MEDizzy - After receiving incompatible blood, a patient develops a

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General Pathology (II)

After receiving incompatible blood, a patient develops a transfusion reaction in the form of back pain, fever, shortness of breath, and hematuria. Which one of the following statements best classifies this type of immunologic reaction?

ExplanationA blood transfusion reaction is a type II hypersensitivity reaction that is mediated by antibodies reacting against antigens present on the surface of blood group antigens or irregular antigens present on the donor’s red blood cells. Type II hypersensitivity reactions result from attachment of antibodies to changed cell surface antigens or to normal cell surface antigens. Complement-mediated cytotoxicity occurs when IgM or IgG binds to a cell surface antigen with complement activation and consequent cell membrane damage or lysis. Blood transfusion reactions and autoimmune hemolytic anemia are examples of this form. Systemic anaphylaxis is a type I hypersensitivity reaction in which mast cells or basophils that are bound to IgE antibodies are reexposed to an allergen, which leads to a release of vasoactive amines that causes edema and broncho- and vasoconstriction. Sudden death can occur. Systemic immune complex reactions are found in type III reactions and are due to circulating antibodies that form complexes upon reexposure to an antigen (such as foreign serum), which then activates complement. This process is followed by chemotaxis and aggregation of neutrophils, which leads to release of lysosomal enzymes and eventual necrosis of tissue and cells. Serum sickness and Arthus reactions are examples of type III reactions. Delayed type hypersensitivity is type IV and is due to previously sensitized T lymphocytes, which release lymphokines upon reexposure to the antigen. This takes time—perhaps up to several days following exposure. The tuberculin reaction is the best-known example.