This program explores the wide range of defense mechanisms the body calls upon to fight foreign invaders in an effort to maintain health. Immune responses, diseases, and care of the immune system are some of the topics addressed. Concepts and terminology include: pathogen, defenses, lymph, phagocytes, macrophages, lymphocytes, humoral immunity, antibody, acquired immunity, vaccines, allergies, autoimmune disorders, AIDS, immune disorders, and care of the immune system. .