CD1E, also known as R2 or CD1A, is a 322 amino acid single-pass type I membrane protein that localizes to the lumen of the endoplasmic reticulum, as well as to the golgi apparatus, and contains one Ig-like domain. Expressed in a variety of tissues and on cortical thymocytes, dendritic cells and Langerhans cells, CD1E exists as a heterodimer with beta-2-Microglobulin and is necessary for the presentation of glycolipid antigens on the cell surface. CD1E is subject to post-translational mono-ubiquitination and may also be proteolytically cleaved in endosomes to yield a soluble protein. CD1E is present on the surface of some T-cell leukemias, suggesting a possible role in tumorigenesis.