A super-antigen is a bacterial product that

Superantigens Activate large populations of T cells that express paicular subsets of the T cell receptor b protein, causing massive cytokine release and subsequent host reactions. Conventional antigens bind to MHC class I or II molecules in the groove of the ab heterodimer and bind to T cells the V regions of the TCR-a and -b chains. In contrast, superantigens bind directly to the lateral poion of the TCR-b chain and MHC class II b chain T cell superantigens include staphylococcal enterotoxins and other bacterial products.