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 following immunoglobulins has the highest mean serum concentration in humans? 
Select and explain. 
A. IgA, B. IgD, C. IgG, D. IgM
C: IgG
Answer: C: IgG 
Explanation: IgG is the most abundant class of immunoglobulins in the serum, comprising about 80% of the total serum immunoglobulin.
There are four IgG subclasses IgG1, IgG2, IgG3, and IgG4—so numbered according to their decreasing concentrations in serum.

Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page:96