This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Pathology
Birbeck's granule is seen? 
Select and explain. 
A. Granulomatous vasculitis, B. Histocytic necrotizing lymphadenitis, C. Langerhans cells histocytosis, D. Multiple myeloma
C: Langerhans cells histocytosis
Answer: C: Langerhans cells histocytosis 
Explanation: Ans. is 'c' i.e., Langerhan's cells histocytosis Langerhans cell histiocytosis (Histiocytosis-X)* Histocytosis X is characterized by proliferation of Langerhans histiocytes (tissue macrophages). It is subdivided into three categoriesi) Letterer - Siwe syndromeii) Hand -Schuller-Christian diseaseiii) 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 the electron microscope, Birbeck granules have a pentalaminar, rodlike, tubular apperance and sometimes a dilated terminal end (tennis - racket appearance).