Hypersensitivität

Hypersensitivität refers to an exaggerated or inappropriate immune response to an antigen that is normally harmless. This reaction can cause damage to the body's tissues. Hypersensitivity reactions are broadly classified into four types, designated Type I, Type II, Type III, and Type IV, based on the underlying immunological mechanism.

Type I hypersensitivity, also known as immediate hypersensitivity or allergy, involves IgE antibodies. Upon initial exposure to an allergen, IgE is produced and binds to mast cells and basophils. Re-exposure triggers the release of histamine and other mediators, leading to rapid onset symptoms like hives, asthma, or anaphylaxis.

Type II hypersensitivity reactions involve IgG or IgM antibodies that target antigens on cell surfaces or in the extracellular matrix. This can lead to cell lysis through complement activation or antibody-dependent cell-mediated cytotoxicity. Examples include autoimmune hemolytic anemia and transfusion reactions.

Type III hypersensitivity arises from the formation of immune complexes, consisting of antigens and antibodies, which deposit in tissues. These complexes activate the complement system and recruit inflammatory cells, causing tissue damage. Conditions like serum sickness and lupus erythematosus are examples.

Type IV hypersensitivity, also known as delayed-type hypersensitivity, is cell-mediated and involves T lymphocytes. It typically develops over 24 to 72 hours after exposure to an antigen. Contact dermatitis and the tuberculin skin test are classic examples. Management of hypersensitivity reactions often involves avoiding the trigger, using medications to suppress the immune response, or desensitization therapy.