<prompt> Which of the following statements characterizes idiotypic determinants?They are found in the crystallizable fragmentFc of immunoglobulinsThey are found on protein antigensThey can be antigenicThey are found in the constant regions of immunoglobulins  <response>: 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. 