A patient is seen in the emergency department after a bee sting caused bronchospasm and severe pruritis. The nurse understands that this type of hypersensitivity reaction is known as
• The patient is suffering from a type I reaction (anaphylaxis) due to IgE-mediated histamine release.
• A type I (anaphylactic): an immediate allergic reaction involving IgE. The reaction may involve skin (urticaria or itching), eyes (conjunctivitis), nasopharynx (rhinorrhea, rhinitis), dyspnea, and cramping or diarrhea. Examples include anaphylaxis, angioedema, allergic conjunctivitis, and hay fever.
• A type II (cytotoxic): a process involving IgG and IgM as they bind to antigens, activating the complement pathway. Though primarily mediated by antibodies of the IgM or IgG classes and complement, phagocytes and K cells may also play a role. This leads to cell lysis. Examples include ABO incompatibility, drug-induced hemolytic anemia, Goodpasture's nephritis, granulocytopenia, and thrombocytopenia. Treatment involves anti-inflammatory and immunosuppressive agents.
• A type III (immune complex): involves antigen-antibody complexes that are not adequately cleared, leading to an inflammatory response. The reaction may take 3–10 hours after exposure to the antigen. It is mediated by soluble immune complexes and complement (C3a, and 5a). They are mostly of the IgG class, although IgM may also be involved. The damage is caused by platelets and neutrophils. Neutrophils and deposits of immune complexes and complement are seen. Examples include lupus, aspergillosis, polyarteritis, and post-streptococcal glomerulonephritis.
• A type IV (cell-mediated): also called a delayed hypersensitivity reaction, involves sensitized T-cells and takes several days to develop. The classical example of this hypersensitivity is tuberculin () reaction, which peaks 48 hours after the injection of antigen (PPD or old tuberculin). The lesion is characterized by induration and erythema. Type IV hypersensitivity is involved in the pathogenesis of many autoimmune and infectious diseases (tuberculosis, leprosy, histoplasmosis, toxoplasmosis) and granulomas, due to infections and foreign antigens. Another example is contact dermatitis (poison ivy).