To co-localise with peptide:MHC class II to guide it to the surface of the antigen presenting cell

To co-localise and bind to peptides in the endosome to guide their loading into the MHC class II binding cleft

To stabilise the MHC class II structure during the generation of the MHC class II β chain (prior to peptide loading)

To prevent peptides from intracellular proteins being loaded into MHC class II