Oral Fucoidan Attenuates Lung Pathology and Clinical Signs in a Severe Influenza a Mouse Model.

Fucoidans are known to be effective inhibitors of inflammation, and of virus binding and cellular entry. Undaria pinnatifida-derived fucoidan (UPF) was assessed in a severe influenza A (H1N1, PR8) infection model in mice. Initially, UPF was gavaged at 3.52 mg daily in a treatment model. Gross lung pathology (consolidation) was significantly reduced as compared to controls. UPF was then presented as a feed supplement at a rate of either nil, 3.52 mg/day or 7.04 mg/day in a prophylactic model, dosed three days before infection. A significant improvement was observed in the clinical signs of ill-health, as well as a reduction in gross lung pathology in animals treated with the higher dose, although there was no significant reduction in lung viral titres.

A Modular Vaccine Platform Combining Self-Assembled Peptide Cages and Immunogenic Peptides.

Subunit vaccines use delivery platforms to present minimal antigenic components for immunization. The benefits of such systems include multivalency, self-adjuvanting properties, and more specific immune responses. Previously, the design, synthesis, and characterization of self-assembling peptide cages (SAGEs) have been reported. In these, de novo peptides are combined to make hubs that assemble into nanoparticles when mixed in aqueous solution. Here it is shown that SAGEs are nontoxic particles with potential as accessible synthetic peptide scaffolds for the delivery of immunogenic components. To this end, SAGEs functionalized with the model antigenic peptides tetanus toxoid632-651 and ovalbumin323-339 drive antigen-specific responses both in vitro and in vivo, eliciting both CD4+ T cell and B cell responses. Additionally, SAGEs functionalized with the antigenic peptide hemagglutinin518-526 from the influenza virus are also able to drive a CD8+ T cell response in vivo. This work demonstrates the potential of SAGEs to act as a modular scaffold for antigen delivery, capable of inducing and boosting specific and tailored immune responses.

The B subunit of Escherichia coli enterotoxin helps control the in vivo growth of solid tumors expressing the Epstein-Barr virus latent membrane protein 2A.

Latent membrane protein 2A (LMP2A) is expressed on almost all Epstein-Barr virus (EBV)-associated tumors and is a potential target for immunotherapeutic intervention and vaccination. However, LMP2A is not efficiently processed and presented on major histocompatibility antigens class I molecules to generate potent cytotoxic T-lymphocytes (CTL) responses capable of killing these tumors. The B subunit of Escherichia coli enterotoxin (EtxB), causes rapid internalization and processing of membrane-bound LMP2A on EBV-infected B cells, and facilitates loading of processed-LMP2A peptides onto MHC class I. This re-directed trafficking/delivery of LMP2A to the MHC class I machinery enhances recognition and killing by LMP2A-specific CTL in vitro. To test the potential of EtxB to enhance immune targeting of LMP2A expressed in solid tumors, we generated a murine tumor model (Renca-LMP2A), in which LMP2A is expressed as a transgenic neoantigen on a renal carcinoma (Renca) cell line and forms solid tumors when injected subcutaneously into BALB/c mice. The data show that in BALB/c mice which have only low levels of peripheral K(d)-LMP2A-specific CD8(+) T cells, merely a transient inhibition of tumor growth is achieved compared with naïve mice; suggesting that there is suboptimal LMP2A-specifc CTL recognition and poorly targeted tumor killing. However, importantly, treatment of these mice with EtxB led to a significant delay in the onset of tumor growth and significantly lower tumor volumes compared with similar mice that did not receive EtxB. Moreover, this remarkable effect of EtxB was achieved despite progressive reduction in tumor expression of LMP2A and MHC class I molecules. These data clearly demonstrate the potential efficacy of EtxB as a novel therapeutic agent that could render EBV-associated tumors susceptible to immune control.

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.

A universal polysaccharide conjugated vaccine against O111 E. coli.

E. coli O111 strains are responsible for outbreaks of blood diarrhea and hemolytic uremic syndrome throughout the world. Because of their phenotypic variability, the development of a vaccine against these strains which targets an antigen that is common to all of them is quite a challenge. Previous results have indicated, however, that O111 LPS is such a candidate, but its toxicity makes LPS forbidden for human use. To overcome this problem, O111 polysaccharides were conjugated either to cytochrome C or to EtxB (a recombinant B subunit of LT) as carrier proteins. The O111-cytochrome C conjugate was incorporated in silica SBA-15 nanoparticles and administered subcutaneously in rabbits, while the O111-EtxB conjugate was incorporated in Vaxcine(TM), an oil-based delivery system, and administered orally in mice. The results showed that one year post-vaccination, the conjugate incorporated in silica SBA-15 generated antibodies in rabbits able to inhibit the adhesion of all categories of O111 E. coli to epithelial cells. Importantly, mice immunized orally with the O111-EtxB conjugate in Vaxcine(TM) generated systemic and mucosal humoral responses against all categories of O111 E. coli as well as antibodies able to inhibit the toxic effect of LT in vitro. In summary, the results obtained by using 2 different approaches indicate that a vaccine that targets the O111 antigen has the potential to prevent diarrhea induced by O111 E. coli strains regardless their mechanism of virulence. They also suggest that a conjugated vaccine that uses EtxB as a carrier protein has potential to combat diarrhea induced by ETEC.

Moraxella catarrhalis adhesin UspA1-derived recombinant fragment rD-7 induces monocyte differentiation to CD14+CD206+ phenotype.

Circulating monocytes in the bloodstream typically migrate to other tissues and differentiate into tissue resident macrophages, the process being determined by the constituents of the microenvironments encountered. These may include microbes and their products. In this study, we investigated whether Moraxella catarrhalis Ubiquitous Surface Protein A1 (UspA1), known to bind to a widely expressed human cell surface receptor CEACAM1, influences monocyte differentiation as receptor engagement has been shown to have profound effects on monocytes. We used the recombinant molecules corresponding to the regions of UspA1 which either bind (rD-7; UspA1527-665) or do not bind (r6-8; UspA1659-863) to CEACAM1 and investigated their effects on CD206, CD80 and CD86 expression on freshly isolated human CD14+ monocytes from peripheral blood mononuclear cells (PBMC). Exposure to rD-7, but not r6-8, biased monocyte differentiation towards a CD14+CD206+ phenotype, with reduced CD80 expression. Monocytes treated with rD-7 also secreted high levels of IL-1ra and chemokine IL-8 but not IL-10 or IL-12p70. The effects of rD-7 were independent of any residual endotoxin. Unexpectedly, these effects of rD-7 were also independent of its ability to bind to CEACAM1, as monocyte pre-treatment with the anti-CEACAM antibody A0115 known to inhibit rD-7 binding to the receptor, did not affect rD-7-driven differentiation. Further, another control protein rD-7/D (a mutant form of rD-7, known not to bind to CEACAMs), also behaved as the parent molecule. Our data suggest that specific regions of M. catarrhalis adhesin UspA1 may modulate inflammation during infection through a yet unknown receptor on monocytes.

Human tonsil-derived dendritic cells are poor inducers of T cell immunity to mucosally encountered pathogens.

The mucosal immune system must initiate and regulate protective immunity, while balancing this immunity with tolerance to harmless antigens and bacterial commensals. We have explored the hypothesis that mucosal dendritic cells (DC) control the balance between regulation and immunity, by studying the responses of human tonsil-derived DC to Neisseria meningitidis as a model organism. We show that tonsil DC are able to sample their antigenic environment, internalizing Nm and expressing high levels of HLA-DR and CD86. However, in comparison to monocyte-derived DC (moDC), they respond to pathogen encounter with only low level cytokine production, largely dominated by TGFß. Functionally, tonsil DC also only stimulated low levels of antigen-specific T cell proliferation and cytokine production when compared to moDC. We therefore propose that the default role for DC in the nasopharynx is to maintain tolerance/ignorance of the large volume of harmless antigens and bacterial commensals encountered at the nasopharyngeal mucosa.

Polysaccharide-specific memory B cells generated by conjugate vaccines in humans conform to the CD27+IgG+ isotype-switched memory B Cell phenotype and require contact-dependent signals from bystander T cells activated by bacterial proteins to differentiate into plasma cells.

The polysaccharides (PS) surrounding encapsulated bacteria are generally unable to activate T cells and hence do not induce B cell memory (BMEM). PS conjugate vaccines recruit CD4(+) T cells via a carrier protein, such as tetanus toxoid (TT), resulting in the induction of PS-specific BMEM. However, the requirement for T cells in the subsequent activation of the BMEM at the time of bacterial encounter is poorly understood, despite having critical implications for protection. We demonstrate that the PS-specific BMEM induced in humans by a meningococcal serogroup C PS (Men C)-TT conjugate vaccine conform to the isotype-switched (IgG(+)CD27(+)) rather than the IgM memory (IgM(+)CD27(+)) phenotype. Both Men C and TT-specific BMEM require CD4(+) T cells to differentiate into plasma cells. However, noncognate bystander T cells provide such signals to PS-specific BMEM with comparable effect to the cognate T cells available to TT-specific BMEM. The interaction between the two populations is contact-dependent and is mediated in part through CD40. Meningococci drive the differentiation of the Men C-specific BMEM through the activation of bystander T cells by bacterial proteins, although these signals are enhanced by T cell-independent innate signals. An effect of the TT-specific T cells activated by the vaccine on unrelated BMEM in vivo is also demonstrated. These data highlight that any protection conferred by PS-specific BMEM at the time of bacterial encounter will depend on the effectiveness with which bacterial proteins are able to activate bystander T cells. Priming for T cell memory against bacterial proteins through their inclusion in vaccine preparations must continue to be pursued.

Impairment of pneumococcal antigen specific isotype-switched Igg memory B-cell immunity in HIV infected Malawian adults.

Pneumococcal disease is associated with a particularly high morbidity and mortality amongst adults in HIV endemic countries. Our previous findings implicating a B-cell defect in HIV-infected children from the same population led us to comprehensively characterize B-cell subsets in minimally symptomatic HIV-infected Malawian adults and investigate the isotype-switched IgG memory B-cell immune response to the pneumococcus. We show that similar to vertically acquired HIV-infected Malawian children, horizontally acquired HIV infection in these adults is associated with IgM memory B-cell (CD19(+) CD27(+) IgM(+) IgD(+)) depletion, B-cell activation and impairment of specific IgG B-cell memory to a range of pneumococcal proteins. Our data suggest that HIV infection affects both T-cell independent and T-cell dependent B-cell maturation, potentially leading to impairment of humoral responses to extracellular pathogens such as the pneumococcus, and thus leaving this population susceptible to invasive disease.

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.

Naturally-acquired influenza-specific CD4+ T-cell proliferative responses are impaired in HIV-infected African adults.

BACKGROUND: Seasonal influenza has been associated with greater morbidity and mortality in AIDS patients. Highly-active antiretroviral therapy (HAART) has led to some reduction in influenza-related complications but the nature of naturally-acquired T-cell immunity to influenza virus in an African setting, and how this changes with immune reconstitution following HAART is unknown. We measured influenza-specific CD4(+) T-cell immunity in unimmunized HIV-infected Malawian adults and then investigated immune reconstitution following HAART. METHODS: Peripheral blood mononuclear cells were isolated from HIV-infected and HIV-uninfected Malawian adults. CFSE proliferation and CD154 expression flow cytometry-based assays were used to measure influenza-specific CD4(+) T-cell immunity. RESULTS: We found lower naturally-acquired proliferative influenza-specific CD4(+) T-cell responses in AIDS patients that was also present in asymptomatic HIV-infected adults with relatively high CD4 counts (>350 cells/µl). Influenza-specific CD4(+) T-cell immune reconstitution in HIV-infected patients on HAART for 12 months was poor despite a marked reduction in viral load and an increase in CD4 count. This poor immune reconstitution was characterised by a low influenza-specific proliferative CD4(+) T-cell response and reduced proportions of CD154-expressing influenza-specific CD4(+) T-cells in peripheral blood. CONCLUSION: Our data suggest that asymptomatic HIV-infected adults may also be at risk of influenza-related complications and that HAART alone may not circumvent this risk in AIDS patients. This study highlights the need to identify possible interventions early in HIV infection to reduce the risk of influenza and to intensify influenza surveillance in these susceptible African populations.

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.

Do multiple concurrent infections in African children cause irreversible immunological damage?

Much of the developing world, particularly sub-Saharan Africa, has high levels of morbidity and mortality associated with infectious diseases. The greatest risk of invasive disease is in the young, the malnourished and HIV-infected individuals. In many regions in Africa these vulnerable groups and the wider general population are under constant immune pressure from a range of environmental factors, under-nutrition and multiple concurrent infections from birth through to adulthood. Intermittent microbial exposure during childhood is required for the generation of naturally acquired immunity capable of protection against a range of infectious diseases in adult life. However, in the context of a resource-poor setting, the heavy burden of malarial, diarrhoeal and respiratory infections in childhood may subvert or suppress immune responses rather than protect, resulting in sub-optimal immunity. This review will explore how poor maternal health, HIV exposure, socio-economic and seasonal factors conspire to weaken childhood immune defences to disease and discuss the hypothesis that recurrent infections may drive immune dysregulation, leading to relative immune senescence and premature immunological aging.

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

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

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.

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.

Mucosal immunity in resource-limited setting: is the battle ground different?

In many developing countries, populations are under considerable pressure from high bacterial exposure on mucosal surfaces. Immune dysregulation in this setting is multifactorial and is driven by a range of environmental factors, undernutrition and coinfections such as measles, malaria and HIV. Disruption or subversion of respiratory-tract and intestinal epithelial barriers leads to increased invasion by mucosal pathogens and a high frequency of life-threatening bacterial disease. It is our opinion that a process of epithelial barrier dysfunction and immune dysregulation at these mucosal surfaces leads to the much higher rates of pneumonia, meningitis and severe sepsis seen in resource-limited countries.

Neisseria lactamica selectively induces mitogenic proliferation of the naive B cell pool via cell surface Ig.

Neisseria lactamica is a commensal bacteria that colonizes the human upper respiratory tract mucosa during early childhood. In contrast to the closely related opportunistic pathogen Neisseria meningitidis, there is an absence of adaptive cell-mediated immunity to N. lactamica during the peak age of carriage. Instead, outer membrane vesicles derived from N. lactamica mediate a B cell-dependent proliferative response in mucosal mononuclear cells that is associated with the production of polyclonal IgM. We demonstrate in this study that this is a mitogenic human B cell response that occurs independently of T cell help and any other accessory cell population. The ability to drive B cell proliferation is a highly conserved property and is present in N. lactamica strains derived from diverse clonal complexes. CFSE staining of purified human tonsillar B cells demonstrated that naive IgD(+) and CD27(-) B cells are selectively induced to proliferate by outer membrane vesicles, including the innate CD5(+) subset. Neither purified lipooligosaccharide nor PorB from N. lactamica is likely to be responsible for this activity. Prior treatment of B cells with pronase to remove cell-surface Ig or treatment with BCR-specific Abs abrogated the proliferative response to N. lactamica outer membrane vesicles, suggesting that this mitogenic response is dependent upon the BCR.

A comparative evaluation of fluoridated and non-fluoridated mouthrinses using a 5-day cycling enamel erosion model.

OBJECTIVES: To assess the relative protective effect of commercial mouthrinses containing 0-450 ppm fluoride on erosion progression in enamel using a simulated 5-day in vitro cycling model with concurrent monitoring of surface microhardness (SMH) and bulk tissue loss. METHODS: Specimens were randomly assigned to six treatment groups (n=6). The model mimicked morning and evening use with rinse times (30 or 60 s) reflecting those prescribed on pack, interspersed with three cycles of demineralisation/remineralisation per simulated day. The latter comprised 1.0% citric acid monohydrate pH 3.2 for 300 s, with subsequent remineralisation in mucin-free artificial saliva pH7.0 for 120 min. SMH was determined by Vickers microindentation and bulk tissue loss using white-light interferometry. RESULTS: From the end of day 1, fluoride-containing mouthrinses conferred statistically significant reductions in bulk tissue loss versus fluoride-free rinses (p<0.05), with lesion depth inversely proportional to fluoride concentration. From day 3, the mean lesion depth of specimens treated with the 450 ppm rinse were statistically significantly lower than all comparator treatment groups (p<0.05). Two distinct trends were apparent when comparing SMH changes in groups treated with fluoride-free versus fluoride-containing mouthrinses. In the latter, SMH levelled out over the final three simulated days in contrast to the former whose SMH continued to fall; differences were statistically significant at day 5 (p< 0.05). CONCLUSIONS: Bulk tissue loss is inversely proportional to fluoride concentration in this cycling model. The plateau in SMH reflects stabilisation of mineral density as the study progresses and the number of fluoride binding sites and consequently uptake increases, in turn leading to enhanced lesion remineralisation.

T cell memory response to pneumococcal protein antigens in an area of high pneumococcal carriage and disease.

BACKGROUND: Streptococcus pneumoniae is a leading cause of vaccine-preventable disease worldwide. Pneumococcal protein antigens are currently under study as components of potential vaccines that offer protection against multiple serotypes. We have therefore characterized T cell pneumococcal immunity acquired through asymptomatic carriage. METHODS: Peripheral blood mononuclear cells from 40 healthy Gambian adults were stimulated with supernatants derived from S. pneumoniae strain (D39), 2 isogenic mutant strains lacking either pneumolysin or choline binding protein A, and recombinant pneumolysin. Immune responses were measured by cellular proliferation and by interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot and bioplex cytokine assays. Nasopharyngeal swabs were cultured to determine carriage rates. RESULTS: S. pneumoniae nasopharyngeal carriage was detected in 60% of individuals. Both effector and resting (or central) CD4(+) T cell memory were frequently present to a range of pneumococcal antigens. However, the level of the effector memory response did not relate to current nasopharyngeal carriage. Pneumolysin was not immunodominant in these T cell responses but induced a distinct proinflammatory profile (high IFN-gamma, IL-12[p40], and L-17 levels and low IL-10 and IL-13 levels). CONCLUSIONS: In this population, T cell-mediated immunological memory potentially capable of pathogen clearance and immune surveillance is common but is not associated with the absolute interruption of pneumococcal carriage. How this naturally acquired immune memory influences pneumococcal vaccine efficacy remains to be determined.