Abstract
Some Staphylococcus aureus isolates produced toxic shock syndrome toxin-1 (TSST-1) which is a pyrogenic toxin superantigen (PTSAg). The toxin activates a large fraction of peripheral blood T lymphocytes causing the cells to proliferate and release massive amounts of pro-inflammatory cytokines leading to a life-threatening multisystem disorder: toxic shock syndrome (TSS). PTSAg-mediated-T cell stimulation circumvents the conventional antigenic peptide presentation to T cell receptor (TCR) by the antigen-presenting cell (APC). Instead, intact PTSAg binds directly to MHC-II molecule outside peptide binding cleft and simultaneously cross-links TCR-Vβ region. Currently, there is neither specific TSS treatment nor drug that directly inactivates TSST-1. In this study, human single chain antibodies (HuscFvs) that bound to and neutralized bioactivities of the TSST-1 were generated using phage display technology. Three E. coli clones transfected with TSST-1-bound phages fished-out from the human scFv library using recombinant TSST-1 as bait expressed TSST-1-bound-HuscFvs that inhibited the TSST-1-mediated T cell activation and pro-inflammatory cytokine gene expressions and productions.Computerized simulation, verified by mutations of the residues of HuscFv complementarity determining regions (CDRs),predicted to involve in target binding indicated that the HuscFvs formed interface contact with the toxin residues important for immunopathogenesis. The HuscFvs have high potential for future therapeutic application.
Highlights
Superantigens (SAgs) are proteins produced by some bacterial and viral strains that mediate T cell activation by bypassing the conventional peptide-MHC-II presentation to T cell receptor (TCR) [1].Instead, intact SAgs bind directly to MHC-II molecules on the antigen presenting cells (APC)and simultaneously cross-link TCR-Vβ domains shared by about 5%–20% of circulating CD4+Toxins 2017, 9, 50; doi:10.3390/toxins9020050 www.mdpi.com/journal/toxinsToxins 2017, 9, 50 and CD8+ T lymphocytes [1,2]
E. coli grown under 1 mM isopropyl β-D-1-thiogalactopyranoside (IPTG) induction, 1.46 grams of purified recombinant protein was obtained
Pyrogenicity of the IL-1β, IL-6, and TNFαgene expressions, respectively, in the human PBMCs after stimulation with Recombinant TSST-1 (rTSST-1) was not concentration dependent which was conformed to the results reported previously rTSST-1 and PHA in comparison with non-stimulated cells
Summary
Superantigens (SAgs) are proteins produced by some bacterial and viral strains that mediate T cell activation by bypassing the conventional peptide-MHC-II presentation to T cell receptor (TCR) [1]. Intact (unprocessed) SAgs bind directly to MHC-II molecules on the antigen presenting cells (APC)and simultaneously cross-link TCR-Vβ domains shared by about 5%–20% of circulating CD4+. Staphylococcus aureus secretes several pyrogenic toxin superantigens (PTSAgs) including toxic shock syndrome toxin-1 (TSST-1) and many enterotoxins [1,7]. Symptom severity of TSS was mitigated in a rabbit model after giving a mouse monoclonal antibody that neutralized TSST-1 activities [25]. Human monoclonal single chain antibodies (HuscFvs) that bound to functionally important residues of TSST-1 were produced by phage display technology. The human scFvs have high potential for testing further as a safe, direct acting anti-TSST-1 remedy
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