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
Immunoglobulin isotype class switching is determined by - 
Select and explain. 
A. Constant region of light chain, B. Constant region of heavy chain, C. Variable region of light chain, D. Variable region of heavy chain
B: Constant region of heavy chain
Answer: B: Constant region of heavy chain 
Explanation: Antibody genes also re-organize in a process called class switching that changes the one type of heavy chain Fc fragment to another, creating a different isotype of the antibody that retains the antigen specific variable region Ref: Ananthanarayan & Parkers textbook of microbiology 9th edition pg: 96