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 statements characterizes idiotypic determinants? 
Select and explain. 
A. They are found in the crystallizable fragment(Fc) of immunoglobulins, B. They are found on protein antigens, C. They can be antigenic, D. They are found in the constant regions of immunoglobulins
C: They can be antigenic
Answer: C: They can be antigenic 
Explanation: The idiotype is defined as the specific region of the Fab poion of the Ig molecule to which antigen binds. Antibodies against the idiotype poion of an antibody molecule are called anti-idiotype antibodies. The formation of such antibodies in vivo during a normal B cell antibody response may generate a negative signal to B cells to terminate antibody production. Variable regions (VL and VH) constitute the antibody-binding (Fab) region of the molecule. Within the VL and VH regions are hypervariable regions (extreme sequence variability) that constitute the antigen-binding site unique to each Ig molecule.