CYTOPLASMIC TAIL-DEPENDENT LOCALIZATION OF CD1B ANTIGEN-PRESENTING MOLECULES TO MIICS

CD1 proteins have been implicated as antigen-presenting molecules for T cell-mediated immune responses, but their intracellular localization and trafficking remain uncharacterized. CD1b, a member of this family that presents microbial lipid antigens of exogenous origin, was found to localize to endocytic compartments that included the same speciali zed subset of endosomes in which major histocompatibility complex (MHC ) class II molecules are proposed to bind endocytosed antigens. Unlike MHC class II molecules, which traffic to antigen-loading endosomal co mpartments [MHC class II compartments (MIICs)] primarily as a conseque nce of their association with the invariant chain, localization of CD1 b to these compartments was dependent on a tyrosine-based motif in its own cytoplasmic tail.