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
The serum concentration of which of the following human IgG subclass is maximum? 
Select and explain. 
A. IgG1, B. IgG2, C. IgG3, D. IgG4
A: IgG1
Answer: A: IgG1 
Explanation: 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)