Immune hypersensitivity is responsible for all of the following except:

• A. Transplant rejection
• B. Asthma
• C. Autoimmune diseases
• D. Chronic immune complex diseases

Answer: (A)

Hypersensitivity reactions are immune responses that cause tissue injury and are categorized into four types based on the mechanism: Type I is IgE-mediated (asthma is a classic example), Type II involves antibodies that target cells or tissues (antibody-mediated cytotoxicity), Type III involves immune complex deposition (chronic immune complex diseases), and Type IV is T-cell–mediated delayed-type hypersensitivity (autoimmune processes often involve this pathway as well). Asthma fits Type I because it is driven by allergen-triggered IgE on mast cells. Autoimmune diseases can involve antibodies or autoreactive T cells, engaging Type II, III, or IV mechanisms. Chronic immune complex diseases exemplify Type III hypersensitivity, where immune complexes deposit in tissues and provoke inflammation. Transplant rejection, while immune-mediated, is an alloimmune response to donor antigens and isn’t typically classified strictly as one of the four hypersensitivity categories in many exam contexts; it can involve antibodies (Type II) or T cells (Type IV) against donor MHC antigens, but it is described more broadly as alloimmunity rather than a classical hypersensitivity reaction. Therefore, transplant rejection is the exception.