Global antibody response to Staphylococcus aureus live-cell vaccination

Immunoinformatic prediction to identify Staphylococcus aureus peptides that bind to CD8+ T-cells as potential vaccine candidates

Background and Aim

Staphylococcus aureus, with its diverse virulence factors and immune response evasion mechanisms, presents a formidable challenge as an opportunistic pathogen. Developing an effective vaccine against S. aureus has proven elusive despite extensive efforts. Autologous Staphylococcus lysate (ASL) treatment has proven effective in triggering an immune response against bovine mastitis. Peptides that stimulate the immune response can be the subject of further research. The study aimed to use immunoinformatics tools to identify epitopes on S. aureus surface and secretory proteins that can bind to major histocompatibility complex class I (MHC I) and CD8+ T-cells. This method aids in discovering prospective vaccine candidates and elucidating the rationale behind ASL therapy's efficacy.

Materials and Methods

Proteins were identified using both literature search and the National Center for Biotechnology Information search engine Entrez. Self and non-self peptides, allergenicity predictions, epitope locations, and physicochemical characteristics were determined using sequence alignment, AllerTOP, SVMTriP, and Protein-Sol tools. Hex was employed for simulating the docking interactions between S. aureus proteins and the MHC I + CD8+ T-cells complex. The binding sites of S. aureus proteins were assessed using Computer Atlas of Surface Topography of Proteins (CASTp) while docked with MHC I and CD8+ T-cells.

Results

Nine potential S. aureus peptides and their corresponding epitopes were identified in this study, stimulating cytotoxic T-cell mediated immunity. The peptides were analyzed for similarity with self-antigens and allergenicity. 1d20, 2noj, 1n67, 1nu7, 1amx, and 2b71, non-self and stable, are potential elicitors of the cytotoxic T-cell response. The energy values from docking simulations of peptide-MHC I complexes with the CD8+ and T-cell receptor (TCR) indicate the stability and strength of the formed complexes. These peptides - 2noj, 1d20, 1n67, 2b71, 1nu7, 1yn3, 1amx, 2gi9, and 1edk - demonstrated robust MHC I binding, as evidenced by their low binding energies. Peptide 2gi9 exhibited the lowest energy value, followed by 2noj, 1nu7, 1n67, and 1d20, when docked with MHC I and CD8 + TCR, suggesting a highly stable complex. CASTp analysis indicated substantial binding pockets in the docked complexes, with peptide 1d20 showing the highest values for area and volume, suggesting its potential as an effective elicitor of immunological responses. These peptides - 2noj, 2gi9, 1d20, and 1n67 - stand out for vaccine development and T-cell activation against S. aureus.

Conclusion

This study sheds light on the design and development of S. aureus vaccines, highlighting the significance of employing computational methods in conjunction with experimental verification. The significance of T-cell responses in combating S. aureus infections is emphasized by this study. More experiments are needed to confirm the effectiveness of these vaccine candidates and discover their possible medical uses.

Microchimeric cells promote production of rheumatoid arthritis-specific autoantibodies

BACKGROUND

Women are more likely to develop autoimmune diseases than men. Contribution from microchimerism (Mc) has been proposed, as women naturally acquire Mc from more sources than men because of pregnancy. Women with Rheumatoid Arthritis (RA) who lack RA-associated HLA alleles have been found to harbor Mc with RA-associated HLA alleles in higher amounts than healthy women in prior work. However, an immunological impact of Mc remains to be elucidated.

OBJECTIVES

To test the hypothesis that Mc with RA-risk associated HLA alleles can result in the production of RA-associated autoantibodies, when host genetic risk is absent.

METHODS

DBA/2 mice are unable to produce RA-specific anti-citrullinated autoantibodies (ACPAs) after immunization with the enzyme peptidyl arginine deiminase (PAD) in a previously developed model. DBA/2 females were mated with C57BL/6 males humanized to express HLA-DR4, which is associated with RA-risk and production of ACPAs, to evaluate DR4+ fetal Mc contribution. Next, DBA/2 females born of heterozygous DR4+/- mothers were evaluated for DR4+ Mc of maternal or littermate origin. Finally, DBA/2 females from DR4+/- mothers were crossed with DR4+ males, to evaluate the contribution of any Mc source to ACPA production.

RESULTS

After PAD immunization, between 20 % and 43 % of DBA/2 females (otherwise unable to produce ACPAs) had detectable ACPAs (CCP2 kit) after exposure to sources of Mc with RA-associated HLA alleles, compared to 0 % of unmated/unexposed DBA/2 females. Further the microchimeric origin of the autoantibodies was confirmed by detecting a C57BL/6-specific immunoglobulin isotype in the DBA/2 response.

CONCLUSION

Our study demonstrates that Mc cells can produce "autoantibodies" and points to a role of Mc in the biology of autoimmune diseases, including RA.

The Role of the Oral Immune System in Oropharyngeal Candidiasis-Facilitated Invasion and Dissemination of Staphylococcus aureus

Candida albicans and Staphylococcus aureus account for most invasive fungal and bacterial bloodstream infections (BSIs), respectively. However, the initial point of invasion responsible for S. aureus BSIs is often unclear. Recently, C. albicans has been proposed to mediate S. aureus invasion of immunocompromised hosts during co-colonization of oral mucosal surfaces. The status of the oral immune system crucially contributes to this process in two distinct ways: firstly, by allowing invasive C. albicans growth during dysfunction of extra-epithelial immunity, and secondly following invasion by some remaining function of intra-epithelial immunity. Immunocompromised individuals at risk of developing invasive oral C. albicans infections could, therefore, also be at risk of contracting concordant S. aureus BSIs. Considering the crucial contribution of both oral immune function and dysfunction, the aim of this review is to provide an overview of relevant aspects of intra and extra-epithelial oral immunity and discuss predominant immune deficiencies expected to facilitate C. albicans induced S. aureus BSIs.

Long-Term Sinonasal Carriage of Staphylococcus aureus and Anti-Staphylococcal Humoral Immune Response in Patients with Chronic Rhinosinusitis

We investigated Staphylococcus aureus diversity, genetic factors, and humoral immune responses against antigens via genome analysis of S. aureus isolates from chronic rhinosinusitis (CRS) patients in a long-term follow-up. Of the 42 patients who provided S. aureus isolates and serum for a previous study, 34 could be included for follow-up after a decade. Clinical examinations were performed and bacterial samples were collected from the maxillary sinus and nares. S. aureus isolates were characterized by whole-genome sequencing, and specific anti-staphylococcal IgG in serum was determined using protein arrays. S. aureus was detected in the nares and/or maxillary sinus at both initial inclusion and follow-up in 15 of the 34 respondents (44%). Three of these (20%) had S. aureus isolates from the same genetic lineage as at inclusion. A low number of single-nucleotide polymorphisms (SNPs) were identified when comparing isolates from nares and maxillary sinus collected at the same time point. The overall change of antibody responses to staphylococcal antigens over time showed great variability, and no correlation was found between the presence of genes encoding antigens and the corresponding anti-staphylococcal IgG in serum; thus our findings did not support a role, in CRS, of the specific S. aureus antigens investigated.

Antibody levels to Malassezia pachydermatis and Staphylococcus pseudintermedius in atopic dogs and their relationship with lesion scores

BACKGROUND

Elevated immunoglobulin E (IgE) levels to Malassezia or Staphylococcus species in human atopic dermatitis are related to the skin severity index; a similar association has not been reported in atopic dogs.

OBJECTIVES

To investigate serum levels of allergen-specific IgE, total specific IgG and IgG subclasses (IgG1 and IgG2) for M. pachydermatis and S. pseudintermedius, and to correlate them with the severity of dermatitis in dogs.

ANIMALS

Serum samples were collected from dogs categorized by age and disease status. Groups 1 and 2: <3-year-old healthy (n = 9) and atopic dogs (n = 9), respectively; and groups 3 and 4: ≥3-year-old healthy (n = 11) and atopic dogs (n = 14), respectively.

METHODS AND MATERIALS

Antibody levels were measured by ELISA. The Canine Atopic Dermatitis Lesion Index (CADLI) was analyzed in relation to antibody levels.

RESULTS

Specific IgE and total IgG against M. pachydermatis and S. pseudintermedius were significantly increased in atopic dogs of all ages. Although differences between atopic and healthy dogs, with regard to specific IgG1 and IgG2 levels to each microbe, varied in significance within age groups. No significant relationships were found between the CADLI and any specific immunoglobulin levels for both microbe types.

CONCLUSIONS AND CLINICAL IMPORTANCE

In dog skin, microbes may act as allergens triggering inflammatory responses via IgE- and IgG-dependent pathway(s). The affinity of the IgG subclass produced may vary according to antigen type. Specific IgE levels may be related to clinical disease in dogs and not to skin lesion severity.

Genotyping of methicillin-resistant Staphylococcus aureus from sepsis patients in Pakistan and detection of antibodies against staphylococcal virulence factors

In order to obtain more information on the MRSA population structure in the border region of Afghanistan and Pakistan, we collected and genotyped MRSA causing bloodstream infections from a tertiary care hospital in Peshawar, Pakistan, that serves the local population as well as Afghan immigrants and refugees. Thirty-one MRSA isolates from 30 patients were included and characterized by microarray hybridisation. For 25 patients, serum samples were tested using protein microarrays in order to detect antibodies against staphylococcal virulence factors. The most conspicuous result was the high rate of PVL-positive MRSA. Twenty-two isolates (71%) harboured lukF/S-PV genes. The most common lineage was CC772-MRSA-V/VT (PVL+) to which eleven isolates were assigned. The second most common strain was, surprisingly, CC8-MRSA-[IV+ACME] (PVL+), "USA300" (9 isolates). Two isolates were tst1 positive CC22-MRSA-IV, matching the Middle Eastern "Gaza Epidemic Strain". Another two were PVL-positive CC30-MRSA-IV. The remaining isolates belonged to, possibly locally emerging, CC1, CC5, and CC8 strains with SCC mec IV elements. Twenty-three patient sera were positive for anti-PVL-IgG antibodies. Several questions arise from the present study. It can be assumed that MRSA and high rates of PVL-positive S. aureus/MRSA are a public health issue in the Afghanistan/Pakistan border region. A possible emergence of the "USA300" clone as well as of the CC772 lineage warrants further investigation.

Development of a miniaturized protein microarray as a new serological IgG screening test for zoonotic agents and production diseases in pigs

In order to monitor the occurrence of zoonotic agents in pig herds as well as to improve herd health management, the development of new cost-effective diagnostic methods for pigs is necessary. In this study, a protein microarray-based assay for the simultaneous detection of immunoglobulin G (IgG) antibodies against different zoonotic agents and pathogens causing production diseases in pigs was developed. Therefore, antigens of ten different important swine pathogens (Toxoplasma gondii, Yersinia enterocolitica, Salmonella spp., Trichinella spp., Mycobacterium avium, Hepatitis E virus, Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, the porcine reproductive and respiratory syndrome virus, Influenza A virus) were spotted and covalently immobilized as 'antigen-spots' on microarray chips in order to test pig serum for the occurrence of antibodies. Pig serum was sampled at three German abattoirs and ELISA tests for the different pathogens were conducted with the purpose of creating a panel of reference samples for microarray analysis. To evaluate the accuracy of the antigens on the microarray, receiver operating characteristic (ROC) curve analysis using the ELISA test results as reference was performed for the different antigens. High area under curve values were achieved for the antigens of two zoonotic agents: Toxoplasma gondii (0.91), Yersinia enterocolitica (0.97) and for three production diseases: Actinobacillus pleuropneumoniae (0.77), Mycoplasma hyopneumoniae (0.94) and the porcine reproductive and respiratory syndrome virus (0.87). With the help of the newly developed microarray assay, collecting data on the occurrence of antibodies against zoonotic agents and production diseases in pig herds could be minimized to one measurement, resulting in an efficient screening test.

Label-free detection of Staphylococcus aureus bacteria using long-period fiber gratings with functional polyelectrolyte coatings

Highly sensitive long-period fiber gratings (LPFG) was developed for label-free and rapid detection of Staphylococcus aureus (S. aureus). Specifically, the LPFG was functionalized with antibody and nanopitted polyelectrolyte coatings to facilitate bacterial adhesion and thus enhance the sensitivity of bacteria detection. The kinetics of S. aureus adhesion on functional coatings were tracked by surface morphology evolution and time-resolved resonance wavelength shift of the coated LPFG at a flow rate of 30 μl/ml and 37 °C in the concentration range of 10⁴-10⁸ colony forming unit (CFU)/ml. S. aureus detection at concentrations as low as 224 CFU/ml can be achieved within a short time span of 30 min. The LPFG-based biosensor can be readily adapted to a variety of biophotonic platforms, for applications such as food safety inspection, environmental monitoring, clinical diagnostics, and medical applications.

Individual variation is the key to the development of a vaccine against Staphylococcus aureus: a comparative study between mice lineages

Bacterial infections occur worldwide and are a major public health problem. Among pathogens, Staphylococcus aureus is the main causative agent of bacterial diseases in the world. This study aimed to evaluate which components of the immune system could act protectively against a S. aureus infection in intradermally immunized mice. C57BL/6 and A/j mice were immunized intradermally with S. aureus inactivated by heat and then challenged with viable strains in an air pouch model. At 6, 12, and 24 h after the challenge, euthanasia was performed, and the cellular profile of the inflammatory infiltrate, cytokines, and the bacterial load were evaluated in the air pouch lavages. Immunized mice demonstrated that the intradermal immunization with S. aureus promoted protection in C57BL/6 mice by reducing the bacterial, which was correlated with increased serum concentration of IgG antibodies (IgG1 and IgG2a) against S. aureus. The increase in IgG2a antibody levels was correlated with a decrease of bacterial load in intradermally immunized C57BL/6 mice, along with production of IL-17A at the inflammation site, as well as IgG1consumption. Similar results were not found in the A/j lineage. In conclusion, a vaccine against S. aureus should focus more on the individual characteristics of the host because it is a determinant factor for the success of the immunization.

A novel synthetic peptide microarray assay detects Chlamydia species-specific antibodies in animal and human sera

Serological analysis of Chlamydia (C.) spp. infections is still mainly based on micro-immunofluorescence and ELISA. To overcome the limitations of conventional serology, we have designed a novel microarray carrying 52 synthetic peptides representing B-cell epitopes from immunodominant proteins of all 11 chlamydial species. The new assay has been validated using monospecific mouse hyperimmune sera. Subsequently, serum samples from cattle, sheep and humans with a known history of chlamydial infection were examined. For instance, the specific humoral response of sheep to treatment with a C. abortus vaccine has been visualized against a background of C. pecorum carriership. In samples from humans, dual infection with C. trachomatis and C. pneumoniae could be demonstrated. The experiments revealed that the peptide microarray assay was capable of simultaneously identifying specific antibodies to each Chlamydia spp. The actual assay represents an open platform test that can be complemented through future advances in Chlamydia proteome research. The concept of the highly parallel multi-antigen microarray proven in this study has the potential to enhance our understanding of antibody responses by defining not only a single quantitative response, but also the pattern of this response. The added value of using peptide antigens will consist in unprecedented serodiagnostic specificity.

Human Memory B Cells Targeting Staphylococcus aureus Exotoxins Are Prevalent with Skin and Soft Tissue Infection

Staphylococcus aureus is a Gram-positive opportunistic pathogen that causes superficial and invasive infections in the hospital and community. High mortality from infection emphasizes the need for improved methods for prevention and treatment. Although S. aureus possesses an arsenal of virulence factors that contribute to evasion of host defenses, few studies have examined long-term humoral and B-cell responses. Adults with acute-phase skin and soft tissue infections were recruited; blood samples were obtained; and S. aureus isolates, including methicillin-resistant strains, were subjected to genomic sequence analysis. In comparisons of acute-phase sera with convalescent-phase sera, a minority (37.5%) of patients displayed 2-fold or greater increases in antibody titers against three or more S. aureus antigens, whereas nearly half exhibited no changes, despite the presence of toxin genes in most infecting strains. Moreover, enhanced antibody responses waned over time, which could reflect a defect in B-cell memory or long-lived plasma cells. However, memory B cells reactive with a range of S. aureus antigens were prevalent at both acute-phase and convalescent-phase time points. While some memory B cells exhibited toxin-specific binding, those cross-reactive with structurally related leucocidin subunits were dominant across patients, suggesting the targeting of conserved epitopes. Memory B-cell reactivity correlated with serum antibody levels for selected S. aureus exotoxins, suggesting a relationship between the cellular and humoral compartments. Overall, although there was no global defect in the representation of anti-S. aureus memory B cells, there was evidence of restrictions in the range of epitopes recognized, which may suggest potential therapeutic approaches for augmenting host defenses.

The contribution of B-cell memory and long-term antibody responses to host defenses against S. aureus exotoxins remains poorly understood. Our studies confirmed that infection did not commonly lead to enhanced long-term humoral responses. Whereas circulating memory B cells against S. aureus secreted exotoxins were prevalent, they were dominated by cross-reactivity with structurally related leucocidin subunits, consistent with recognition of conserved epitopes. These findings also provide the first evidence of a relationship between the reactivity of antistaphylococcal circulating memory B cells and serum antibody levels. In general, infection was not associated with a global defect in B-cell memory for S. aureus secreted factors, and responses were highly dominated by cross-reactivity to structurally related exotoxins, which arguably may alone be suboptimal in providing host defenses. Our studies illuminate aspects of the S. aureus-host relationship that may better inform strategies for the development of an effective protective vaccine.

Virulence Factor Targeting of the Bacterial Pathogen Staphylococcus aureus for Vaccine and Therapeutics

BACKGROUND

Staphylococcus aureus is a major bacterial pathogen capable of causing a range of infections in humans from gastrointestinal disease, skin and soft tissue infections, to severe outcomes such as sepsis. Staphylococcal infections in humans can be frequent and recurring, with treatments becoming less effective due to the growing persistence of antibiotic resistant S. aureus strains. Due to the prevalence of antibiotic resistance, and the current limitations on antibiotic development, an active and highly promising avenue of research has been to develop strategies to specifically inhibit the activity of virulence factors produced S. aureus as an alternative means to treat disease.

OBJECTIVE

In this review we specifically highlight several major virulence factors produced by S. aureus for which recent advances in antivirulence approaches may hold promise as an alternative means to treating diseases caused by this pathogen. Strategies to inhibit virulence factors can range from small molecule inhibitors, to antibodies, to mutant and toxoid forms of the virulence proteins.

CONCLUSION

The major prevalence of antibiotic resistant strains of S. aureus combined with the lack of new antibiotic discoveries highlight the need for vigorous research into alternative strategies to combat diseases caused by this highly successful pathogen. Current efforts to develop specific antivirulence strategies, vaccine approaches, and alternative therapies for treating severe disease caused by S. aureus have the potential to stem the tide against the limitations that we face in the post-antibiotic era.

Flotillin scaffold activity contributes to type VII secretion system assembly in Staphylococcus aureus

Scaffold proteins are ubiquitous chaperones that promote efficient interactions between partners of multi-enzymatic protein complexes; although they are well studied in eukaryotes, their role in prokaryotic systems is poorly understood. Bacterial membranes have functional membrane microdomains (FMM), a structure homologous to eukaryotic lipid rafts. Similar to their eukaryotic counterparts, bacterial FMM harbor a scaffold protein termed flotillin that is thought to promote interactions between proteins spatially confined to the FMM. Here we used biochemical approaches to define the scaffold activity of the flotillin homolog FloA of the human pathogen Staphylococcus aureus, using assembly of interacting protein partners of the type VII secretion system (T7SS) as a case study. Staphylococcus aureus cells that lacked FloA showed reduced T7SS function, and thus reduced secretion of T7SS-related effectors, probably due to the supporting scaffold activity of flotillin. We found that the presence of flotillin mediates intermolecular interactions of T7SS proteins. We tested several small molecules that interfere with flotillin scaffold activity, which perturbed T7SS activity in vitro and in vivo. Our results suggest that flotillin assists in the assembly of S. aureus membrane components that participate in infection and influences the infective potential of this pathogen.

The recently discovered functional membrane microdomains (FMM) of prokaryotic cells contain a protein homologous to the scaffold protein flotillin found in eukaryotic lipid rafts. It remains to be elucidated whether, like their eukaryotic counterparts, flotillin homolog proteins have a scaffold function in bacteria. Here we show that the Staphylococcus aureus flotillin FloA acts as a scaffold protein, to promote more efficient assembly of membrane-associated protein interacting partners of multi-enzyme complexes. In a case study, we provide biochemical evidence that FloA participates in assembly of the Type VII secretion system and thus contributes to S. aureus infective potential. Targeted dispersion of FMM-related processes using anti-FMM molecules opens up new perspectives for microbial therapies to treat persistent S. aureus infections.

Differential epitope recognition in the immunodominant staphylococcal antigen A of Staphylococcus aureus by mouse versus human IgG antibodies

The immunodominant staphylococcal antigen A (IsaA) is a potential target for active or passive immunization against the important human pathogen Staphylococcus aureus. Consistent with this view, monoclonal antibodies against IsaA were previously shown to be protective against S. aureus infections in mouse models. Further, patients with the genetic blistering disease epidermolysis bullosa (EB) displayed high IsaA-specific IgG levels that could potentially be protective. Yet, mice actively immunized with IsaA were not protected against S. aureus infection. The present study was aimed at explaining these differences in IsaA-specific immune responses. By epitope mapping, we show that the protective human monoclonal antibody (humAb) 1D9 recognizes a conserved 62-residue N-terminal domain of IsaA. The same region of IsaA is recognized by IgGs in EB patient sera. Further, we show by immunofluorescence microscopy that this N-terminal IsaA domain is exposed on the S. aureus cell surface. In contrast to the humAb 1D9 and IgGs from EB patients, the non-protective IgGs from mice immunized with IsaA were shown to predominantly bind the C-terminal domain of IsaA. Altogether, these observations focus attention on the N-terminal region of IsaA as a potential target for future immunization against S. aureus.

The effect of immunoregulation of Streptococcus lactis L16 strain upon Staphylococcus aureus infection

BACKGROUND

Staphylococcus aureus is an important pathogen that causes various infections in medical facilities. However, resistance to multiple drugs has made this infection difficult to manage. Thus, new therapeutic strategies are urgently needed to solve this worldwide public health problem. The Streptococcus lactis L16 strain was isolated from the fermented hot chili sauce. To explore whether it can be used as a protective agent against S. aureus infection, we designed a mouse model of S. aureus infection to evaluate the therapeutic potency of S. lactis. Mice were grouped into pre-(P) and post-(T) S. aureus infection groups following oral administration of S. lactis L16. The protection and treatment effects were assessed by examining body weight, internal organ weight, serum cytokines and intestinal secretory IgA alternations.

RESULT

Oral administration of the S. lactis L16 strain reduced the loss of body weight in mice post-infection and alleviated infection-induced hepatomegaly. In particular, the PL16 group (protection with L16) showed more effective resistance to S. aureus than the TL16 group (treatment with L16). The level of serum cytokine interferon gamma following oral administration of the L16 strain was remarkably increased during infection, as were interleukin-4 levels during convalescence. The probiotic L16 strain induced more sIgA production than S. aureus.

CONCLUSION

Our data suggest that S. lactis L16 is an effective strain with anti-Staphylococcus activity. By regulating the Th1/Th2 response, S. lactis can effectively reduce lesions from infection, indicating its therapeutic potential in overcoming antibiotic resistance in this mouse infection model that mimics infections observed in humans.

Partial Immunoblotting of 2D-Gels: A Novel Method to Identify Post-Translationally Modified Proteins Exemplified for the Myelin Acetylome

Post-translational modifications (PTMs) play a key role in regulating protein function, yet their identification is technically demanding. Here, we present a straightforward workflow to systematically identify post-translationally modified proteins based on two-dimensional gel electrophoresis. Upon colloidal Coomassie staining the proteins are partially transferred, and the investigated PTMs are immunodetected. This strategy allows tracking back the immunopositive antigens to the corresponding spots on the original gel, from which they are excised and mass spectrometrically identified. Candidate proteins are validated on the same membrane by immunodetection using a second fluorescence channel. We exemplify the power of partial immunoblotting with the identification of lysine-acetylated proteins in myelin, the oligodendroglial membrane that insulates neuronal axons. The excellent consistency of the detected fluorescence signals at all levels allows the differential comparison of PTMs across multiple conditions. Beyond PTM screening, our multi-level workflow can be readily adapted to clinical applications such as identifying auto-immune antigens or host-pathogen interactions.