Antigens

Definition

Antigens are molecules or molecular structures that can be recognized by the immune system, specifically by antibodies, B cells, or T cells. They trigger an immune response when detected in the body.

5 Must Know Facts For Your Next Test

1. Antigens are typically proteins or polysaccharides found on the surface of pathogens like bacteria and viruses.
2. Each antigen has distinct regions called epitopes that are recognized by specific antibodies.
3. Self-antigens are normal molecules of the host's body, whereas non-self antigens originate from external sources like pathogens.
4. The immune system uses antigen presentation to detect and respond to foreign antigens via MHC (Major Histocompatibility Complex) molecules.
5. Vaccines work by introducing a harmless form of an antigen to stimulate an adaptive immune response without causing disease.

Review Questions

• What types of molecules typically act as antigens?
• How do epitopes relate to antigens and antibodies?
• What role do MHC molecules play in antigen recognition?

Related terms

Antibody:

A protein produced by B cells that binds to a specific epitope on an antigen.

Epitope:

The specific part of an antigen that is recognized and bound by an antibody or T cell receptor.

MHC (Major Histocompatibility Complex): A set of cell surface proteins essential for the acquired immune system to recognize foreign molecules in vertebrates, which in turn determines histocompatibility.