The epitope, or antigenic determinant, refers to the specific part of the antigen that is recognized by the paratope. The paratope defines the particular zone of the antibody whose function is to recognize the antigen. Each antigen is determined by its epitopes. In this way, if an antigen's epitopes are characterized as non-self, then the antigen is also assimilated as non-self and triggers an immune response by the organism. Epitopes B and T constitute the two principal types of epitope.