QL9

QL9 (QLSPFPFDL) is a high-affinity alloantigen for the 2C T cell receptor (TCR). IC50 & Target:TCR^[1] In Vitro: Mouse T cell clone 2C recognizes two different major histocompatibility (MHC) ligands, the self MHC K^b and the allogeneic MHC L^d. Two distinct peptides, SIY (SIYRYYGL) and QL9 (QLSPFPFDL), act as strong and specific agonists when bind to K^b and L^d, respectively. QL9 binding to MHC L^d is influenced by the majority of peptide side chains, distributed across the entire length of the peptide. Findings with both systems, but QL9-L^d in particular, suggest that many single-residue substitutions, introduced into peptides to improve their binding to MHC and thus their vaccine potential, could impair T cell reactivity due to their dual impact on TCR binding. T cell activation assays are performed to measure effects of peptide SIY and QL9 residues on T cell function^[2].