A substance-usually a protein-that the body recognizes as a foreign invader,triggering an immune response is an

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An antigen is a substance that triggers an immune response in the body, usually a protein or a carbohydrate. Antibodies are proteins produced by the immune system in response to the presence of antigens. Antihistamines are drugs that block the effects of histamine, which is released during an allergic reaction. Antibiotics are drugs used to treat bacterial infections.

A Substance-Usually a Protein-That the Body Recognizes as a Foreign