This program examines how the human immune system defends the body against disease-causing invaders—and how in some cases its antigen-fighting capabilities can be turned against the bodily cells it protects. Topics include the elements of the immune system, passive barrier defenses and nonspecific reactive responses, the humoral immune response and its associated antibodies, and the process of cell-mediated immunity. The program also addresses the importance of vaccines, the mechanics of allergies and autoimmune diseases, and advances in the field of immunology. A viewable/printable instructor’s guide is available online. A Films for the Humanities & Sciences Production. A part of the series The Human Body: How It Works. (22 minutes)