Characterization of CD1e, a third type of CD1 molecule expressed in dendritic cells

Dendritic cells express several alternatively spliced CD1e mRNAs. These mol ecules encode proteins characterized by the presence of either one, two, or three cu domains and either a 51- or 63-amino acid cytoplasmic domain. Mor eover, mRNAs encoding isoforms lacking the transmembrane domain are observe d. Several of these CD1e isoforms were expressed in transfected cells, and two of them, with three a domains, displayed a particular processing pathwa y. These latter isoforms slowly leave the endoplasmic reticulum due to the presence of atypical dilysine motifs in the cytoplasmic tail. These molecul es are associated with the beta (2)-microglobulin and accumulate in late Go lgi and late endosomal compartments. In the latter compartments, they are c leaved into soluble forms that appear to be stable, In dendritic cells, the se isoforms are mainly located in the Golgi apparatus, and upon maturation they are redistributed to late endosomal compartments. This work demonstrat es the existence of CD1e molecules. As compared with other CD1 molecules, C D1e displays fundamentally different properties and therefore may represent a third type of CD1 molecules.