Summary
Molecules, usually on pathogens, that trigger an immune response.
In depth
An epitope is the exact part recognised. Antigens can be proteins, polysaccharides or lipids on pathogens, toxins, pollen or transplanted cells. Haptens are small molecules that become antigenic when attached to carriers, as in penicillin allergy.
Antigens are recognised by shape, so slight changes (such as in viruses) can escape immunity. Self-antigens normally do not trigger responses.
Remember: each antigen can have several different epitopes.
Antigens are recognised as native molecules by B cells and antibodies, but as processed peptides on MHC by T cells. Haptens are small molecules that trigger responses only when attached to a carrier protein, as in penicillin allergy, where the drug binds to serum proteins. Superantigens activate many T cells at once.
Good immunogens are large, foreign, complex and degradable. Adjuvants (such as alum) boost responses by activating innate cells. Autoantigens are normal body components that trigger autoimmune disease, and allergens are harmless substances that trigger allergic responses.
Example: the ABO blood group antigens are carbohydrates, and the Rh antigen is a protein, both important in transfusion.
Frequently asked questions
What is Antigens?
Molecules, usually on pathogens, that trigger an immune response.
Which area of biology covers Antigens, and how advanced is it?
Antigens is one of the 52 topics in Immunology & Disease. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Complement System, Vaccines, Adaptive Immunity.
Can you give an example of Antigens?
The ABO antigens on red cells.
What should I learn before Antigens?
Antigens is a Beginner topic, so no earlier topic is required. Other Beginner topics in Immunology & Disease that pair well with it include Immune System, Viruses, Innate Immunity.
What topics are related to Antigens?
The closest topics to Antigens are Complement System, Vaccines, Adaptive Immunity, Immune System. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Antigens?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Antigens. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is Antigens different from Complement System?
Antigens: Molecules, usually on pathogens, that trigger an immune response. Complement System: A cascade of blood proteins that punches holes in microbes and enhances phagocytosis. Read both side by side and note what each one explains.
How should I study Antigens step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Complement System and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.