This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which of the subclass of IgG has the maximum serum concentration? 
Select and explain. 
A. IgG1, B. IgG2, C. IgG3, D. IgG4
A: IgG1
Answer: A: IgG1 
Explanation: IgG is the most abundant of the immunoglobulins. It has two heavy and two light chains linked by disulfide bonds. 4 subclasses of IgG are present, each differ from each other based on the amino acid sequence. Each of the 4 subclasses has unique epitopes. The subclasses of IgG are present in different amounts with IgG1>IgG2>IgG3>IgG4. IgG1 subclass has the maximum serum concentration. Ref: Infection, Resistance and Immunity By Julius P. Kreie, 2nd Edition, Page 118