This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Primary Immunodeficiency, Subject name: Pediatrics
[{'content': 'The commonest 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: Isolated IgA Deficiency: commonest immunodeficiency (1/600) Affected individuals have extremely low levels of both serum and secretory IgA C/F: asymptomatic, recurrent respiratory infections', 'role': 'assistant'}]