An<unk>  is any substance that generates B-cell (humoral/antibody) and/or T-cell (cellular) adaptive immune responses upon exposure to a host organism.<unk> s that generate antibodies are called antigens ("antibody-generating").<unk> s that generate antibodies are directly bound by host antibodies and lead to the selective expansion of antigen-specific B-cells.<unk> s that generate T-cells are indirectly bound by host T-cells after processing and presentation by host antigen-presenting cells. An<unk>  can be defined as a complete antigen which is composed of the macromolecular carrier and epitopes (determinants) that can induce immune response. An explicit example is a hapten. Haptens are low-molecular-weight compounds that may be bound by antibodies, but cannot elicit an immune response. Consequently, the haptens themselves are nonimmunogenic and they cannot evoke an immune response until they bind with a larger carrier<unk> ic molecule. The hapten-carrier complex, unlike free hapten, can act as an<unk>  and can induce an immune response. Until 1959, the terms<unk>  and antigen were not distinguished.
Immunogen
Antigen
Allergen
Chemical substance
Biological agent
Bioactive compound
Nutrient
Biomaterial