Autoimmunity involves abnormal reactions against which of the following?

• A. Pathogens
• B. The body's own tissues
• C. Allergic reactions
• D. Immunodeficiency

Answer: (B)

Autoimmunity happens when the immune system loses tolerance to the body's own tissues and starts attacking self antigens. This misdirected response causes inflammation and damage in various organs because the body's own cells become the targets, rather than foreign invaders. The other scenarios describe different immune problems: defending against pathogens is the normal job of the immune system, allergies are hypersensitivities to harmless environmental substances often mediated by IgE, and immunodeficiency means the immune system is underactive and can’t fight infections. So the abnormal reactions target the body's own tissues.