The cellular pathway of CD1e in immature and maturing dendritic cells

Dendritic cells (DCs) present antigens to T cells via CD1, HLA class I or class II molecules. During maturation, HLA class II-restricted presentation is optimized. The relocalization of CD1e from Golgi to endosomal compartments during DC maturation suggests also an optimization of the antigen-presentation pathway via CD1 molecules. We here detail the biosynthesis and cellular pathway of CD1e in immature and maturing DCs. Unlike the other CD1 molecules, CD1e was found to reach late endosomes through sorting endosomes, without passing through the plasma membrane in either immature or maturing cells. After induction of DC maturation, CD1e disappeared rapidly from the Golgi and was transiently localized in HLA-DR+ vesicles, while the number of CD1e+/CD1b+ compartments increased for at least 20 h. High-resolution light microscopy showed that, in immature DCs, CD1e+ vesicles were often in close apposition to EEA1+ or HLA-DR+ compartments, while CD1e displayed a nearly exclusive distribution in the lysosomes of mature DCs, a finding corroborated by immunoelectron microscopy. During maturation, CD1e synthesis progressively declined, while the endosomal cleavage of CD1e still occurred. Thus, CD1e displays peculiar properties, suggesting an unexpected role among the family of CD1 antigen-presenting molecules.