Abstract
Staphylococcal enterotoxin B (SEB) is one of the most potent Staphylococcus aureus exotoxins (SEs). Due to its conserved sequence and stable structure, SEB might be a good candidate antigen for MRSA vaccines. Although cellular immune responses to SEB are well-characterized, much less is known regarding SEB-specific humoral immune responses, particularly regarding detailed epitope mapping. In this study, we utilized a recombinant nontoxic mutant of SEB (rSEB) and an AlPO4 adjuvant to immunize BALB/c mice and confirmed that rSEB can induce a high antibody level and effective immune protection against MRSA infection. Next, the antisera of immunized mice were collected, and linear B cell epitopes within SEB were finely mapped using a series of overlapping synthetic peptides. Three immunodominant B cell epitopes of SEB were screened by ELISA, including a novel epitope, SEB205-222, and two known epitopes, SEB97–114 and SEB247-261. Using truncated peptides, an ELISA was performed with peptide-KLH antisera, and the core sequence of the three immunodominant B cell epitopes were verified as SEB97-112, SEB207-222, and SEB247-257. In vitro, all of the immunodominant epitope-specific antisera (anti-SEB97-112, anti-SEB207-222 and anti-SEB247-257) were observed to inhibit SEB-induced T cell mitogenesis and cytokine production from splenic lymphocytes of BALB/c mice. The homology analysis indicated that SEB97–112 and SEB207-222 were well-conserved among different Staphylococcus aureus strains. The 3D crystal structure of SEB indicated that SEB97–112 was in the loop region inside SEB, whereas SEB207-222 and SEB247-257 were in the β-slice region outside SEB. In summary, the fine-mapping of linear B-cell epitopes of the SEB antigen in this study will be useful to understand anti-SEB immunity against MRSA infection further and will be helpful to optimize MRSA vaccine designs that are based on the SEB antigen.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) infections cause a high mortality rate in the United States [1], China [2] and Japan [3]
80% of mice that were immunized with recombinant nontoxic mutant of SEB (rSEB) plus AlPO4 adjuvant survived without clinical signs, and the survival rate of these mice was higher than that in the AlPO4 adjuvant alone group (20%) and higher than that in the PBS group (Figure 1A)
The results showed that the vaccination of rSEB plus AlPO4 adjuvant induced a significant antibody response that was specific to the native Staphylococcal enterotoxin B (SEB) in mice
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) infections cause a high mortality rate in the United States [1], China [2] and Japan [3]. MRSA infections have been the leading cause of death by a single infectious agent in the USA, exceeding deaths that are caused by HIV/AIDS [4]. No effective MRSA vaccine has been successfully developed far [5]. Staphylococcal enterotoxin B (SEB) is one of the most common and potent exotoxins of S. aureus [8] and is considered to be a primary causative agent of staphylococcal TSS(Toxic Shock Syndrome) [9,10]. Many researchers have generated monoclonal antibodies against SEB that could prevent toxic shock syndrome that is induced by S
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