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: Microbiology
The serum concentration of 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 is the major class of immunoglobulin present in the serum. The IgG molecule consists of two L chains and two H chains (H2L2). There are four subclasses of IgG: IgG1, IgG2, IgG3, and IgG4. Each subtype contains a distinct but related H chain and each differs somewhat regarding their biological activities. IgG1 represents 65% of the total IgG.IgG2- 23%, IgG3 -8% and IgG4 - 4%Reference: Jawetz, Melnick, & Adelberg's Medical Microbiology; 27th edition; Chapter 8; Immunology