Superantigen bacterial toxins: state of the art

Sup/erantigens (SAgs) are viral and bacterial proteins exhibiting a highly potent polyclonal lymphocyte-proliferating activity for CD4(+), CD8(+) and sometimes gamma delta (+) T cells of human and (or) various animal species. Unlike conventional antigens, SAgs bind as unprocessed proteins to invaria nt regions of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) and to particular motifs of the variable region of the beta chain (V beta) of T-cell receptor (TcR) out side the antigen-binding groove. As a consequence, SAgs stimulate at nano-t o picogram concentrations up to 10 to 30% of host T-cell repertoire while o nly one in 10(5)-10(6) T cells (0.01-0.0001%) are activated upon convention al antigenic peptide binding to TcR. SAg activation of an unusually high pe rcentage of T lymphocytes initiates massive release of pro-inflammatory and other cytokines which play a pivotal role in the pathogenesis of the disea ses provoked by SAg-producing microorganisms. We briefly describe in this r eview the molecular and biological properties of the bacterial superantigen toxins and mitogens identified in the past decade. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.