Identification of CD4+ T-cell epitopes on iron-regulated surface determinant B of Staphylococcus aureus

Evasion of Immunological Memory by S. aureus Infection: Implications for Vaccine Design

Recurrent S. aureus infections are common, suggesting that natural immune responses are not protective. All candidate vaccines tested thus far have failed to protect against S. aureus infections, highlighting an urgent need to better understand the mechanisms by which the bacterium interacts with the host immune system to evade or prevent protective immunity. Although there is evidence in murine models that both cellular and humoral immune responses are important for protection against S. aureus, human studies suggest that T cells are critical in determining susceptibility to infection. This review will use an “anatomic” approach to systematically outline the steps necessary in generating a T cell-mediated immune response against S. aureus. Through the processes of bacterial uptake by antigen presenting cells, processing and presentation of antigens to T cells, and differentiation and proliferation of memory and effector T cell subsets, the ability of S. aureus to evade or inhibit each step of the T-cell mediated response will be reviewed. We hypothesize that these interactions result in the redirection of immune responses away from protective antigens, thereby precluding the establishment of “natural” memory and potentially inhibiting the efficacy of vaccination. It is anticipated that this approach will reveal important implications for future design of vaccines to prevent these infections.

PilVax, a novel Lactococcus lactis-based mucosal vaccine platform, stimulates systemic and mucosal immune responses to Staphylococcus aureus

Most pathogens initiate infection via the mucosa, therefore delivery of vaccines directly to the mucosa is likely to be advantageous for stimulating protective immunity at the site of entry. PilVax is a novel mucosal vaccine platform that harnesses Lactococcus lactis bacteria engineered to stably express multiple copies of vaccine peptide antigens within pili, hair-like structures which extend from the cell wall. This strategy elicited systemic and mucosal antibody responses to a model antigen after intranasal immunization, but has not been tested for its capacity to stimulate protective mucosal immunity. A well-characterized linear B-cell epitope, D3_(22-33) , from the fibronectin-binding protein A of Staphylococcus aureus was successfully introduced into PilVax and delivered intranasally to mice. Specific antipeptide immunoglobulin (Ig) G and IgA antibodies were detected in the serum and respiratory mucosa of vaccinated mice. Responses to the major pilus backbone protein Spy0128 were also assessed; robust antibody responses to this antigen were generated both systemically and in the respiratory and intestinal mucosa. Mice were challenged intranasally with the mouse-adapted S. aureus JSNZ strain and the S. aureus load quantified 7 days after challenge. Unexpectedly, exposure to PilVax, irrespective of the presence of the peptide, resulted in a significant reduction in S. aureus load in both the intestine and nasal mucosa (both P < 0.05) when compared with unvaccinated control mice. The mechanism(s) of protection are unclear, but merit further investigation to determine whether PilVax is a suitable platform for delivery of vaccine candidate antigens to the mucosa.

Identification of CD4+ T cell epitopes on glyceraldehyde-3-phosphate dehydrogenase-C of Staphylococcus aureus in Babl/c mice

Glyceraldehyde-3-phosphate dehydrogenase-C (GapC) is a highly conserved surface protein of Staphylococcus aureus, with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, which represents an excellent vaccine candidate antigen. It can induce protective immune responses to S. aureus infections. However, CD4⁺ T cell epitopes of GapC that induce CD4⁺ T cell immune responses are currently unclear. In this study, we used bioinformatics prediction algorithms to predict CD4⁺ T cell epitopes of GapC. Ten peptides were synthesized to investigate the candidate epitopes. Our results showed that the peptides, G4 (GapC _104-123) and G10 (GapC _314-333) were able to induce proliferation of CD4⁺ T cells and secrete high levels of interferon (IFN)-γ, respectively. In addition, they significantly reduced bacterial loads in tissue and induced immunoprotective effects. It is suggested that G4 and G10 are Th1-type epitopes of S. aureus GapC. This study provides the potential development of the design of epitope-based vaccine against S. aureus.

Gene synthesizing, expression and immunogenicity characterization of recombinant translation elongation factor 2 from Dermatophagoides farinae

House dust mite (HDM) hypersensitivity increasingly affects millions of individuals worldwide. Although numerous major allergens produced by HDM species have been characterized, some of the less potent allergens remain to be studied. The present study aimed to obtain the recombinant allergen of Translation Elongation Factor 2 (TEF 2) from the HDM Dermatophagoides farinae by synthesizing, and then expressing the recombinant TEF 2 to identify its immunogenicity. In the present study, the D. farinae TEF 2 (Der f TEF 2) was synthesized, expressed and purified. The molecular characteristics of Der f TEF 2 were analyzed using bioinformatics approaches. The recombinant protein was purified via affinity chromatography, and the allergenicity was assessed using immunoblotting, ELISAs and skin prick tests. The gene for TEF 2 consists of 2,535 bp and encodes an 844‑amino acid protein. A positive response to recombinant Der f TEF 2 was detected in 16.2% of 37 patients with HDM allergies using skin prick tests. In addition, the immunoblotting indicated that the protein showed a high ability to bind serum IgE from patients allergic to HDMs, and that the recombinant TEF 2 was highly immunogenic. Bioinformatics analysis predicted 17 peptides as B cell epitopes (amino acids 29‑35, 55‑64, 92‑99, 173‑200, 259‑272, 311‑318, 360‑365, 388‑395, 422‑428, 496‑502, 512‑518, 567‑572, 580‑586, 602‑617, 785‑790, 811‑817 and 827‑836) and 14 peptides as T cell epitopes (amino acids 1‑15, 65‑79, 120‑134, 144‑159, 236‑250, 275‑289, 404‑418, 426‑440, 463‑477, 510‑524, 644‑658, 684‑698, 716‑730 and 816‑830). The software DNAStar predicted the secondary structure of TEF 2, and showed that 27 α‑helices and five β‑sheets were found in the protein. In conclusion, the present study cloned and expressed the Der f TEF 2 gene, and the recombinant protein exhibited immunogenicity, providing a theoretical bases, and references, for the diagnosis and treatment of allergic disease.

Identification and characterization of CD4+ T cell epitopes on manganese transport protein C of Staphylococcus aureus

Manganese transport protein C (MntC) of Staphylococcus aureus represents an excellent vaccine-candidate antigen. The important role of CD4⁺ T cells in effective immunity against S. aureus infection was shown; however, CD4⁺ T cell-specific epitopes on S. aureus MntC have not been well identified. Here, we used bioinformatics prediction algorithms to evaluate and identify nine candidate epitopes within MntC. Our results showed that peptide M8 emulsified in Freund's adjuvant induced a much higher cell-proliferation rate as compared with controls. Additionally, CD4⁺ T cells stimulated with peptide M8 secreted significantly higher levels of interferon-γ and interleukin-17A. These results suggested that peptide M8 represented an H-2d (I-E)-restricted Th17-specific epitope.