IGCSE Biology glossary
Antigen
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A molecule (usually a protein) found on the surface of a cell or pathogen that the immune system can recognise as foreign. Each type of pathogen has unique antigens, which trigger a specific immune response involving antibody production by lymphocytes.
What to include in an exam answer
Antigens are ON the pathogen; antibodies are PRODUCED by lymphocytes. This is the most commonly confused pair. The antibody has a complementary shape to the antigen.
Example in context
Distinguish between an antigen and an antibody (2 marks): An antigen is a protein on the surface of a pathogen that triggers an immune response. An antibody is a protein produced by lymphocytes that has a complementary shape to a specific antigen and binds to it.
Related syllabus topic
Diseases & immunity