Abstract
Resolution of the structure of the T cell receptor (TCR) bound to a complex between an MHC class I molecule and a peptide of processed antigen sheds new light on the molecular complexities of this interaction. Now, in a Perspective, Ian Wilson discusses new work ( Reinherz et al.) that reveals the structure of TCR bound to an MHC class II-peptide complex and compares and contrasts the two classes of structure.