[Proteins of Streptococcus pneumoniae: perspectives for development of pneumococcal vaccine]

Streptococcus pneumoniae cell wall and cytoplasmic proteins contribute directly to pathogenesis of pneumococcal infection. Protective effect of pneumococcal proteins such as pneumolysin (Ply), muramylamidase (LytA) and pneumococcal surface protein A (PspA). There is discussion in the literature about development of conjugared pneumococcal vaccines, which should include polysaccharides of invasive serotypes of pneumococci as well as protein antigens of this pathogen, for prevention of infections caused by S. pneumoniae. Researches suggest that such hybrid vaccines will be effective, first of all, for children < 2 years of age and elderly > 65 years old because immune response to polysaccharide vaccines either do not form at all or insufficient for prevention of pneumococcal infection.

The role of beta-hemolytic streptococci in causing diffuse, nonculturable cellulitis: a prospective investigation

Staphylococcus aureus and beta-hemolytic streptococci (BHS) are the 2 main types of bacteria causing soft-tissue infections. Historically, BHS were believed to be the primary cause of diffuse, nonculturable cellulitis. However, with the recent epidemic of community-associated methicillin-resistant S aureus (MRSA) causing culturable soft-tissue infections, it is currently unclear what role either of these bacteria has in cases where the cellulitis is diffuse and nonculturable. This uncertainty has led to broad-spectrum and haphazard use of antibiotics for this infection type, which has led to increased risk of adverse drug reactions, health care costs, and emergence of resistance in bacteria. To investigate this issue, we conducted a prospective investigation between December 2004 and June 2007, enrolling all adult patients admitted to the inpatient service at the Olive View-UCLA Medical Center, a county hospital of Los Angeles, with diffuse, nonculturable cellulitis. Acute and convalescent serologies for anti-streptolysin-O and anti-DNase-B antibodies were obtained. Patient data were analyzed for response to beta-lactam antibiotics. The primary outcome was the proportion of these cases caused by BHS, as diagnosed by serologies and/or blood cultures, and the secondary outcome was the response rate of patients to beta-lactam antibiotics. Of 248 patients enrolled, 69 were dropped from analysis because of loss to follow-up or exclusion criteria. Of the 179 remaining patients, 73% of nonculturable cellulitis cases were caused by BHS. Analysis of outcomes to beta-lactam antibiotic treatment revealed that patients diagnosed with BHS had a 97% (71/73) response, while those who did not have BHS had a 91% (21/23) response, with an overall response rate of 95.8% (116/121). Results of this large, prospective study show that diffuse, nonculturable cellulitis is still mainly caused by BHS, despite the MRSA epidemic, and that for this infection type, treatment with beta-lactam antibiotics is still effective. A cost-effective, evidence-based algorithm can be useful for the empiric management of uncomplicated soft-tissue infections based on the presence or absence of a culturable source.

Streptolysin S inhibits neutrophil recruitment during the early stages of Streptococcus pyogenes infection

In contrast to infection of superficial tissues, Streptococcus pyogenes infection of deeper tissue can be associated with a significantly diminished inflammatory response, suggesting that this bacterium has the ability to both promote and suppress inflammation. To examine this, we analyzed the behavior of an S. pyogenes mutant deficient in expression of the cytolytic toxin streptolysin S (SLS-) and evaluated events that occur during the first few hours of infection by using several models including injection of zebrafish (adults, larvae, and embryos), a transepithelial polymorphonuclear leukocyte (PMN) migration assay, and two-photon microscopy of mice in vivo. In contrast to wild-type S. pyogenes, the SLS- mutant was associated with the robust recruitment of neutrophils and significantly reduced lethal myositis in adult zebrafish. Similarly, the mutant was attenuated in embryos in its ability to cause lethality. Infection of larva muscle allowed an analysis of inflammation in real time, which revealed that the mutant had recruited PMNs to the infection site. Analysis of transepithelial migration in vitro suggested that SLS inhibited the host cells' production of signals chemotactic for neutrophils, which contrasted with the proinflammatory effect of an unrelated cytolytic toxin, streptolysin O. Using two-photon microscopy of mice in vivo, we showed that the extravasation of neutrophils during infection with SLS- mutant bacteria was significantly accelerated compared to infection with wild-type S. pyogenes. Taken together, these data support a role for SLS in the inhibition of neutrophil recruitment during the early stages of S. pyogenes infection.

Streptococcus pneumoniaeProtein Vaccine Candidates: Properties, Activities and Animal Studies

Streptococcus pneumoniae is a causative agent for community acquired pneumonia, bacteremia, acute otitis media, and meningitis. Recent emergence of multi-drug resistant clinical isolates prompts the need of effective vaccine for the prevention of disease. The licensed polysaccharide-based pneumococcal vaccines only elicit protective antibodies against the infection of serotypes that are included in the vaccine. To broaden the protection, the use of pneumococcal proteins will be a feasible and preferable alternative. This communication provides a review on the biochemical properties of these protein candidates, their immunization results in animal studies, and perspectives on the development of protein-based pneumococcal vaccine.

[Structural homology between streptolysin O (SLO) produced by streptococcus pyogenes and SLO-like protein produced by non-pathogenic streptococci and cross-reactivity of antibody against SLO-like protein to SLO]

Nine clones of non-pathogenic streptococci were isolated from the pharynges of seven healthy subjects, and grown on sheep blood agar plates with a hemolysis or gamma hemolysis, then cultured in LB broth for 16 hrs. Purified streptolysin O (SLO) purchased from Sigma Chemical Co. (Sigma-SLO), SLO antigen as a latex agglutination reagent from A company (A-SLO) and supernatants from four culture media were electrophoresed on 12% SDS-polyacrylamide gel and transferred to PVDF membranes. Immunological analyses of antibodies against SLO in healthy sera and proteins in culture medium demonstrated that healthy sera contained an antibody recognizing Sigma-SLO, A-SLO and a protein of the same size as SLO (SLO-like protein) in culture medium. These findings suggest that healthy subjects develop an antibody directed against SLO-like protein produced by non-pathogenic streptococci, and that this antibody cross-reacts with Sigma-SLO and A-SLO. Using DNA from Streptococcus pyogenes and non-pathogenic streptococci, the SLO gene and SLO-like protein gene were analyzed by direct sequencing with oligonucleotide primers designed to cover no. 74 to approximately 1900 of the SLO gene. There were three different bases resulting in amino acid substitution between the SLO gene and SLO-like protein gene, namely 101Lys (AAA) of SLO to Asn (AAT), 175Met (ATG) to Arg (AGG) and 185Asp (GAT) to Asn (AAT). Remaining 560 residues of 563 amino acids constituting SLO-like protein were homologous to SLO. Non-pathogenic streptococci on the pharynges of healthy subjects produce an SLO-like protein composed of amino acids similar to those of SLO, which induces an antibody against this SLO-like protein in serum. It is likely that an antibody against SLO-like protein in healthy sera cross-reacts with SLO and causes a pseudo-positive reaction on ASO measurement by the latex agglutination method using SLO antigen.

c-di-GMP is an effective immunomodulator and vaccine adjuvant against pneumococcal infection

Cyclic diguanylate (c-di-GMP) is a unique bacterial intracellular signaling molecule capable of stimulating enhanced protective innate immunity against various bacterial infections. The effects of intranasal pretreatment with c-di-GMP, or intraperitoneal coadministration of c-di-GMP with the pneumolysin toxoid (PdB) or pneumococcal surface protein A (PspA) before pneumococcal challenge, were investigated in mice. We found that c-di-GMP had no significant direct short-term effect on the growth rate of Streptococcus pneumoniae either in vitro or in vivo. However, intranasal pretreatment of mice with c-di-GMP resulted in a significant decrease in bacterial load in lungs and blood after serotypes 2 and 3 challenge, and a significant decrease in lung titers after serotype 4 challenge. Potential cellular mediators of these enhanced protective responses were identified in lungs and draining lymph nodes. Intraperitoneal coadministration of c-di-GMP with PdB or PspA before challenge resulted in significantly higher antigen-specific antibody titers and increased survival of mice, compared to that obtained with alum adjuvant. These findings demonstrate that local or systemic c-di-GMP administration stimulates innate and adaptive immunity against invasive pneumococcal disease. We propose that c-di-GMP can be used as an effective broad spectrum immunomodulator and vaccine adjuvant to prevent infectious diseases.

Microarray method for multiplex and serial latex agglutination tests with digital image registration

A microarray analytical system for performing tests of latex agglutination reaction in microformat with digital image registration was developed. The system allows the application of latex microdrops to the surface of the carrier in the form of a regular microarray and mixing of the latex droplets with the individual samples in each droplet of the microarray. The reaction is performed in a total mixture volume of about 1 microl for each of 30 samples simultaneously with video registration and interpretation of the results using a scanning device and specially developed software. The results of the semi-quantitative determination of C-Reactive Protein, Rheumatoid Factor and Anti-Streptolysin O concentrations by traditional macro- and proposed micro-arrayagglutination method were compared with the immunoturbidimetric measurements used as reference method. It was concluded that the suggested method for performing latex agglutination reactions on the basis of a microarray approach with digital image evaluation of results can provide a high throughput and reliable results and also offers significant advantages to the traditional latex agglutination tests with visual interpretation. Comprehensive documentation and objectification of readouts show a siginificant improvement to the present methodology.

A pivotal role for pneumolysin in the immunopathogenesis, treatment and prevention of pneumococcal disease

The pneumococcus remains an extremely important cause of morbidity and mortality worldwide. While the microorganism has a number of significant virulence mechanisms, many recent studies have focused on pneumolysin, which is recognised to be one of the most important virulence factors of the organism. The purpose of this manuscript is to review recent developments with respect to the role of pneumolysin in pneumococcal disease. It describes how the cytotoxic and other pro-inflammatory activities of this toxin contribute to disease pathogenesis and pathology, as well as various immunological and pharmacological strategies that may target these deleterious effects of the toxin.

Oriented immobilisation of anti-pneumolysin Fab through a histidine tag for electrochemical immunosensors

Orientation of reagents is a key step in the construction of immunosensors. When the immunoreagent is a recombinant protein, this can be achieved by employing hexahistidine tags. The orientation of recombinant histidine-tagged Fab fragments of monoclonal anti-pneumolysin antibodies on gold films is evaluated. Using histidine as a chelator of Ni or employing an anti-polyhistidine antibody for capturing the His6 residue is considered. Measurements are based in the signal of indigo, which comes from the hydrolysis of 3-indoxylphosphate by alkaline phosphatase (AP). The attachment of the enzyme occurs through the interaction of biotin with AP-labelled streptavidin or employing AP-conjugated immunoreagents. In the case of the interaction Ni-histidine, for the study of the self-assembling process a His-tagged and biotinylated protein (His6-GST-B) was employed. General conditions were studied and non-specific adsorption was avoided with the use of 1-hexanethiol. Improvements of the signal compared with the direct adsorption were only achieved by the use of histidine capturing antibodies. With an optimised ratio anti-polyhis:His6-Fab the signal increases approximately a 100%. Precision is adequate and the response is linear with the concentration of pneumolysin between 0.1 and 10 ng/mL.

Toll-like receptor 2 contributes to antibacterial defence against pneumolysin-deficient pneumococci

Toll-like receptors (TLRs) are pattern recognition receptors that recognize conserved molecular patterns expressed by pathogens. Pneumolysin, an intracellular toxin found in all Streptococcus pneumoniae clinical isolates, is an important virulence factor of the pneumococcus that is recognized by TLR4. Although TLR2 is considered the most important receptor for Gram-positive bacteria, our laboratory previously could not demonstrate a decisive role for TLR2 in host defence against pneumonia caused by a serotype 3 S. pneumoniae. Here we tested the hypothesis that in the absence of TLR2, S. pneumoniae can still be sensed by the immune system through an interaction between pneumolysin and TLR4. C57BL/6 wild-type (WT) and TLR2 knockout (KO) mice were intranasally infected with either WT S. pneumoniae D39 (serotype 2) or the isogenic pneumolysin-deficient S. pneumoniae strain D39 PLN. TLR2 did not contribute to antibacterial defence against WT S. pneumoniae D39. In contrast, pneumolysin-deficient S. pneumoniae only grew in lungs of TLR2 KO mice. TLR2 KO mice displayed a strongly reduced early inflammatory response in their lungs during pneumonia caused by both pneumolysin-producing and pneumolysin-deficient pneumococci. These data suggest that pneumolysin-induced TLR4 signalling can compensate for TLR2 deficiency during respiratory tract infection with S. pneumoniae.

Evidence-based correlation between anti-streptolysin O serum titer and sacroiliac joint disorder

OBJECTIVE

Poststreptococcal reactive arthritis (PSReA) is a nonsuppurative sequela of antecedent streptococcal infection, and can be investigated when detecting the anti-streptolysin O (ASO) titer. The relationship between ASO titer and involvement of the peripheral synovial joints has been examined in PSRA, but data are sparse for the sacroiliac (SI) joint. Quantitative SI joint scintigraphy has been used clinically to detect active SI joint disorders, but not for PSReA.

METHODS

A total of 84 subjects were recruited; mean age at enrollment was 23 years (range 18.0-36.4 yrs). All subjects were examined for ASO titer levels (range 25-520 IU/ml) and SI joint imaging, determined by sacroiliac to sacrum (SI/S) ratio derived from SI scintigraphy.

RESULTS

Most of the subjects with high ASO titer had unclassified or undifferentiated arthritis. Good correlation between the ASO titer and the SI/S ratio was determined statistically using Pearson correlation coefficients. The relationships between ASO titer and SI/S ratio at various locations (laterality: left, right; location of part: upper, middle, lower) were found to be significantly correlated using generalized estimating equations. After adjustment for potential confounders, a highly significant association was determined between ASO titer and SI/S ratio (p < 0.0001), with an increase of 1 IU/ml of titer resulting in a significant increase in SI/S ratio by 0.0008 units. Age was significantly associated with SI/S ratio (p = 0.0022), with each extra year increasing the ratio by 0.0074.

CONCLUSION

Our findings demonstrate a high correlation between SI joint involvement and high ASO titers. Subjects with SI joint involvement should be advised to have an ASO titer examination and quantitative SI joint scintigraphy.

Bacterial superantigens and T cell receptor beta-chain-bearing T cells in the immunopathogenesis of ulcerative colitis

Ulcerative colitis (UC) is a chronic relapsing-remitting inflammatory bowel disease (IBD) that affects the colon and the rectum producing debilitating symptoms, which impair ability to function and quality of life. The aetiology of IBD is incompletely understood, but within the lymphocyte population, specific T cell subsets are known to be major factors in the development of intestinal immune pathology while different subsets are essential regulators, controlling IBD. Hence, IBD is thought to reflect dysregulated T cell behaviour. This study was to investigate if the normal molecular configuration of the T cell receptor (TCR) repertoire is compromised in patients with UC. The percentage of T cell-bearing beta-chain 4 (TCRBV4) was high in patients with UC, and T cells showed polyclonal expansion in the presence of bacterial superantigens (SA) such as streptococcal mitogenic exotoxin Z-2 (SMEZ-2), indicating that bacterial SA promote specific TCRBV family expansion. Further, in patients with UC, the duration of UC was significantly longer in patients with skewed TCRBV4 compared with patients without TCRBV4 skewing, suggesting that long-term exposure to bacterial SA such as SMEZ-2 might promote systemic immune disorders like the remission-relapsing cycles seen in patients with UC. In conclusion, our observations in this study support the perception that the systemic activation of T cells by enteric bacterial SA might lead to a dysregulated, but exuberant immune activity causing the remission and flare-up cycle of mucosal inflammation in patients with UC. Future studies should strengthen our findings and increase understanding on the aetiology of IBD.

Low CD4 T Cell Immunity to Pneumolysin Is Associated with Nasopharyngeal Carriage of Pneumococci in Children

BACKGROUND

Recent studies in mice have suggested that T cell immunity may be protective against pneumococcal infection.

METHODS

CD4 T cell proliferative responses to the pneumococcal proteins pneumolysin (Ply), Ply toxoid (F433), and choline-binding protein A were investigated in peripheral blood mononuclear cells (PBMCs) and adenoidal mononuclear cells (MNCs) obtained from children undergoing adenoidectomy.

RESULTS

Ply and F433 induce significant proliferation of CD4 T cells in both PBMCs and adenoidal MNCs, and both memory and naive phenotypes of CD4 T cells proliferated after stimulation. In PBMCs, CD4 T cell proliferation induced by Ply and F433, which was associated with increased production of interferon (IFN)- gamma and tumor necrosis factor (TNF)- alpha , was significantly lower in children who were culture positive for pneumococcus than in those who were culture negative for pneumococcus (P<.05). Between groups, no such difference was observed in adenoidal MNC CD4 T cell proliferation, which was associated with production of IFN- gamma and interleukin (IL)-10. The CD4 T cell proliferation induced by Ply and F433 was inhibited by antibodies to Toll-like receptor 4.

CONCLUSION

These data suggest that Ply induces CD4 T cell proliferative responses with production of IFN- gamma and TNF- alpha in PBMCs or of IFN- gamma and IL-10 in adenoidal MNCs, which may be important in modulating pneumococcal carriage in children.

Obsessive-compulsive spectrum disorders and rheumatic fever: a family study

BACKGROUND

Obsessive-compulsive spectrum disorders (OCSDs) are more frequent in patients with active or prior rheumatic fever (RF), suggesting that OCSD and RF may share underlying etiologic mechanisms. Our objective was to estimate the frequency of OCSD in first-degree relatives (FDRs) of RF patients and controls to determine whether there is a familial relationship between OCSD and RF.

METHODS

This is a case-control family study. Of the 98 probands included in this study, 31 had RF without Sydenham's chorea (SC) and had 131 relatives, 28 had RF with SC and had 120 relatives, and 39 were controls without RF. All probands, 87.9% of the RF FDRs and 93.7% of the control FDRs were assessed directly with structured psychiatric interviews and best-estimate diagnoses were assigned. Odds ratios of morbid risks were estimated using logistic regression by the generalized estimating equations (GEE) method and compared between groups.

RESULTS

The rate of OCSDs was significantly higher among FDRs of RF probands than among FDRs of controls (n=37; 14.7% vs. n=10; 7.3%, i=.0279). A diagnosis of OCSDs in an RF proband was associated with a higher rate of OCSDs among FDRs when compared to control FDRs (p-GEE=.02). There was a trend for a higher rate of OCSDs among FDRs of RF probands presenting no OCSD, although the difference was not significant (p-GEE=.09).

CONCLUSION

The results are consistent with the hypothesis that a familial relationship exists between OCSD and RF, since an OCSD in the RF proband was found to increase the risk of OCSDs among FDRs. Additional neuroimmunological and genetic studies involving larger samples are needed to further elucidate this apparent familial relationship between RF and OCSD.

The role of pneumolysin in mediating lung damage in a lethal pneumococcal pneumonia murine model

Background

Intranasal inoculation of Streptococcus pneumoniae D39 serotype 2 causes fatal pneumonia in mice. The cytotoxic and inflammatory properties of pneumolysin (PLY) have been implicated in the pathogenesis of pneumococcal pneumonia.

Methods

To examine the role of PLY in this experimental model we performed ELISA assays for PLY quantification. The distribution patterns of PLY and apoptosis were established by immunohistochemical detection of PLY, caspase-9 activity and TUNEL assay on tissue sections from mice lungs at various times, and the results were quantified with image analysis. Inflammatory and apoptotic cells were also quantified on lung tissue sections from antibody treated mice.

Results

In bronchoalveolar lavages (BAL), total PLY was found at sublytic concentrations which were located in alveolar macrophages and leukocytes. The bronchoalveolar epithelium was PLY-positive, while the vascular endothelium was not PLY reactive. The pattern and extension of cellular apoptosis was similar. Anti-PLY antibody treatment decreased the lung damage and the number of apoptotic and inflammatory cells in lung tissues.

Conclusion

The data strongly suggest that in vivo lung injury could be due to the pro-apoptotic and pro-inflammatory activity of PLY, rather than its cytotoxic activity. PLY at sublytic concentrations induces lethal inflammation in lung tissues and is involved in host cell apoptosis, whose effects are important to pathogen survival.

[Infectious serology: interpretation of the results and traps to avoid]

In Medical Microbiology, in addition to the direct methods of indentification of infectious agentss, the serologic indirect techniques by quantification of antibodies have extremely useful in infectiology, for the diagnosis and the therapeutic or vaccination follow-up as well as for epidemiologic enquiries, serodiagnosis methods have significantly improved. Meanwhile, results may reveal hard to interpret, especially when are tries to specify the time of the beginning of an infection. The results require in the majority of the cases to be compared on two subsequent serum samples, to observe a possible increase in antibodies level. In addition, the infectious serology results may not be considered as the only element of final diagnosis. In all cases, they have to be interpreted and challenged against the clinical context.

Recombinant bactericidal/permeability-increasing protein rBPI21 protects against pneumococcal disease

Bactericidal/permeability-increasing (BPI) protein has been shown to play an important role in innate immunity to gram-negative bacteria, by direct microbicidal as well as endotoxin-neutralizing action. Here we examined potential interactions between a recombinant 21-kDa bioactive fragment of BPI, rBPI21, and the gram-positive pathogen Streptococcus pneumoniae. rBPI21 bound to pneumococci and pneumolysin (Ply) in a direct and specific fashion. We observed an enhanced inflammatory response in mouse macrophages when rBPI21 was combined with killed pneumococci or supernatant from overnight growth of pneumococci. In addition, rBPI21 augmented the proapoptotic activity of Ply+ (but not Ply-) pneumococci in TLR4-defective murine macrophages (known to be defective also in their apoptotic response to pneumolysin) in a tumor necrosis factor alpha-dependent manner. rBPI21 also enhanced the association of pneumococci with murine macrophages. In a model of invasive pneumococcal disease in TLR4-defective mice, the intranasal administration of rBPI21 following intranasal inoculation of Ply+ pneumococci both enhanced upper respiratory tract cell apoptosis and prolonged survival. We have thus discovered a novel interaction between pneumococcus and rBPI21, a potent antimicrobial peptide previously considered to target only gram-negative bacteria.

Increased antistreptococcal antibody titers and anti-basal ganglia antibodies in patients with Tourette syndrome: controlled cross-sectional study

The association between Tourette syndrome, attention-deficit hyperactivity disorder (ADHD), and obsessive-compulsive disorder following streptococcal infections has been documented, but with conflicting reports. We thus felt it was important to investigate this association in a group of Italian patients not previously documented. We took blood on 69 patients with Tourette syndrome and 72 age- and sex-matched tic-free controls. Laboratory staff were blind to the diagnostic status of the subjects. Evidence of recent streptococcal infection was defined using antistreptolysin titers. Anti-basal ganglia antibodies were determined using human basal ganglia sections. Statistical analysis was conducted using analysis of variance and chi-square tests. Raised antistreptolysin titers were found in 41 of 69 (59%) patients with Tourette syndrome and 14 of 72 (19%) controls (P = .000). Positive anti-basal ganglia antibodies were found in 22 of 69 (32%) subjects with Tourette syndrome compared with 7 of 72 (10%) controls, which was also significant (P = .002). Raised antistreptolysin titers were detected in 18 of 22 (82%) patients with Tourette syndrome with positive anti-basal ganglia antibodies and 22 of 47 (47%) patients with negative anti-basal ganglia antibodies (P = .01). These results support the reported association between streptococcal infection and anti-basal ganglia antibodies and some patients with Tourette syndrome.

Regulation of production of mucosal antibody to pneumococcal protein antigens by T-cell-derived gamma interferon and interleukin-10 in children

Nasopharyngeal tonsils (adenoids) are part of human nasopharynx-associated lymphoid tissue, which may play an important role in local defense against pneumococci. Recent studies with animals have suggested that several pneumococcal proteins, including CbpA and pneumolysin (Ply), may be vaccine candidates. Our recent data obtained with children suggest that antibodies to these proteins may protect against carriage. This study was performed to investigate the regulation of the T-cell-dependent antibody responses to CbpA and pneumolysin by cytokines in adenoidal immune cells from children. Adenoidal mononuclear cells (MNC) were cultured with pneumococcal concentrated culture supernatants (CCS) or recombinant proteins. Cytokine expression profiles in adenoidal MNC after antigen stimulation were analyzed by reverse transcription-PCR, protein array analysis, and an immunoassay, along with an antibody production analysis. The roles, interactions, and cellular sources of the main cytokines identified were evaluated further. Pneumococcal CCS induced production of CbpA- and Ply-specific antibodies in association with several chemokines and cytokines, including gamma interferon (IFN-gamma) and interleukin-10 (IL-10) in MNC. The antibody production correlated well with the concentrations of these two cytokines. Addition of recombinant IFN-gamma or IL-10 enhanced antibody production, and monoclonal antibodies to these two cytokines and T-cell depletion significantly reduced antibody production. Intracellular cytokine staining showed that T cells are a major source of IFN-gamma and IL-10. Recombinant Ply and, to a lesser extent, recombinant CbpA induced significant production of IFN-gamma and IL-10 in MNC. T-cell-derived IFN-gamma and IL-10 may be key regulators of production of mucosal antibody to pneumococcal protein antigens in the nasopharynx and may play an important role in local protection against pneumococcal infection in children.

Anti-streptococcal antibodies in the diagnosis of acute and post-streptococcal disease: streptokinase versus streptolysin O and deoxyribonuclease B

AIMS

To establish population normal values and compare the diagnostic value of antibodies against streptokinase (ASK), streptolysin O (ASO) and deoxyribonuclease B (ADNaseB) singularly and in combinations in acute and post-streptococcal disease.

METHODS

A retrospective analysis of serological results was performed to define population norms. Subjects with acute culture-confirmed infection and post-streptococcal disease were assessed using population norms, as were matched controls. The sensitivity and specificity of each antibody assay and of combinations of the different assays were calculated.

RESULTS

Age specific population normal values were derived from 2,321 specimens. None of the three antibodies alone or in combination was a reliable marker of acute streptococcal infection. The sensitivity and specificity of a single antibody titre in post-streptococcal disease ranged from 70.5 to 72.7% and 86.4 to 93.2%, respectively. The combination of ASO and ADNaseB was the most sensitive and specific combination for identifying post-streptococcal disease (sensitivity 95.5%, specificity 88.6%).

CONCLUSIONS

In the diagnosis of acute and post-streptococcal disease, the addition of ASK does not increase the sensitivity or specificity of serological testing. A combination of ASO and ADNaseB is required in post-streptococcal disease to achieve maximum sensitivity and specificity.

DNA vaccines based on genetically detoxified derivatives of pneumolysin fail to protect mice against challenge withStreptococcus pneumoniae

The 7-valent polysaccharide conjugate vaccine currently administered against Streptococcus pneumoniae has been shown to be highly effective in high risk-groups, but its use in developing countries will probably not be possible due to high costs. The use of conserved protein antigens using the genetic vaccination strategy is an interesting alternative for the development of a cost-effective vaccine. We have analyzed the potential of DNA vaccines expressing genetically detoxified derivatives of pneumolysin (pneumolysoids) against pneumococcal infections, and compared this with immunization using recombinant protein. The purified recombinant pneumolysoid with the highest residual cytolytic activity was able to confer partial protection against a lethal intraperitoneal challenge, with the induction of high antibody levels. Immunization with DNA vaccines expressing pneumolysoids, on the other hand, induced a significantly lower antibody response and no protection was observed.

Expression of Recombinant Streptolysin O and Specific Antibody Production

Streptolysin O (SLO), an oxygen-labile cytolysin, is the cholesterol-binding exotoxin of hemolytic streptococci. Besides microbiological and pathological interests, this cytolysin has been used as a tool for permeabilization of biomembranes. SLO serves as a diagnostic reagent for determination of anti-SLO antibody titer in streptococcal infection. Availability of highly purified SLO, however, has been limited by low yield in streptococcal culture and purification process. Present subcloning of mature-type full-length SLO gene into an expression vector having strictly controllable araBAD promoter enabled efficient production of the cytolysin. Further, anti-SLO antibody with high specificity was obtained by immunizing with purified SLO protein.

Construction and immunological characterization of a novel nontoxic protective pneumolysin mutant for use in future pneumococcal vaccines

Pneumolysin, the pore-forming toxin produced by Streptococcus pneumoniae, may have an application as an immunogenic carrier protein in future pneumococcal conjugate vaccines. Most of the 90 S. pneumoniae serotypes identified produce pneumolysin; therefore, this protein may confer non-serotype-specific protection against pneumococcal infections such as pneumonia, meningitis, and otitis media. However, as pneumolysin is highly toxic, a nontoxic form of pneumolysin would be a more desirable starting point in terms of vaccine production. Previous pneumolysin mutants have reduced activity but retain residual toxicity. We have found a single amino acid deletion that blocks pore formation, resulting in a form of pneumolysin that is unable to form large oligomeric ring structures. This mutant is nontoxic at concentrations greater than 1,000 times that of the native toxin. We have demonstrated that this mutant is as immunogenic as native pneumolysin without the associated effects such as production of the inflammatory mediators interleukin-6 and cytokine-induced neutrophil chemoattractant KC, damage to lung integrity, and hypothermia in mice. Vaccination with this mutant protects mice from challenge with S. pneumoniae. Incorporation of this mutant pneumolysin into current pneumococcal vaccines may increase their efficacy.

Identification of invasive serotype 1 pneumococcal isolates that express nonhemolytic pneumolysin

Recently, there has been an increase in invasive pneumococcal disease (IPD) caused by serotype 1 Streptococcus pneumoniae throughout Europe. Serotype 1 IPD is associated with bacteremia and pneumonia in Europe and North America, especially in neonates, and is ranked among the top five most prevalent pneumococcal serotypes in at least 10 countries. The currently licensed pediatric pneumococcal vaccine does not afford protection to this serotype. Upon screening of 252 clinical isolates of S. pneumoniae, we discovered mutations in the pneumolysin gene of two out of the four serotype 1 strains present in the study group. Analysis of an additional 28 serotype 1 isolates from patients with IPD from various Scottish Health Boards, revealed that >50% had mutations in their pneumolysin genes. This resulted in the expression of nonhemolytic forms of pneumolysin. All of the strains producing nonhemolytic pneumolysin were sequence type 306 (ST306), whereas those producing "wild-type" pneumolysin were ST227. The mutations were in a region of pneumolysin involved in pore formation. These mutations can be made in vitro to give the nonhemolytic phenotype. Pneumolysin is generally conserved throughout all serotypes of S. pneumoniae and is essential for full invasive disease; however, it appears that serotype 1 ST306 does not require hemolytically active pneumolysin to cause IPD.