An antigen is whereas an antibody is a foreign substance such as a protein or a polysaccharide to which lymphocytes respond; a globular protein that reacts with an antigen to eliminate the antigen an immunoglobulin that is produced by lymph nodes in response to bacteria; a foreign protein that enters the body and causes an immune reaction a hapten molecule that is complex in shape; an enzyme produced by the thymus gland that neutralizes antigens only on a pathogen; only in a human body. none of the above