Introduction
T cells typically recognize antigens presented on members of the MHC protein family via highly diverse heterodimeric T cell receptors (TCRs) expressed at their surface . These antigens are commonly short peptide fragments of eight or more residues, the presentation of which is dictated in large part by the structural preferences of the MHC allele. Lipid, metabolite and oligosaccharide T cell antigens have also been reported. TCRs typically engage antigen–MHC complexes via one or more of their six complementarity-determining loops (CDRs), three contributed by each chain of the TCR dimer.
