<prompt> Which of the following is not a type of langerhans cell histiocytosis?Hand Schuller Christian diseaseEosinophilic granulomaLetter-siwe syndromeTones syndrome  <response>: Ans. is d. i.e., Torres syndrome Langerhans cell histiocvtosis Histiocytosis X Histiocytosis X is characterized by proliferation of Langerhans histiocytes tissue macrophages. It is Subdivided into three Categories:- Letterer-siwe syndrome Hand-Schuller-Christian disease Eosinophilic granuloma. Tumor cells in each are derived from dendritic cells and express S-100, CD la and HLA-DR. The presence of Birbeck granules in the cytoplasm is characteristic. Under electron microscope, Birbeck granules have a pentalaminar, rod like, tubular appearance and sometimes a dilated terminal end tennis-rachet appearance. 