lung homogenate were investigated at 15 d pi. Ovalbumin (OVA) challenge was used to induce AHR after RSV infection.

RESULTS

The predominant pharyngeal commensal, Streptococcus, was cleared by antibiotic treatment for 7 d. Same change also existed after antibiotic treatment for 14 d. After RSV infection, AHR was promoted by antibiotic treatment at 15 d pi. Synchronous decreases of pulmonary Treg cells, Foxp3 mRNA and TGF-β1 were detected. Similar results were observed under OVA challenge.

CONCLUSIONS

After RSV infection, antibiotic treatment cleared pharyngeal commensal bacteria such as Streptococcus, which consequently, might induce AHR and decrease pulmonary Treg cells.