This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
CD marker of histiocytosis is ? 
Select and explain. 
A. CD1A, B. CD 1B, C. CD1C, D. CD1D
A: CD1A
Answer: A: CD1A 
Explanation: 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.