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 most common primary immunodeficiency is: \nSelect and explain. \nA. Common variable immunodeficiency, B. Isolated IgA immunodeficiency, C. Wiskott-Aldrich syndrome, D. AIDS', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Isolated IgA immunodeficiency(Ref: Harrison, 18th/e, p. 2704 and 17th/e, p. 2058)Selective IgA deficiency is the most common primary immunodeficiency, familial (more common), naive B cells are not able to differentiate into IgA producing cells. Along with IgA, IgG2 and IgG4 may also be reduced.", 'role': 'assistant'}]