CD1c, and Class II Human leukocyte antigens. Langerhans cells A subset of cells differentiates into Langerhans cells; this maturation occurs in the squamous epithelium, lymph nodes, spleen, and bronchiolar epithelium. Langerhans cells are antigen-presenting cells but have undergone further differentiation. Skin Langerhans cells express CD1a, as do cortical thymocytes (cells of the cortex of the thymus gland). They also express S-100, and their cytoplasm contains tennis-racket like ultra-structural inclusions called Birbeck granules. Clinical significance Histiocytoses describe neoplasias wherein the proliferative cell is the histiocyte. The most common histiocyte disorders are Langerhans' cell histiocytosis and haemophagocytic lymphohistiocytosis. See also Histiocytosis References Cell biology Mononuclear phagocytes