Schematic picture of an MHC-class II molecule and a pepide. Presented is an MHC-class II molecule with the peptide-binding groove containing the peptide-binding pockets P1, P4, P6, and P9. Each pocket binds an anchor residue of a peptide. The properties of the binding pockets define the peptides that can be bound and presented to CD4⁺ T cells. (Figure and legend reprinted from Reipert et al.⁴¹ )