The human antibody response to pneumococcal capsular polysaccharides is dependent on the CD40-CD40 ligand interaction

Complementary Role of CD4+ T Cells in Response to Pneumococcal Polysaccharide Vaccines in Humans

Bacterial pathogens expressing capsular polysaccharides are common causes of mucosal infections (pneumonia, intestinal), as well as often fatal, invasive infections (meningitis, bloodstream infections) in children and adults worldwide. These chemically simple but structurally complex carbohydrate structures on the bacterial surface confer resistance to recognition and clearance by the immune system through a range of mechanisms. Such recognition of capsular polysaccharides may be reduced by their limited ability to directly stimulate B cells and the T cells that may facilitate these humoral responses. The capsules may promote the evasion of complement deposition and activation and may sterically shield the recognition of other subjacent protein antigens by innate factors. Antibodies to capsular polysaccharides, elicited by infection and vaccines, may overcome these obstacles and facilitate bacterial agglutination at mucosal surfaces, as well as the opsonization and clearance of these organisms in tissues and the systemic compartment. However, the immunogenicity of these antigens may be limited by their lack of direct recognition by T cells (“T-independent” antigens) and their restricted ability to generate effective memory responses. In this review, we consider the mechanisms by which polysaccharides may initiate B cell responses and specific antibody responses and the role of T cells, particularly CD4+ follicular helper (TFH) cells to support this process. In addition, we also consider more recent counterintuitive data that capsular polysaccharides themselves may bind major histocompatibility antigen HLA class II to provide a more physiologic mechanism of T cell enhancement of B cell responses to capsular polysaccharides. Defining the contributions of T cells in the generation of effective humoral responses to the capsular polysaccharides will have important implications for understanding and translating this immunobiology for the development of more effective vaccines, to prevent the morbidity and mortality associated with these common mucosal and invasive pathogens in populations at risk.

Production of IgG antibodies to pneumococcal polysaccharides is associated with expansion of ICOS+ circulating memory T follicular-helper cells which is impaired by HIV infection

Dysfunction of T follicular-helper (T_FH) cells is a possible cause of impaired germinal centre (GC) and IgG antibody responses in individuals with human immunodeficiency virus-1 (HIV-1) infection and might contribute to decreased magnitude and isotype diversification of IgG antibodies to pneumococcal polysaccharides (PcPs). We examined the production of IgG1 and IgG2 antibodies to PcPs 4, 6B, 9V and 14 by enumerating antibody secreting cells (ASCs) at day (D) 7 and determining fold-increase in serum antibody levels at D28 after vaccination with unconjugated PcPs in HIV seronegative subjects (n = 20) and in HIV patients who were receiving antiretroviral therapy (ART) (n = 28) or who were ART-naive (n = 11) and determined their association with ICOS⁺ and ICOS^- circulating memory T_FH (cmT_FH) cells (CD4⁺CD45RA^-CD27⁺CXCR5⁺PD-1⁺) and short lived plasmablasts (SPBs) at D7, and with PcP-specific and total IgM⁺ and IgG⁺ memory B cells at D0. In HIV seronegative subjects, production of IgG1⁺ and IgG2⁺ ASCs was consistently associated with the frequency of ICOS⁺ cmT_FH cells but not ICOS^- cmT_FH cells or memory B cells. In contrast, post-vaccination ASCs in HIV patients, regardless of ART status, were lower than in HIV seronegative subjects and not associated with ICOS⁺ cmT_FH cells, the expansion of which was absent (ART-naive patients) or much lower than in HIV seronegative subjects (ART-treated patients). Production of SPBs was also lower in ART-naive patients. Fold-increase in IgG2 antibodies at D28 also correlated with ICOS⁺ cmT_FH cells at D7 in HIV seronegative subjects but not in HIV patients. These novel findings provide evidence that ICOS⁺ cmT_FH cells contribute to the regulation of PcP-specific IgG antibody responses, including isotype diversification, and that T_FH cell dysfunction may be a cause of impaired PcP-specific IgG antibody responses and increased susceptibility to pneumococcal disease in HIV patients.

Identifying host genetic risk factors in the context of public health surveillance for invasive pneumococcal disease

Host genetic factors that modify risk of pneumococcal disease may help target future public health interventions to individuals at highest risk of disease. We linked data from population-based surveillance for invasive pneumococcal disease (IPD) with state-based newborn dried bloodspot repositories to identify biological samples from individuals who developed invasive pneumococcal disease. Genomic DNA was extracted from 366 case and 732 anonymous control samples. TagSNPs were selected in 34 candidate genes thought to be associated with host response to invasive pneumococcal disease, and a total of 326 variants were successfully genotyped. Among 543 European Americans (EA) (182 cases and 361 controls), and 166 African Americans (AA) (53 cases and 113 controls), common variants in surfactant protein D (SFTPD) are consistently underrepresented in IPD. SFTPD variants with the strongest association for IPD are intronic rs17886286 (allelic OR 0.45, 95% confidence interval (CI) [0.25, 0.82], with p = 0.007) in EA and 5' flanking rs12219080 (allelic OR 0.32, 95%CI [0.13, 0.78], with p = 0.009) in AA. Variants in CD46 and IL1R1 are also associated with IPD in both EA and AA, but with effects in different directions; FAS, IL1B, IL4, IL10, IL12B, SFTPA1, SFTPB, and PTAFR variants are associated (p≤0.05) with IPD in EA or AA. We conclude that variants in SFTPD may protect against IPD in EA and AA and genetic variation in other host response pathways may also contribute to risk of IPD. While our associations are not corrected for multiple comparisons and therefore must be replicated in additional cohorts, this pilot study underscores the feasibility of integrating public health surveillance with existing, prospectively collected, newborn dried blood spot repositories to identify host genetic factors associated with infectious diseases.

Immune response to pneumococcal polysaccharide vaccine in adults with chronic plaque psoriasis treated with alefacept

BACKGROUND

Alefacept is a T cell-modulating biologic therapy for psoriasis that could affect patients' ability to mount immune responses.

OBJECTIVE

This open-label, phase IV, multicenter study assessed the ability of adults with chronic plaque psoriasis receiving alefacept to generate antibodies to a pneumococcal polysaccharide vaccine (PPV).

METHODS

Patients were treated with a standard 12-week course of alefacept and administered the 23-valent PPV at week 6. Antipneumococcal antibodies were measured at baseline and weeks 6, 9, 12, and 33. The primary end point was the percentage of patients with a 2-fold or greater increase from prevaccination (week 6) to 6 weeks postvaccination (week 12) in antibody titers to 2 or more of 5 designated PPV antigens.

RESULTS

Of 43 patients enrolled, 42 were included in the full analysis set, with 86% of patients exhibiting a 2-fold or greater increase and 57% of patients exhibiting a 4-fold or greater increase in antibody titers to 2 or more of 5 designated antigens from prevaccination to 6 weeks postvaccination. At 6 months postvaccination, 78% of patients had a 2-fold or greater increase and 47% of patients had a 4-fold or greater increase in antibody titers to 2 or more of the 5 designated antigens. There were statistically significant increases in mean antibody titers to all 23 antigens in PPV from prevaccination to 6 weeks postvaccination.

LIMITATIONS

This was an open-label study with no comparator.

CONCLUSIONS

Most patients mounted immune responses to PPV; increases in antibody titers in these patients were consistent with those seen in healthy individuals.

Selective defect of anti-pneumococcal IgG in a patient with persistent polyclonal B cell lymphocytosis

BACKGROUND

Persistent polyclonal B cell lymphocytosis (PPBL) is a rare condition characterized by increased IgM and large excess of B cells with an IgD(+) CD27(+) phenotype. In normal individuals, these cells play a central role in the defense against pneumococcal infection. So far, few studies have characterized humoral immune responses in PPBL patients. We therefore measured IgG directed against S. pneumoniae antigens in a 51 yr-old woman with PPBL before and after vaccination with a pneumococcal 23-valent polysaccharide vaccine.

METHODS

Antibodies against pneumococcal antigens were measured first with an overall immunoassay using microplates coated with the 23-valent pneumococcal vaccine. A serotype-specific test was also performed according to the WHO consensus protocol.

RESULTS

Despite a large number of IgD(+) CD27(+) cells, our patient had low baseline titers of IgG directed against pneumococcal antigens and did not significantly respond to a 23-valent polysaccharide vaccine against S. pneumoniae. On the contrary, she had good titers of IgG directed against tetanus toxoid.

CONCLUSION

IgM(+) IgD(+) CD27(+) cells which accumulate in this patient with typical PPBL patient failed to perform IgG isotype switch after a polysaccharide vaccine. The potential mechanisms and relationships with the main features of PPBL are discussed. Further studies on a larger number of similar patients are needed.

Generation of antibody responses to pneumococcal capsular polysaccharides is independent of CD1 expression in mice

Streptococcus pneumoniae is a bacterial microorganism that frequently causes serious infection, particularly in children and the elderly. Protection against infection with S. pneumoniae is based mainly on the generation of antibodies to the pneumococcal capsular polysaccharides (caps-PS), but the mechanisms responsible for the generation of anticapsular antibodies remain incompletely understood. The aim of the present study was to evaluate the role of CD1-restricted T cells in the antibody response to caps-PS. When immunized with Pneumo23, wild-type mice and CD1 knockout mice on BALB/c and C57BL/6 backgrounds generated immunoglobulin M (IgM) and IgG antibody responses to soluble caps-PS that were comparable. Similar results were obtained after immunization with heat-inactivated S. pneumoniae. The IgM and IgG antibody response of wild-type mice to Pneumo23 was not affected by an antagonizing monoclonal anti-CD1 antibody treatment. In summary, our data provide evidence that the antibody response to caps-PS is generated independently of CD1 expression.

Vaccination response to tetanus toxoid and 23-valent pneumococcal vaccines following administration of a single dose of abatacept: a randomized, open-label, parallel group study in healthy subjects

The effect of abatacept, a selective T-cell co-stimulation modulator, on vaccination has not been previously investigated. In this open-label, single-dose, randomized, parallel-group, controlled study, the effect of a single 750 mg infusion of abatacept on the antibody response to the intramuscular tetanus toxoid vaccine (primarily a memory response to a T-cell-dependent peptide antigen) and the intramuscular 23-valent pneumococcal vaccine (a less T-cell-dependent response to a polysaccharide antigen) was measured in 80 normal healthy volunteers. Subjects were uniformly randomized to receive one of four treatments: Group A (control group), subjects received vaccines on day 1 only; Group B, subjects received vaccines 2 weeks before abatacept; Group C, subjects received vaccines 2 weeks after abatacept; and Group D, subjects received vaccines 8 weeks after abatacept. Anti-tetanus and anti-pneumococcal (Danish serotypes 2, 6B, 8, 9V, 14, 19F and 23F) antibody titers were measured 14 and 28 days after vaccination. While there were no statistically significant differences between the dosing groups, geometric mean titers following tetanus or pneumococcal vaccination were generally lower in subjects who were vaccinated 2 weeks after receiving abatacept, compared with control subjects. A positive response (defined as a twofold increase in antibody titer from baseline) to tetanus vaccination at 28 days was seen, however, in ≥ 60% of subjects across all treatment groups versus 75% of control subjects. Similarly, over 70% of abatacept-treated subjects versus all control subjects (100%) responded to at least three pneumococcal serotypes, and approximately 25–30% of abatacept-treated subjects versus 45% of control subjects responded to at least six serotypes.

Specific intracellular adhesion molecule-grabbing nonintegrin R1 is not involved in the murine antibody response to pneumococcal polysaccharides

Streptococcus pneumoniae is a microorganism that frequently causes serious infections in children, the elderly, and immunocompromised patients. We studied whether the specific intracellular adhesion molecule-grabbing nonintegrin R1 (Sign-R1) receptor, involved in the uptake of capsular polysaccharides (caps-PS) by antigen-presenting cells, is necessary for the antibody response to pneumococcal caps-PS and phosphorylcholine (PC). The antibody response to caps-PS and PC was evaluated after vaccination with soluble caps-PS (Pneumovax) and after vaccination with heat-killed S. pneumoniae. The role of Sign-R1 was investigated by using Sign-R1 knockout mice and anti-Sign-R1 monoclonal antibodies. The immunoglobulin M (IgM) and IgG antibody response to PC and caps-PS (serotypes 3 and 14) was not affected by anti-Sign-R1 monoclonal antibodies. The IgM antibody response in Sign-R1 knockout mice was comparable to the antibody response in wild-type mice. The IgG antibody response to serotype 3, but not to serotype 14, tended to be lower in Sign-R1 knockout mice compared to wild-type mice. In conclusion, we found that Sign-R1 is not involved in the IgM antibody production to PC and caps-PS serotype 3 or 14 and the IgG immune response to PC and caps-PS serotype 14. There is no direct relation between capture and uptake of caps-PS serotype 14 by Sign-R1 and the initiation of the anti-caps-PS antibody production in mice.

Active vaccination in patients with common variable immunodeficiency (CVID)

Active vaccination of CVID patients with standard vaccines has rarely been studied in depth although some patients have been shown to develop transient vaccine-specific immunity. We addressed the question whether these patients can be identified by functional classification of their B cell subsets in vitro. Twenty-one CVID patients receiving regular IgG substitution were immunized with anti-peptide and anti-polysaccharide vaccines. Humoral vaccination responses were compared to the numbers of circulating memory B cells, CD21(low) B cells and the capacity to produce antibodies in vitro. Our findings allow four conclusions: (1) positive vaccination responses are not contradictory to the diagnosis of CVID; they occurred against polypeptide vaccines in 23% and against polysaccharide antigens in 18% of all vaccinations. (2) Class-switched antibody responses occur preferentially in patients of CVID group II. (3) A normal percentage of IgM memory B cells is necessary but not sufficient for a vaccination response to polysaccharide antigens. (4) Active vaccination in addition to IgG replacement therapy should be performed in patients of CVID type II - especially in case of vaccines for which passive protection cannot be guaranteed.

Chronic Chlamydia pneumoniae infection may promote coronary artery disease in humans through enhancing secretion of interleukin-4

Atherosclerosis is an inflammatory response, probably to a range of initiating causes. Chronic infection with Chlamydia pneumoniae (C.pn) has been suggested as one cause, but the nature of the association is controversial, in large part due to lack of an identified mechanism to link infection with the atherosclerotic process in man. This study examined 139 consecutive subjects with stable chest pain, with the aim of correlating the serological status of C.pn infection with the pattern of secretion of cytokines from CD4(+) T lymphocytes. C.pn seropositive subjects secreted significantly more interleukin (IL)-4 than did those who were C.pn seronegative (P = 0.02). No significant difference was noted for secreted interferon (IFN)-gamma. The amount of secreted IL-4, but not of secreted IFN-gamma, correlated positively with the extent of coronary artery disease (P = 0.006). A similar correlation with secreted IL-4 was not identified with Helicobacter pylori infection. These results support the hypothesis that C.pn infection contributes to the inflammatory process responsible for coronary artery atherosclerosis. The method used to detect cytokine secretion involves ligation of CD40L on blood CD4(+) T cells, which may have relevance to tissue events.

IRAK4 and NEMO mutations in otherwise healthy children with recurrent invasive pneumococcal disease

BACKGROUND

About 2% of childhood episodes of invasive pneumococcal disease (IPD) are recurrent, and most remain unexplained.

OBJECTIVE

To report two cases of otherwise healthy, unrelated children with recurrent IPD as the only clinical infectious manifestation of an inherited disorder in nuclear factor-kappaB(NF-kappaB)-dependent immunity.

RESULTS

One child carried two germline mutations in IRAK4, and had impaired cellular responses to interleukin (IL)1 receptor and toll-like receptor (TLR) stimulation. The other child carried a hemizygous mutation in NEMO, associated with a broader impairment of NF-kappaB activation, with an impaired cellular response to IL-1R, TLR and tumour necrosis factor receptor stimulation. The two patients shared a narrow clinical phenotype, associated with two related but different genotypes.

CONCLUSIONS

Otherwise healthy children with recurrent IPD should be explored for underlying primary immunodeficiencies affecting the IRAK4-dependent and NEMO-dependent signalling pathways.

CD4+ T Lymphocytes Expressing CD40 Ligand Help the IgM Antibody Response to Soluble Pneumococcal Polysaccharides via an Intermediate Cell Type

Streptococcus pneumoniae causes serious infections in children, the elderly, and immunocompromised patients. Protection against infections with S. pneumoniae is mediated through Abs against the capsular polysaccharides (caps-PS). We previously showed that the murine Ab response to caps-PS is dependent on CD40-CD40L interaction. In the present paper, we addressed the question of whether the CD40-CD40L-mediated modulation of the anti-caps-PS immune reaction is the result of a direct interaction between B lymphocytes and T lymphocytes or of an indirect interaction. SCID/SCID mice reconstituted with B lymphocytes from wild-type mice did not mount anti-caps-PS Abs. SCID/SCID mice reconstituted with B lymphocytes from wild-type mice and CD4+ T lymphocytes from wild-type mice but not CD4+ T lymphocytes from CD40L knockout mice stimulated the anti-caps-PS Ab response. This indicated that CD4+ T lymphocytes stimulated the anti-caps-PS Ab response in a CD40L-dependent manner. SCID/SCID mice reconstituted with B lymphocytes from CD40 knockout mice and CD4+ T lymphocytes from wild-type mice generated an anti-caps-PS Ab response that could be inhibited by MR1, a blocking anti-CD40L Ab. These data indicated that CD4+ T lymphocytes stimulated the anti-caps-PS Ab response in an indirect way. Finally, lethally irradiated CD40 knockout mice reconstituted with bone marrow from wild-type mice mounted an anti-caps-PS Ab response that was comparable to the Ab response in wild-type mice, revealing that the required CD40 was on hemopoietic cells. In conclusion, we provide evidence that CD4+ T lymphocytes expressing CD40L stimulate the Ab response to soluble caps-PS by interacting with CD40-expressing non-B cells.

Inhalative vaccination with pneumococcal polysaccharide in healthy volunteers

In order to determine the feasibility of inhalative vaccination with polysaccharide antigen, we used controlled inhalation of a defined dose of Pneumovax in a randomized 3-arm study. The vaccine was either deposited in the alveoli (alveolar vaccination) or in the large airways (bronchial vaccination) and this was compared to standard intra-muscular vaccination. Adverse effects were minor and never exceeded WHO grade 2. There was frequent cough in the inhalative groups and frequent local pain at the injection site in the intra-muscular group. Specific serum IgG antibody measured before, and 4 and 12 weeks after, vaccination showed a greater than 2-fold rise in 4 out of 10 individuals after alveolar vaccination and in 6 out of 10 individuals after bronchial vaccination as compared to 10 out of 10 in the intra-muscular vaccination group. Average antibody levels of responders at 12 weeks were 350 microg/ml for alveolar vaccination, 200 microg/ml for bronchial vaccination and 1010 microg/ml for standard intra-muscular vaccination. Analysis of antibodies for 9 specific serotypes showed a more than 3-fold rise to 7-9 of the serotypes in the intra-muscular group. In both the bronchial and the alveolar group, all subjects responded but this was restricted to 2-4 of the 9 serotypes. The data show that polysaccharide vaccine can be safely administered by controlled inhalation and that it can induce good, albeit lower, serum antibody responses.

Blockade of CTLA-4 (CD152) enhances the murine antibody response to pneumococcal capsular polysaccharides

The capsular polysaccharides (caps-PS) of Streptococcus pneumoniae are classified as thymus-independent antigens. Nevertheless, T lymphocytes can modulate the antibody response to caps-PS. In this study, we show that anticytotoxic T lymphocyte-associated antigen 4 (CTLA-4) treatment, along with administration of caps-PS to BALB/c mice, resulted in a dose-dependent generation of a strong caps-PS-specific antibody response. Anti-CTLA-4 treatment had no effect on the immunoglobulin G (IgG) antibody production in athymic nu/nu mice. Anti-CTLA-4 treatment stimulated the IgG antibody production in severe combined immunodeficiency (SCID)/SCID mice reconstituted with CTLA-4(-/-) B lymphocytes and wild-type T lymphocytes. This excluded the possibility that anti-CTLA-4 enhanced antibody production by direct interaction with B lymphocytes. Anti-CTLA-4 treatment enhanced the antibody production in SCID/SCID mice reconstituted with B lymphocytes and CD4(+) and CD8(+) T lymphocytes but not in SCID/SCID mice reconstituted with B lymphocytes in the absence of CD4(+) and/or CD8(+) cells. Administration of anti-CTLA-4 in BALB/c mice but not in nu/nu mice resulted in a markedly increased production of interleukin (IL)-2, IL-4, and interferon-gamma. Taken together, these data strongly suggest a role of T lymphocytes and CTLA-4 in the regulation of the antibody response to caps-PS.

1alpha,25-Dihydroxyvitamin D3 modulates the murine antibody response to pneumococcal capsular polysaccharide serotype 3 through IL-12

1alpha,25-Dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is a steroid hormone that regulates calcium metabolism. Besides, 1alpha,25(OH)(2)D(3 )also has pronounced immunomodulatory effects: it strongly inhibits dendritic cell (DC) maturation and impairs IL-12 production. We studied the effect of 1alpha,25(OH)(2)D(3 )on the antibody response to pneumococcal capsular polysaccharide (caps-PS) serotype 3. 1alpha,25(OH)(2)D(3) inhibited the IgG2a antibody response to caps-PS serotype 3. Besides, 1alpha,25(OH)(2)D(3) also inhibited IL-12 production and maturation of DC. Anti-IL-12 and exogenous IL-12, respectively, inhibited and stimulated the IgG2a antibody response to caps-PS serotype 3. Exogenous IL-12 abrogated the effect of 1alpha,25(OH)(2)D(3) on the IgG2a antibody response to caps-PS serotype 3, indicating that the effect of 1alpha,25(OH)(2)D(3) on the IgG2a antibody response to caps-PS serotype 3 was mediated through IL-12. In conclusion, we demonstrate that 1alpha,25(OH)(2)D(3) has an inhibitory effect on the IgG2a antibody response to caps-PS serotype 3, and that this effect was mediated trough IL-12.