<prompt> The exact part of the antigen that reacts with the immune system is called as:CloneEpitopeIdiotopeEffector  <response>: Ans. is b i.e., EpitopeRef: Ananthanarayan, 9the, p. 88 and 7the, p. 81; Harrison, 18the, p. 2673 and 17the, p. 2036 The part of the antibody or T cell receptor that interact with the epitope. 