CD1a is a non polymorphic MHC Class 1 related cell surface glycoprotein, expressed in association with Beta 2 microglobulin. CD1a is expressed by cortical thymocytes, Langerhan's cells and by interdigitating cells. CD1a is also expressed by some malignancies of T cell lineage and in histiocytosis X. Tissue specificity: Expressed on cortical thymocytes, epidermal Langerhans cells, dendritic cells, on certain T-cell leukemias, and in various other tissues.