– Mouse HLA class II histocompatibility antigen gamma chain (CD74), is a single-pass type II membrane protein that in humans is encoded by the CD74 gene. It contains 1 thyroglobulin type-1 domain. CD74 Plays a critical role in MHC class II antigen processing by stabilizing peptide-free class II alpha/beta heterodimers in a complex soon after their synthesis and directing transport of the complex from the endoplasmic reticulum to compartments where peptide loading of class II takes place.