Inhibition of Staphylococcal Enterotoxin B-Induced Lymphocyte Proliferation and Tumor Necrosis Factor Alpha Secretion by MAb5, an Anti-Toxic Shock Syndrome Toxin 1 Monoclonal Antibody

Abstract

Toxic shock syndrome (TSS) is primarily caused by toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin B (SEB). These toxins belong to a family of pyrogenic toxin superantigens (PTSAgs) produced by Staphylococcus aureus and exhibit several shared biological properties, including the induction of massive cytokine release and V␤-specific T-cell proliferation. The crystal structures of most PTSAgs are now published, and they demonstrate a striking similarity in conformational architecture even though their primary protein sequences are different. Despite these structural and immunobiological similarities, no cross-reactivity between TSST-1 and other PTSAgs has been demonstrated in serological or neutralization assays. Our laboratory has developed a neutralizing murine anti-TSST-1 monoclonal antibody (MAb5) which displayed cross-reactivity with SEB by enzyme-linked immunosorbent assay. The aim of the present study was to evaluate whether MAb5 can also cross-neutralize SEB-induced superantigenic activities in vitro. MAb5 was found to partially inhibit SEB-induced T-cell mitogenesis (63%) and tumor necrosis factor alpha (TNF-␣) secretion (70%) in human peripheral blood mononuclear cells (PBMC) in a dose-dependent manner, while an isotypic anti-TSST-1 monoclonal antibody showed no effect. Epitope mapping revealed that MAb5 bound to TSST-1 residues 47 to 56 ( 47 FPSPYYSPAF 56 ) and to SEB residues 83 to 92 ( 83 DVFGANYYYQ 92 ), sequences that located in different regions of these toxins and are structurally dissimilar. SEB peptide 83 DVFG-ANYYYQ 92 was synthesized and found to also inhibit SEB-induced mitogenesis and TNF-␣ secretion in human PBMC. Our results demonstrate for the first time that MAb5 binds to different epitopes on TSST-1 and SEB that appear functionally important in inducing T-cell mitogenesis and TNF-␣ secretion in vitro.

Inhibition of Staphylococcal Enterotoxin A–Induced Superantigenic and Lethal Activities by a Monoclonal Antibody to Toxic Shock Syndrome Toxin–1

“…Furthermore, Bohach et al [28] found cross-neutralization of SEB and streptococcal pyrogenic exotoxin A induced mitogenic effect by MAbs against SEC1. We reported elsewhere that a neutralizing MAb raised against TSST-1 (MAb5) also cross-inhibited SEB-induced superantigenic activity in vitro [32]. In the present study, we demonstrated that this anti-TSST-1 MAb5 also cross-inhibits SEA-induced mitogenic activity and TNF-a secretion in vitro and protects against SEA-induced lethality in the mouse model.…”

“…We [31] and others [43,44] previously showed this region to mediate TSST-1 binding to MHC class II molecules. In the case of SEB, the cross-inhibitory effect of MAb5 appears to be directed at SEB(83-92) ( 83 DVFGANYYYQ 92 ), which forms a b-sheet within domain B, and is implicated in both MHC class II binding and TCR engagement (figure 6C) [32]. In the case of SEA in the current study, the cross-inhibitory activity of MAb5 is directed at SEA(154-161) ( 154 ELDLQARR 161 ) within the central a helix of domain A ( figure 6A).…”

“…MAb5 also demonstrated significant cross-reactivity with SEA by ELISA, which suggests the presence of cross-reactive epitopes on TSST-1 and SEA. We also showed that MAb5 also cross-inhibited SEB-induced superantigenic activity in vitro [32]. The aim of the current study, therefore, was to examine the ability of MAb5 to cross-inhibit SEA-induced superantigenic and lethal activities both in vitro and in vivo.…”

TCR recognition of peptide/MHC class II complexes and superantigens

“…Intravenously-administered pooled human immunoglobulin (IVIG) has been used with some success, but its supply is limited and its effectiveness is variable [61,62]. Mouse monoclonal antibodies have been generated against SEB [63,64], but have not been humanized for clinical use. A potentially more general anti-inflammatory agent, a recombinant cell-penetrating form of the suppressor of cytokine signaling 3 (SOCS3) has exhibited some efficacy in protecting mice challenged with lethal doses of SEB [65].…”

Potent Neutralization of Staphylococcal Enterotoxin B by Synergistic Action of Chimeric Antibodies

“…However, rapid in vivo turnover of SEB blocking agents can be avoided by use of antibodies well matched to the host's FcRn, a receptor responsible for protecting IgG from proteolysis and hence endowing it with a long half-life (24). The use of monoclonal antibodies to neutralize the effects of SEB was first demonstrated by the pioneering studies of Hamad et al (17) and later by the work of Pang et al (39). Furthermore, using genes encoding the V regions of monoclonal antibodies derived in nonhuman species, it has been possible to engineer a number of useful chimeric antibodies that manifest relatively long half-lives and low immunogenicity in humans (8).…”