Superantigen-Mediated Lethal Shock: The Functional State of Ligand-Reactive T Cells
A group of bacterial and viral proteins has been termed superantigens (SAg) because of their unique mechanisms to interact with antigen-presenting cells (APC) and T lymphocytes (Herman et al. 1991a; Marrack and Kappler 1990; Herrmann and MacDonald 1991; Acha-Orbea et al. 1993). SAg are comprised of bacterial exoproducts including the staphylococcal enterotoxins, proteins encoded by viral genomes, and retroviral products such as those of open reading frame region encoded SAg of mouse mammary tumor viruses (Table 1 ; Mac-Donald et al. 1988; Marrack et al. 1991,1993; Janeway et al. 1989; Acha-Orbea et al. 1993). All SAg share the distinctive ability to bind to MHC class II molecules as intact molecules, thus bypassing rate-limiting steps during normal antigen processing, including antigen uptake, antigen degradation, and internal binding as peptide fragment to the antigen-presenting groove of class II MHC molecules of APC (Carlsson et al. 1988; Mollick et al. 1989; Fleischer and Schrezenmeier 1988; Torres et al. 1993; Thibodeau et al. 1994; Mottershead et al, 1995). SAg bind directly to regions of the class II molecule that are outside the physiological MHC haplotype-restricted antigen-binding groove (Fig. 1; Dellabona et al. 1990; Herman et al. 1991b; Jardetzky et al. 1994). The SAg binding region seems to be conserved within various MHC haplotypes of mammalian species since SAg bind to murine and rat as well as to human class II molecules (Herrmann and MacDonald 1991; Fraser 1989).
KeywordsMouse Mammary Tumor Virus Staphylococcal Enterotoxin Clonal Deletion Cell Shock Lethal Shock
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