This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'The exact pa of the antigen that reacts with the immune system is called as - \nSelect and explain. \nA. Clone, B. Epitope, C. Idiotope, D. Effector', 'role': 'user'}, {'content': 'Answer: B \nExplanation: An epitope, also known as antigenic determinant, is the pa of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. Ref: Ananthanarayan & Panikers textbook of microbiology 9th edition pg:88', 'role': 'assistant'}]