12. What is an antigen?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
Antigen is any substance, or
infectious agent recognized foreign to
the body. contact of the antigen
the body promotes a
reaction against the antigen (,
specific or both).