This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
[{'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 Extremely low levels of serum & secretory IgA (may be IgG2 & IgG4 too) Defective differentiation of B cells to IgA producing plasma cells CF Mucosal immunity affected Recurrent sinopulmonary infections & diarrhoea When transfused with blood containing IgA may develop fatal anaphylactic reactions', 'role': 'assistant'}]