This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
[{'content': 'The serum concentration of which of the following human IgG subclass is maximum? \nSelect and explain. \nA. IgG1, B. IgG2, C. IgG3, D. IgG4', 'role': 'user'}, {'content': "Answer: A \nExplanation: IgG comprises about 75 to 85% of total serum immunoglobulinThe four IgG subclasses are numbered in order of their level in serumIgG1 is found in greatest amounts and IgG4 the least (Ref: Harrison's 18/e p2036)", 'role': 'assistant'}]