Antigen

An antigen is a molecule that stimulates an immune response in the body, especially the production of antibodies. Usually, it is a protein or a polysaccharide, but can be any type of molecule, including small molecules (haptens) coupled to a protein (carrier).

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• Immunogen - Any substance that provokes the immune response when introduced into the body. An immunogen is always a macromolecule (protein, polysaccharide). Its ability to provoke the immune response depends on its foreignness to the host, molecular size, chemical composition and heterogeneity (e.g. different amino acids in a protein).
• Tolerogen - An antigen that invokes a specific immune non-responsiveness due to its molecular form. If its molecular form is changed, a tolerogen can become an immunogen.
• Allergen - An allergen is a substance that causes the allergic reaction. It can be ingested, inhaled, injected or comes into contact with skin.

Cells present their antigens to the environment via a histocompatibility molecule. Depending on the antigen presented and the type of the histocompatibility molecule, several types of immune cells can become activated.

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Immune: REDIRECT Immunity (medical)...

Antibodies: REDIRECT antibody...

Protein: A protein (in Greek πρωτεϊνη = first thread) is a complex, high-molecular-weight organic compound that consists of amino acids joined by peptide bonds. Proteins are essential to the structure and function of all living cells and viruses....