<prompt> CD marker of histiocytosis is ?CD1ACD 1BCD1CCD1D  <response>: Ans. is a i.e., CD1A CD1A is a T cell surface antigen impoant in dendritic cell presentation of glycolipids and lipopeptide antigens. It is used to diagnose Langerhans cell histiocytosis. The presence of Birbeck granules in the cytoplasm of tumor cells is characteristic of Langerhans cell histiocytosis. As Birbeck granules are not seen in all tumor cells by election microscopy the detection of S-100 and CD1a expression by immunohistochemical techniques aids in the diagnosis. Other immunohistochemical markers of Langerhans cell histiocytosis are HLA-DR, Langerin CD 207, and CD 68. 