Role of extracellular GAPDH in Streptococcus pyogenes virulence

Pathogens generate molecules, or virulence factors, that enable them to colonize host tissues through several mechanisms, including adhesion to host tissues, or superior invasive capability. Some allow the pathogen to evade the host's immune system. Many of these molecules are proteins that are exported to the cell's surface or secreted. Curiously, GAPDH, which is a glycolytic enzyme, is also a virulence factor that has been shown to contribute to Streptococcus pyogenes pathogenicity by each of these mechanisms.

StreptInCor: a candidate vaccine epitope against S. pyogenes infections induces protection in outbred mice

Infection with Streptococcus pyogenes (S. pyogenes) can result in several diseases, particularly in children. S. pyogenes M protein is the major virulence factor, and certain regions of its N-terminus can trigger autoimmune sequelae such as rheumatic fever in susceptible individuals with untreated group A streptococcal pharyngitis. In a previous study, we utilized a large panel of human peripheral blood cells to define the C-terminal protective epitope StreptInCor (medical identity), which does not induce autoimmune reactions. We recently confirmed the results in HLA-transgenic mice. In the present study, we extended the experimental assays to outbred animals (Swiss mice). Herein, we demonstrate high titers of StreptInCor-specific antibodies, as well as appropriate T-cell immune responses. No cross-reaction to cardiac myosin was detected. Additionally, immunized Swiss mice exhibited 87% survival one month after challenge with S. pyogenes. In conclusion, the data presented herein reinforce previous results in humans and animals and further emphasize that StreptInCor could be an effective and safe vaccine for the prevention of S. pyogenes infections.

Overcoming regulatory T-cell suppression by a lyophilized preparation of Streptococcus pyogenes

Cancer vaccines have yet to yield clinical benefit, despite the measurable induction of humoral and cellular immune responses. As immunosuppression by CD4(+) CD25(+) regulatory T (Treg) cells has been linked to the failure of cancer immunotherapy, blocking suppression is therefore critical for successful clinical strategies. Here, we addressed whether a lyophilized preparation of Streptococcus pyogenes (OK-432), which stimulates Toll-like receptors, could overcome Treg-cell suppression of CD4(+) T-cell responses in vitro and in vivo. OK-432 significantly enhanced in vitro proliferation of CD4(+) effector T cells by blocking Treg-cell suppression and this blocking effect depended on IL-12 derived from antigen-presenting cells. Direct administration of OK-432 into tumor-associated exudate fluids resulted in a reduction of the frequency and suppressive function of CD4(+) CD25(+) Foxp3(+) Treg cells. Furthermore, when OK-432 was used as an adjuvant of vaccination with HER2 and NY-ESO-1 for esophageal cancer patients, NY-ESO-1-specific CD4(+) T-cell precursors were activated, and NY-ESO-1-specific CD4(+) T cells were detected within the effector/memory T-cell population. CD4(+) T-cell clones from these patients had high-affinity TCRs and recognized naturally processed NY-ESO-1 protein presented by dendritic cells. OK-432 therefore inhibits Treg-cell function and contributes to the activation of high-avidity tumor antigen-specific naive T-cell precursors.

Determining antibody-binding site of streptococcal pyrogenic exotoxin B to protect mice from group a streptococcus infection

Streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, is an important virulence factor in group A streptococcal (GAS) infection. SPE B binds and cleaves antibody isotypes and further impairs the immune system by inhibiting complement activation. In this study, we examined the antibody-binding site of SPE B and used it to block SPE B actions during GAS infection. We constructed different segments of the spe B gene and induced them to express different recombinant fragments of SPE B. Using an enzyme-linked immunosorbent assay (ELISA), we found that residues 345–398 of the C-terminal domain of SPE B (rSPE B_345–398), but not the N-terminal domain, was the major binding site for antibody isotypes. Using a competitive ELISA, we also found that rSPE B_345–398 bound to the Fc portion of IgG. The in vitro functional assays indicate that rSPE B_345–398 not only interfered with cleavage of antibody isotypes but also interfered with SPE B-induced inhibition of complement activation. Immunization of BALB/c mice using rSPE B_345–398 was able to induce production of a high titer of anti-rSPE B_345–398 antibodies and efficiently protected mice from GAS-induced death. These findings suggest that SPE B uses its C-terminal domain to bind the Fc portion of IgG and that immunization of mice with this binding domain (rSPE B_345–398) could protect mice from GAS infection.

[Humoral immune response in patients with angina and soft tissue infections of group a streptococci etiology]

Evaluate informativity of simultaneous determination of antibodies (AB) against extracellular (AB against streptolysin-O-ASL-O) and cellular (IgM against A-polysaccharide - A-PSC) antigens in patients with angina and soft tissue infections caused by serogroup A streptococci (SGA) and identify features of humoral immune response to SGA infection according to infectious process localization. MATERIALS AND METHODS. 2 groups of patients with bacteriologically confirmed SGA infection (50 cases of angina - group 1 and 51 case of soft tissue infection - group 2) were examined for the presence of ASL-O by using Architect ci8200 analyzer (Abbott, USA) and IgM against SGA A-PSC by EIA. RESULTS. In group 1, 23 (46%) individuals were recognized as positive by ASL-O level, and in group 2 - 20 (39%; p>0.05); conditionally significant exceeding of normal values (more than 1.5 times) was detected in 25% of patients of each group. Increased level of antibodies against SGA A-PSC was detected in 43 (86%) patients of group 1, and in 30 (59%) of patients of group 2 (p<0.05). In group 1 exceeding of normal values of anti-A-PSC IgM was noted mostly by 1.5 +/- 0.5 times (74%). In group 2 in 43% of patients the level of anti-A-PSC IgM was above normal more than 2 times and in most cases in uncomplicated variants of disease course. In 45% of patients with severe form of soft tissue infection this parameter did not exceed normal values (p<0.05). CONCLUSION. In acute period of disease with simultaneous determination of ASL-O and IgM against A-PSC sensitivity of serologic diagnostics of SGA etiology angina and SGA infection of soft tissues was established to reach 92% and 72%, respectively, and humoral immune response to cellular AG in each form of SGA has its features.

Superantigenic activity of emm3 Streptococcus pyogenes is abrogated by a conserved, naturally occurring smeZ mutation

Streptococcus pyogenes M/emm3 strains have been epidemiologically linked with enhanced infection severity and risk of streptococcal toxic shock syndrome (STSS), a syndrome triggered by superantigenic stimulation of T cells. Comparison of S. pyogenes strains causing STSS demonstrated that emm3 strains were surprisingly less mitogenic than other emm-types (emm1, emm12, emm18, emm28, emm87, emm89) both in vitro and in vivo, indicating poor superantigenic activity. We identified a 13 bp deletion in the superantigen smeZ gene of all emm3 strains tested. The deletion led to a premature stop codon in smeZ, and was not present in other major emm-types tested. Expression of a functional non-M3-smeZ gene successfully enhanced mitogenic activity in emm3 S. pyogenes and also restored mitogenic activity to emm1 and emm89 S. pyogenes strains where the smeZ gene had been disrupted. In contrast, the M3-smeZ gene with the 13 bp deletion could not enhance or restore mitogenicity in any of these S. pyogenes strains, confirming that M3-smeZ is non-functional regardless of strain background. The mutation in M3-smeZ reduced the potential for M3 S. pyogenes to induce cytokines in human tonsil, but not during invasive infection of superantigen-sensitive mice. Notwithstanding epidemiological associations with STSS and disease severity, emm3 strains have inherently poor superantigenicity that is explained by a conserved mutation in smeZ.

Cutting edge issues in rheumatic fever

Although the incidence of acute rheumatic fever and rheumatic heart disease has decreased significantly in regions of the world where antibiotics are easily accessible, there remains a high incidence in developing nations as well as in certain regions where there is a high incidence of genetic susceptibility. These diseases are a function of poverty, low socioeconomic status, and barriers to healthcare access, and it is in the developing world that a comprehensive prevention program is most critically needed. Development of group A streptococcal vaccines has been under investigation since the 1960s and 50 years later, we still have no vaccine. Factors that contribute to this lack of success include a potential risk for developing vaccine-induced rheumatic heart disease, as well as difficulties in covering the many serological subtypes of M protein, a virulence factor found on the surface of the bacterium. Yet, development of a successful vaccine program for prevention of group A streptococcal infection still offers the best chance for eradication of rheumatic fever in the twenty-first century. Other useful approaches include continuation of primary and secondary prevention with antibiotics and implementation of health care policies that provide patients with easy access to antibiotics. Improved living conditions and better hygiene are also critical to the prevention of the spread of group A streptococcus, especially in impoverished regions of the world. The purpose of this article is to discuss current and recent developments in the diagnosis, pathogenesis, and management of rheumatic fever and rheumatic heart disease.

Spectrum and inoculum size effect of a rapid antigen detection test for group A streptococcus in children with pharyngitis

Background

The stability of the accuracy of a diagnostic test is critical to whether clinicians can rely on its result. We aimed to assess whether the performance of a rapid antigen detection test (RADT) for group A streptococcus (GAS) is affected by the clinical spectrum and/or bacterial inoculum size.

Methods

Throat swabs were collected from 785 children with pharyngitis in an office-based, prospective, multicenter study (2009–2010). We analysed the effect of clinical spectrum (i.e., the McIsaac score and its components) and inoculum size (light or heavy GAS growth) on the accuracy (sensitivity, specificity, likelihood ratios and predictive values) of a RADT, with laboratory throat culture as the reference test. We also evaluated the accuracy of a McIsaac-score–based decision rule.

Results

GAS prevalence was 36% (95CI: 33%–40%). The inoculum was heavy for 85% of cases (81%–89%). We found a significant spectrum effect on sensitivity, specificity, likelihood ratios and positive predictive value (p<0.05) but not negative predictive value, which was stable at about 92%. RADT sensitivity was greater for children with heavy than light inoculum (95% vs. 40%, p<0.001). After stratification by inoculum size, the spectrum effect on RADT sensitivity was significant only in patients with light inoculum, on univariate and multivariate analysis. The McIsaac-score–based decision rule had 99% (97%–100%) sensitivity and 52% (48%–57%) specificity.

Conclusions

Variations in RADT sensitivity only occur in patients with light inocula. Because the spectrum effect does not affect the negative predictive value of the test, clinicians who want to rule out GAS can rely on negative RADT results regardless of clinical features if they accept that about 10% of children with negative RADT results will have a positive throat culture. However, such a policy is more acceptable in populations with very low incidence of complications of GAS infection.

DNase Sda1 allows invasive M1T1 Group A Streptococcus to prevent TLR9-dependent recognition

Group A Streptococcus (GAS) has developed a broad arsenal of virulence factors that serve to circumvent host defense mechanisms. The virulence factor DNase Sda1 of the hyperinvasive M1T1 GAS clone degrades DNA-based neutrophil extracellular traps allowing GAS to escape extracellular killing. TLR9 is activated by unmethylated CpG-rich bacterial DNA and enhances innate immune resistance. We hypothesized that Sda1 degradation of bacterial DNA could alter TLR9-mediated recognition of GAS by host innate immune cells. We tested this hypothesis using a dual approach: loss and gain of function of DNase in isogenic GAS strains and presence and absence of TLR9 in the host. Either DNA degradation by Sda1 or host deficiency of TLR9 prevented GAS induced IFN-α and TNF-α secretion from murine macrophages and contributed to bacterial survival. Similarly, in a murine necrotizing fasciitis model, IFN-α and TNF-α levels were significantly decreased in wild type mice infected with GAS expressing Sda1, whereas no such Sda1-dependent effect was seen in a TLR9-deficient background. Thus GAS Sda1 suppressed both the TLR9-mediated innate immune response and macrophage bactericidal activity. Our results demonstrate a novel mechanism of bacterial innate immune evasion based on autodegradation of CpG-rich DNA by a bacterial DNase.

Multi high-throughput approach for highly selective identification of vaccine candidates: the Group A Streptococcus case

We propose an experimental strategy for highly accurate selection of candidates for bacterial vaccines without using in vitro and/or in vivo protection assays. Starting from the observation that efficacious vaccines are constituted by conserved, surface-associated and/or secreted components, the strategy contemplates the parallel application of three high throughput technologies, i.e. mass spectrometry-based proteomics, protein array, and flow-cytometry analysis, to identify this category of proteins, and is based on the assumption that the antigens identified by all three technologies are the protective ones. When we tested this strategy for Group A Streptococcus, we selected a total of 40 proteins, of which only six identified by all three approaches. When the 40 proteins were tested in a mouse model, only six were found to be protective and five of these belonged to the group of antigens in common to the three technologies. Finally, a combination of three protective antigens conferred broad protection against a panel of four different Group A Streptococcus strains. This approach may find general application as an accelerated and highly accurate path to bacterial vaccine discovery.

Immunological evaluation of lipopeptide group A streptococcus (GAS) vaccine: structure-activity relationship

Streptococcus pyogenes (group A streptococcus, GAS) is a Gram-positive bacterial pathogen responsible for a wide variety of diseases. To date, GAS vaccine development has focused primarily on the M-protein. The M-protein is highly variable at the amino (N)-terminus (determining serotype) but is conserved at the carboxyl (C)-terminus. Previously a 29 amino acid peptide (named J14) from the conserved region of the M-protein was identified as a potential vaccine candidate. J14 was capable of eliciting protective antibodies that recognized many GAS serotypes when co-administered with immuno-stimulants. This minimal epitope however showed no immunogenicity when administered alone. In an attempt overcome this immunological non-responsiveness, we developed a self-adjuvanting vaccine candidate composed of three components: the B-cell epitope (J14), a universal helper T-cell epitope (P25) and a lipid moiety consisting of lipoamino acids (Laas) which target Toll-like receptor 2 (TLR2). Immunological evaluation in B10.BR (H-2k) mice demonstrated that the epitope attachment to the point of lipid moiety, and the length of the Laa alkyl chain have a profound effect on vaccine immunogenicity after intranasal administration. It was demonstrated that a vaccine featuring C-terminal lipid moiety containing alkyl chains of 16 carbons, with P25 located at the N-terminus, and J14 attached to the side chain of a central lysine residue was capable of inducing optimal antibody response. These findings have considerable relevance to the development of a broad spectrum J14-based GAS vaccine and in particular provided a rational basis for peptide vaccine design based on this self-adjuvanting lipopeptide technology.

Group a streptococcal vaccine candidates: potential for the development of a human vaccine

Currently there is no commercial Group A Streptococcus (GAS; S. pyogenes) vaccine available. The development of safe GAS vaccines is challenging, researchers are confronted with obstacles such as the occurrence of many unique serotypes (there are greater than 150 M types), antigenic variation within the same serotype, large variations in the geographical distribution of serotypes, and the production of antibodies cross-reactive with human tissue which can lead to host auto-immune disease. Cell wall anchored, cell membrane associated, secreted and anchorless proteins have all been targeted as GAS vaccine candidates. As GAS is an exclusively human pathogen, the quest for an efficacious vaccine is further complicated by the lack of an animal model which mimics human disease and can be consistently and reproducibly colonized by multiple GAS strains.

Robust antigen specific th17 T cell response to group A Streptococcus is dependent on IL-6 and intranasal route of infection

Group A streptococcus (GAS, Streptococcus pyogenes) is the cause of a variety of clinical conditions, ranging from pharyngitis to autoimmune disease. Peptide-major histocompatibility complex class II (pMHCII) tetramers have recently emerged as a highly sensitive means to quantify pMHCII-specific CD4⁺ helper T cells and evaluate their contribution to both protective immunity and autoimmune complications induced by specific bacterial pathogens. In lieu of identifying an immunodominant peptide expressed by GAS, a surrogate peptide (2W) was fused to the highly expressed M1 protein on the surface of GAS to allow in-depth analysis of the CD4⁺ helper T cell response in C57BL/6 mice that express the I-A^b MHCII molecule. Following intranasal inoculation with GAS-2W, antigen-experienced 2W:I-A^b-specific CD4⁺ T cells were identified in the nasal-associated lymphoid tissue (NALT) that produced IL-17A or IL-17A and IFN-γ if infection was recurrent. The dominant Th17 response was also dependent on the intranasal route of inoculation; intravenous or subcutaneous inoculations produced primarily IFN-γ⁺ 2W:I-A^b+ CD4⁺ T cells. The acquisition of IL-17A production by 2W:I-A^b-specific T cells and the capacity of mice to survive infection depended on the innate cytokine IL-6. IL-6-deficient mice that survived infection became long-term carriers despite the presence of abundant IFN-γ-producing 2W:I-A^b-specific CD4⁺ T cells. Our results suggest that an imbalance between IL-17- and IFN-γ-producing CD4⁺ T cells could contribute to GAS carriage in humans.

Group A streptococcus (GAS) causes many different conditions, ranging from strep throat, flesh eating disease to post infectious complications involving the heart. Here, we used a novel technique to study the CD4⁺ T cell immune response against GAS infection in a mouse model. We first generated a recombinant GAS strain that expresses a specific epitope (2W) - M protein fusion and used this to intranasally inoculate mice. Peptide specific CD4⁺ T cells were concentrated and analyzed using 2W-MHC-II tetramers. This technology allowed us to probe the antigen specific CD4⁺ T cell response to new depths and certainty. Infection induced a robust 2W-specific Th17 cell response, which was dependent on the route of infection, IL-6, and was independent of superantigens. IL-6^-/- mice were exquisitely susceptible to intranasal infection. However, those that survived became immune carriers, unable to clear streptococci from NALT. Further, multiple infections generated an IL-17⁺ IFN-γ⁺ double positive population of CD4⁺ T cells that are known to be associated with autoimmune disease in humans and directly responsible for autoimmune pathology in rodent models. Our results provide a new direction for understanding two important consequences of streptococcal pharyngitis, the very common immune carrier state, and the rarer state involving autoimmune complications.

HLA class II transgenic mice develop a safe and long lasting immune response against StreptInCor, an anti-group A streptococcus vaccine candidate

Streptococcus pyogenes infections remain a health problem in several countries because of post-streptococcal sequelae, such as rheumatic fever and rheumatic heart disease. We developed a vaccine epitope (StreptInCor) composed of 55 amino acid residues of the C-terminal portion of the M protein that encompasses both T and B cell protective epitopes. Recently, by using human blood samples, we showed that the StreptInCor epitope is able to bind to different HLA class II molecules and that it could be considered a universal vaccine epitope. In the present work, we evaluated the immune response of HLA class II transgenic mice against aluminum hydroxide-absorbed StreptInCor. After a period of one year, several organs were analyzed histologically to verify the safety of the candidate vaccine epitope. Our results showed that StreptInCor is able to induce robust and safe and long lasting immune response without deleterious reactions in several organs. In conclusion, the results presented here indicate that StreptInCor could be considered a safe vaccine against severe streptococcus-induced diseases.

Immunologic impact of tonsillopharyngitis associated with group A streptococci

While very common clinically, group A streptococcal infections of the upper respiratory tract remain incompletely understood. Vital to clarifying these incompletely answered questions is the understanding of the immune responses associated with infection and the enigmatic 'carrier state'. An important aspect of this is understanding the differences between an immune response and a protective immune response. Several of these concerns are discussed.

[Serotypes and antimicrobial susceptibilities of invasive group A streptococci identified in eastern Black Sea region of Turkey]

Frequency of invasive group A streptococcus (GAS) infections is increasing worldwide in recent 20 years. Serotypes responsible for these clinical manifestations and their antibiotic susceptibilities should be known in order to establish preventive measures and initiate appropriate treatment. This study was aimed to determine the serotypes, antibiotic susceptibilities and inducible clindamycin resistance among invasive GAS isolated between 2006-2009 period. A total of 22 GAS strains isolated from clinical samples [sterile body fluids (peritoneal, pleural, pericardial, joint and cerebrospinal fluids), blood, tissue biopsy] of the patients (14 male, 8 female; age range: 3-82 years, median age: 59) who admitted to Karadeniz Technical University Faculty of Medicine, Farabi Hospital located in Trabzon province (Eastern Black Sea Region of Turkey), between March 2006 and March 2009 were included in the study. GAS serotypes were determined by the investigation of serum opacity factors (SOF), T proteins and M proteins. SOF production was investigated by microplate method using human serum and SOF types were determined by SOF-inhibition test using specific antisera. T protein types were detected by agglutination method using polyvalent anti-T sera, and M serotypes were detected by capillary precipitation method using M antisera. Antimicrobial susceptibility tests were performed by disk-diffusion method according to CLSI recommendations. SOF were positive in 9 (41%) samples. Use of T antiserum yielded T (n= 8) and U (n= 7) types and M antiserum M1 (n= 4) and M2 (n= 3) types. The overall antibiotic susceptibility rate of the isolates was 68% (15/22) and overall resistance rate was 32% (7/22). All of the GAS strains were found susceptible to benzylpenicillin, ceftriaxone, vancomycin, levofloxacine and linezolid, however 9 (41%) were intermediate susceptible to tetracycline and 1 (4.5%) was intermediate susceptible to erythromycin. Four (18%) strains were found resistant to tetracycline, while three strains (13.5%) were found resistant to chloramphenicol. Inducible clindamycin resistance was found positive only in one strain. The serotypes determined in this study indicated that 33% of our invasive serotypes were covered by the hexavalent vaccine and 62% by the 26-valent vaccine. Multi-center surveillance studies are required to determine the serotype distribution of invasive GAS in Turkey and to provide valuable information for the development of appropriate vaccines in our country.

Mapping the protein-protein interface between a toxin and its cognate antitoxin from the bacterial pathogen Streptococcus pyogenes

Protein--protein interactions are ubiquitous and essential for most biological processes. Although new proteomic technologies have generated large catalogs of interacting proteins, considerably less is known about these interactions at the molecular level, information that would aid in predicting protein interactions, designing therapeutics to alter these interactions, and understanding the effects of disease-producing mutations. Here we describe mapping the interacting surfaces of the bacterial toxin SPN (Streptococcus pyogenes NAD(+) hydrolase) in complex with its antitoxin IFS (immunity factor for SPN) by using hydrogen-deuterium amide exchange and electrospray ionization mass spectrometry. This approach affords data in a relatively short time for small amounts of protein, typically 5-7 pmol per analysis. The results show a good correspondence with a recently determined crystal structure of the IFS--SPN complex but additionally provide strong evidence for a folding transition of the IFS protein that accompanies its binding to SPN. The outcome shows that mass-based chemical footprinting of protein interaction surfaces can provide information about protein dynamics that is not easily obtained by other methods and can potentially be applied to large, multiprotein complexes that are out of range for most solution-based methods of biophysical analysis.

Inactivated and live, attenuated influenza vaccines protect mice against influenza: Streptococcus pyogenes super-infections

Mortality associated with influenza virus super-infections is frequently due to secondary bacterial complications. To date, super-infections with Streptococcus pyogenes have been studied less extensively than those associated with Streptococcus pneumoniae. This is significant because a vaccine for S. pyogenes is not clinically available, leaving vaccination against influenza virus as our only means for preventing these super-infections. In this study, we directly compared immunity induced by two types of influenza vaccine, either inactivated influenza virus (IIV) or live, attenuated influenza virus (LAIV), for the ability to prevent super-infections. Our data demonstrate that both IIV and LAIV vaccines induce similar levels of serum antibodies, and that LAIV alone induces IgA expression at mucosal surfaces. Upon super-infection, both vaccines have the ability to limit the induction of pro-inflammatory cytokines within the lung, including IFN-γ which has been shown to contribute to mortality in previous models of super-infection. Limiting expression of these pro-inflammatory cytokines within the lungs subsequently limits recruitment of macrophages and neutrophils to pulmonary surfaces, and ultimately protects both IIV- and LAIV-vaccinated mice from mortality. Despite their overall survival, both IIV- and LAIV-vaccinated mice demonstrated levels of bacteria within the lung tissue that are similar to those seen in unvaccinated mice. Thus, influenza virus:bacteria super-infections can be limited by vaccine-induced immunity against influenza virus, but the ability to prevent morbidity is not complete.

A novel monoclonal antibody against FbaA can inhibit the binding of the complement regulatory protein factor H to group A streptococcus

Some microbial pathogens utilize human complement regulatory proteins, such as factor H (FH) and factor H-like protein 1 (FHL-1), for immune evasion. FbaA is an FHL-1 and FH binding protein expressed on the surface of group A streptococcus (GAS), a common agent of pharyngeal, skin, and soft tissue infections. In this study, we prepared monoclonal antibodies (MAbs) against FbaA, assayed them for specificity, and located their binding domains in FbaA. We found an MAb called FbaA MAb2, which demonstrated the highest affinity to GAS among all of the MAbs. Based on the binding with component peptides, the detected epitope, which was specific for FbaA MAb2, was the amino acid residues 95 to 118 of FbaA; on the other hand, it did not bind with the truncated protein of the internally deleted residues of the segment from 95 to 118 of FbaA. Furthermore, the predominant amino acids specific for FbaA MAb2 screened by phage display epitope library were I, T, P, D, and L, corresponding to the amino acid residues 101, 103, 105, 106, and 110 of FbaA, respectively. The binding location of FbaA with FH and FHL-1 was a 16-amino-acid region corresponding to amino acid residues 97 to 112 of FbaA, which overlapped the FbaA MAb2 binding domain, as confirmed by competitive inhibition enzyme-linked immunosorbent assay and immunofluorescence microscopy. Based on the results of the invasion assay, FbaA MAb2 can inhibit the binding of FH to GAS.

CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III

CRISPR/Cas systems constitute a widespread class of immunity systems that protect bacteria and archaea against phages and plasmids, and commonly use repeat/spacer-derived short crRNAs to silence foreign nucleic acids in a sequence-specific manner. Although the maturation of crRNAs represents a key event in CRISPR activation, the responsible endoribonucleases (CasE, Cas6, Csy4) are missing in many CRISPR/Cas subtypes. Here, differential RNA sequencing of the human pathogen Streptococcus pyogenes uncovered tracrRNA, a trans-encoded small RNA with 24-nucleotide complementarity to the repeat regions of crRNA precursor transcripts. We show that tracrRNA directs the maturation of crRNAs by the activities of the widely conserved endogenous RNase III and the CRISPR-associated Csn1 protein; all these components are essential to protect S. pyogenes against prophage-derived DNA. Our study reveals a novel pathway of small guide RNA maturation and the first example of a host factor (RNase III) required for bacterial RNA-mediated immunity against invaders.

Anti-group A streptococcal vaccine epitope: structure, stability, and its ability to interact with HLA class II molecules

Streptococcus pyogenes infections remain a health problem in several countries due to poststreptococcal sequelae. We developed a vaccine epitope (StreptInCor) composed of 55 amino acids residues of the C-terminal portion of the M protein that encompasses both T and B cell protective epitopes. The nuclear magnetic resonance (NMR) structure of the StreptInCor peptide showed that the structure was composed of two microdomains linked by an 18-residue α-helix. A chemical stability study of the StreptInCor folding/unfolding process using far-UV circular dichroism showed that the structure was chemically stable with respect to pH and the concentration of urea. The T cell epitope is located in the first microdomain and encompasses 11 out of the 18 α-helix residues, whereas the B cell epitope is in the second microdomain and showed no α-helical structure. The prediction of StreptInCor epitope binding to different HLA class II molecules was evaluated based on an analysis of the 55 residues and the theoretical possibilities for the processed peptides to fit into the P1, P4, P6, and P9 pockets in the groove of several HLA class II molecules. We observed 7 potential sites along the amino acid sequence of StreptInCor that were capable of recognizing HLA class II molecules (DRB1*, DRB3*, DRB4*, and DRB5*). StreptInCor-overlapping peptides induced cellular and humoral immune responses of individuals bearing different HLA class II molecules and could be considered as a universal vaccine epitope.

Antibacterial activity of the contact and complement systems is blocked by SIC, a protein secreted by Streptococcus pyogenes

Recent studies have shown that activation of complement and contact systems results in the generation of antibacterial peptides. Streptococcus pyogenes, a major bacterial pathogen in humans, exists in >100 different serotypes due to sequence variation in the surface-associated M protein. Cases of invasive and life-threatening S. pyogenes infections are commonly associated with isolates of the M1 serotype, and in contrast to the large majority of M serotypes, M1 isolates all secrete the SIC protein. Here, we show that SIC interferes with the activation of the contact system and blocks the activity of antibacterial peptides generated through complement and contact activation. This effect promotes the growth of S. pyogenes in human plasma, and in a mouse model of S. pyogenes sepsis, SIC enhances bacterial dissemination, results which help explain the high frequency of severe S. pyogenes infections caused by isolates of the M1 serotype.

[Immunization of mice by group A streptococci and its effect on bone marrow stromal cells and level of serum cytokines]

AIM

To assess effect of continued immunization of mice from CBA line with inactivated group A streptococcal vaccine on levels of serum cytokines and number of stromal bone marrow progenitor cells in immunized mice and in heterotopic transplants after different variants of transplantation.

MATERIALS AND METHODS

CBA mice were immunized during 3 weeks with heat-killed vaccine prepared from group A streptococci type 5. Levels of pro- and antiinflammatory cytokines were measured with BioPlex device. Number of stromal progenitor cells was determined on quantity of colonies formed by cells explanted to monolayer cultures.

RESULTS

Significant 2.3-fold increase of number of stromal progenitor cells in femoral bone marrow of immune mice was demonstrated. Experiments with heterotopic transplants showed that bone marrow in transplants of mice immunized with streptococci--variant Normal-->Immune (N-->1)-- is defective both on efficacy of cloning and number of stromal progenitor cells. Even short-term presence of stromal tissue in immune organism (variant I -->N) significantly changed these parameters, especially at late time after transplantation. In serum of immune mice changes of cytokines levels, especially TNFalpha, were observed. The level of the latter was decreased (mean--2.5-fold) in all immune serum samples compared to normal serum.

CONCLUSION

Immunization of mice with group A streptococci leads to changes in stromal tissue and, possibly, to damage of microenvironment functions including hemo- and lymphopoiesis.

[Multifocal inflammatory syndrome after invasive infection due to an M1 strain of Streptococcus pyogenes]

We report on a case of Streptococcus pyogenes invasive disease with toxic shock syndrome due to an M1 strain producing SpeA and SmeZ superantigenic toxins. Post-streptococcal sequelae included several episodes of reactive arthritis and orchitis whose outcome was favorable with corticosteroid therapy. Invasive streptococcal infections are increasingly reported and may associate septic, toxinic, and immunological diseases. High-grade systemic inflammation may induce nonsuppurative complications and autoimmune diseases by molecular mimicry. Among them, reactive arthritis has been recognized as a separate entity from acute rheumatic fever and post-streptococcal orchitis has not been described before. Treatment should be quickly started and should be effective on the etiologic agent but also on its toxins due to the severity of the invasive infections associated with the spread of highly virulent bacterial clones and the potential development of multifocal nonsuppurative sequelae.