This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Pathology
[{'content': "Birbeck granules in the cytoplasm are seen in- \nSelect and explain. \nA. Mast cells, B. Langerhan's cells, C. Thrombocytes, D. Myelocytes", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Birbeck granules, also known as Birbeck bodies, are rod shaped or "tennis-racket" cytoplasmic organelles with a central linear density and a striated appearance. First described in 1961 (where they were simply termed "characteristic granules"), they are solely found in Langerhans cells. Although pa of normal Langerhans cell histology, they also provide a mechanism to differentiate Langerhans cell histiocytoses (which are a group of rare conditions collectively known as histiocytoses) from proliferative disorders caused by other cell lines. Formation is induced by langerin.', 'role': 'assistant'}]