A 3 year old female child presented with skinpapules. Which of the following is a marker of Langerhan's cell histiocytosis?

CD la Histiocytosis is a disorder of the mononuclear phagocytic system. Mononuclear phagocytic system consists of monoblasts, promonocytes, monocytes and tissue macrophages, Macrophages are transformed monocytes i.e. monocytes present in the tissues. Moncytes emigrate continuously from peripheral blood into the tissues. Histiocyte The term histiocyte is synonymous with macrophage. In diseases of mononuclear phagocytic system the terms histiocyte and histiocytosis are used. Langern cell histiocytosis Langerhans cell is macrophage and plays impoant role in immunity. It processes antigen and present it to T cells. Langerhans cells histiocytosis (LCH) is a clonal histiocytosis and the lesions are characterized by the presence of Langerhans cells, eosinophils and Lymphocytes in a variable number. The various features of langerhans cells are : Presence of Birbeck granules (E/M - HX bodies) Presence of enzymes like - a Naphthyl acetate esterase - a Naplahyl butyrate esterase - Acid phosphatase Markers like - S-I00 positivity - CD-la positivity' - HCA-DR expression