Less commonly, SAgs attach to the polymorphic MHC class II β-chain in an interaction mediated by a zinc ion coordination complex between three SAg residues and a highly conserved region of the HLA-DR β chain.[1] The use of a zinc ion in binding leads to a higher affinity interaction.[2] Several staphylococcal SAgs are capable of cross-linking MHC molecules by binding to both the α and β chains.[4][5] This mechanism stimulates cytokine expression and release in antigen presenting cells as well as inducing the production of costimulatory molecules that allow the cell to bind to and activate T cells more effectively.[5]