a common sequence of amino acids in residues 70–74 in the HLA-DRB1 chains, found in alleles associated with rheumatoid arthritis. It is one of two variations: glutamine[Q]-lysine[K]-arginine[R]-alanine[A]-alanine[A] or QRRAA. These susceptibility cassettes are found in many different DRB1 alleles. The α and β chains that form these antigen-presenting molecules have a configuration not unlike a trough or rain gutter; antigens are bound by sequences of amino acids in a pocket along the bottom and sides of the trough or cavity, and this complex forms a heterotrimer with the T-cell receptor on CD4+ cells.
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Examples: glitazone, GI cocktail, etc.