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
Prozone phenomenon is due to - 
Select and explain. 
A. Excess antigen, B. Excess antibody, C. Hyperimmune reaction, D. Dispropoiona te antigen-antibody cells
B: Excess antibody
Answer: B: Excess antibody 
Explanation: In an agglutination or precipitation reaction, the zone of relatively high antibody concentrations within which no reaction occurs. As the antibody concentration is lowered below the prozone, the reaction occurs. This phenomenon may be due simply to antibody excess or it may be due to blocking antibody or to nonspecific inhibitors in serum. Ref: Ananthanarayan & Parker's textbook of microbiology 9th edition pg:105