Your skin, mucous membranes, and stomach acid act as the castle walls.
An antigen is any substance that can be recognized by the immune system, including pathogens, parts of pathogens, or even substances not associated with pathogens. An epitope is a small part of an antigen that is recognized by the immune system. immunology made ridiculously simple pdf reddit link
Just let me know what topic you are stuck on! Share public link Your skin, mucous membranes, and stomach acid act