CD1a is a non-polymorphic, MHC class I–relatedglycoprotein (45–55 kDa) expressed in association with β2-microglobulin. It is found in cortical thymocytes,Langerhans cells, interdigitating dendritic cells, and rareantigen-presenting cells of lymph nodes. CD1a positivityhas been described in Langerhans cell histiocytosis and insubsets of pre-T lymphoblastic lymphoma/leukemia.In research, CD1a serves as a useful marker to studyantigen-presenting cells and immune-related pathologies.