Type 2 hypersensitivity reactions are a group of immune-mediated responses that occur when the immune system mistakenly identifies normal host cells or tissues as foreign and attacks them. This reaction is mediated by antibodies, usually IgG or IgM, that bind to antigens on the surface of target cells or tissues, leading to destruction or dysfunction of those cells.
The antigens that trigger type 2 hypersensitivity reactions can be intrinsic or extrinsic. Intrinsic antigens are self-antigens that are expressed on the surface of normal cells, but the immune system recognizes them as foreign because they are structurally altered, as in autoimmune disorders. Extrinsic antigens are foreign antigens that are present on the surface of host cells, as in the case of drug-induced immune reactions.
Examples of type 2 hypersensitivity reactions include autoimmune hemolytic anemia, in which antibodies bind to and destroy red blood cells, and Goodpasture's syndrome, in which antibodies attack the basement membrane of the kidney and lungs. Other examples include transfusion reactions, where the immune system attacks donor blood cells, and drug-induced reactions, where the immune system attacks host cells that have been modified by drugs.
Type 2 hypersensitivity reactions can cause a range of symptoms, depending on the type and severity of the reaction. These can include anemia, hemolysis, organ damage, and in severe cases, anaphylaxis or shock. Treatment may involve avoiding the triggering antigen, suppressing the immune response with drugs, or replacing damaged or destroyed cells or tissues.
Summary Table
Type Type 1 Type 2 Type 3 Type 4 Reactant IgE IgG IgG T effector cells Mechanism Mast-cell activation releases histamines and other mediators Antigens embedded in host cells cause complement activation and destruction by MAC. Antibody binds to soluble antigen, forming a circulating immune complex lodges in a vessel wall and causes a local inflammatory response. APC activates Th1/CTL. T cells activation macrophages and cause an inflammatory response. Time course Minutes Days Example Anaphylaxis Acute Transfusion Reaction Rheumatoid Arthritis, Vasculitis, Glomerulonephritis Contact Dermatitis, Mantoux tuberculin test