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: Physiology
The serum concentration in which of the following human IgG subclasses is maximum? 
Select and explain. 
A. IgG1, B. IgG2, C. IgG3, D. IgG4
A: IgG1
Answer: A: IgG1 
Explanation: IgG 1 - 65%, IgG2- 23%. IgG3 -8% IgG4 - 4%