The exact pa of the antigen that reacts with the immune system is called as -
An epitope, also known as antigenic determinant, is the pa of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. Ref: Ananthanarayan & Panikers textbook of microbiology 9th edition pg:88
Clone
Epitope
Idiotope
Effector
Immunology