Figure 2

Role of MTP in the biosynthesis of CD1 proteins: MTP transfers endogenous lipids to newly synthesized CD1 proteins in the ER (a). CD1 proteins also associate with β2-microglobulin (β2 m) before entering the secretory pathway (b). In the absence of MTP, group 1 CD1 proteins are subjected to proteasomal degradation (c). Group 2 CD1 proteins, on the other hand, are still transported to the plasma membrane in the absence of MTP. From the plasma membrane, CD1 proteins are constitutively internalized via clathrin-mediated endocytosis (d) and reach endosomal recycling compartment. In this compartment, saposins remove endogenous lipids and load different lipid antigens onto CD1 proteins (e). CD1 molecules with foreign lipids are recycled back to the plasma membrane (f), where they present their lipid antigens to restricted population of T cells.