Epitopes are specific target structures recognized by the immune system of human or animal body. The human immune system can recognize a wide range of different epitopes. Antibodies are proteins that the immune system that react with its antigen target (which usually are proteins in invading organisms or foreign materials such as food proteins). If we think that the antibodies are keys that correspond to a lock target located in the antigen, the epitope would slot corresponding to a specific key. The epitope is generally a patch of amino acid residues, the building blocks of proteins. The epitope is located in the antigen where the antigen molecule docks, like a key that opens the lock.