Inhibition of staphylococcal enterotoxin A-induced superantigenic and lethal activities by a monoclonal antibody to toxic shock syndrome toxin-1.

Staphylococcal toxic shock syndrome is caused by a family of related superantigens that includes toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxins (SEs) A, B, and C. The cross-inhibitory activity against SEA by a novel anti-TSST-1 monoclonal antibody (MAb), MAb5, which also cross-inhibits SEB-induced superantigenic activities, was investigated. MAb5 blocked SEA binding to human monocytes, cross-neutralized SEA-induced T cell mitogenesis and TNF-alpha secretion in human peripheral blood mononuclear cells, and prevented lethality in mice. Epitope mapping revealed that MAb5 binds to residues SEA(154-161) within the central alpha helix that is structurally highly conserved among TSST-1, SEA, and SEB. The cross-inhibitory activity of MAb5 is likely due to steric hindrance of this conserved motif, although the precise function of this motif shared among related staphylococcal superantigens remains to be further elucidated.