Several types of proteins are implicated in the regulation of class Ia MHC assembly, including: 1) TAP1/TAP2 transporters, which translocate peptides derived from naturally processed endogenous proteins from the cytosol into the ER and which are necessary for expression of "peptide-filled" class Ia Ags, and 2) calnexin, a chaperone protein, which was proposed to retain unassembled class Ia chains in the ER.     ///    "In our study, we examined if the expression of class Ib Qa-2 molecules depends on the TAP1/TAP2 peptide delivery system. "