How T cells see the HC gp-39(263–275) epitope bound to HLA-DRB1*0401. (a) Structural model of the HLA-DR4(B1*0401)/HC gp-39(263–275) complex. Blue, α-chain; purple, β-chain. (b) Model of what the T-cell receptors 'see' when contacting the HLA-DR4(B1*0401)/HC gp-39(263–275) complex. A close up of the MHC surface representation is shown. Peptide residues are coloured by atom type if they are important in the contact, and grey if they are not (the sequence RSFTLASSETGVG is shown with the p1 anchor in bold; underlined residues are primary TCR contacts). MHC β-chain residues that might influence hybridoma activation are coloured orange. Molecular graphics created with YASARA  and PovRay .