Most often, antigens are composed of view available hint(s) most often, antigens are composed of polysaccharides lipids glycoproteins nucleic acids

Most often, antigens are composed of glycoproteins. An antigen is a molecule with the possibility to induce an immune response. An antigen is recognized inside the body by antibodies produced to match an antigen and to come into contact with it. Antigens can be peptides (amino acid chains), polysaccharides or lipids.

They are all in a iving organism.