Cluster of differentiation 74 (CD74) is an important integral membrane protein that serves as a chaperone for MHC class II molecules. CD74, also known as the invariant chain or Ii, is needed for the proper folding and trafficking of MHC class II in antigen presenting cells. CD74 serves as a scaffold for MHC class II assembly. During assembly CD74 blocks the peptide binding cleft of MHC class II to prevent binding of antigenic peptides.
