Asingle antigen molecule may be composed of many individual
t-cell receptors
b-cell receptors
mhc ii
epitopes

Epitopes.

Explanation:

Antigen: Antigens are foreign proteins that enter the host body through an infection. Antigens are generally high molecular weight proteins or polysaccharides. Viruses and bacteria contain antigen on their surface or inside the body.

Epitope: Epitope is the molecular region on the surface of the antigen which interacts with the antibody binding site on the antigen. Epitopes are capable of stimulating an immune response so, these are also known as antigenic determinants. Binding between the receptor and epitopes occurs when they both fit together like a puzzle, that event is necessary to activate B-cell production of antibodies.