Hypersensitivity reactions are an exaggerated immune response to otherwise harmless substances and antigens. This can lead to tissue damage or clinical manifestations. You can find four different types of hypersensitivity reactions. They are classified according to their underlying immune mechanisms.
Type I Hypersensitivity
- Also called immediate hypersensitivity, allergic reactions.
- The release of histamines and other mediators by mast cells and basophils is triggered when immunoglobulin E antibodies (IgE), are used.
- There are many clinical signs that can be seen in patients, including angioedema.
- You can have allergic rhinitis or food allergy, drug allergy, insect sting allergy, or both.
Type II hypersensitivity
- Also known as antibodymediated cytotoxic reaction.
- The binding of IgG/IgM antibodies onto antigens on cells and tissues results in complement activation, cell death, or antibody dependent cellular cytotoxicity.
- The clinical manifestations of hemolytic anemia depend on the tissue target and can include thrombocytopenia and autoimmune disorders as well as drug-induced immune responses.
- These include drug-induced hemocytopenia, Rh disease and autoimmune hemolyticanemia.
Type III Hypersensitivity
- Also known as immune complex mediated reactions.
- The formation and deposition immune complexes (antigens and antibodies) in various tissues results in complement activation or inflammation.
- Clinical manifestations are dependent on where the immune complex is deposed and can include vasculitis and arthritis.
- Serum sickness, systemic lupus-erythematosus, and rheumatoid arthritis are some examples.
Type IV Hypersensitivity
- Also called delayed-type hypersensitivity reactions.
- This is caused by activation of CD4+ T lymphocytes and release of cytokines.
- Most commonly, clinical manifestations are seen within 24 to 48 hours following exposure to the antigen. These may include contact Dermatitis, tuberculin test reactions, and graft failure.
- These include: contact dermatitis; tuberculin-related skin reaction reactions; and rejection of grafts.
Hypersensitivity reactions can be managed depending on their severity. You can avoid the trigger agent and use pharmacologic treatment (e.g. corticosteroids or antihistamines) to reduce your symptoms. In some cases, you may also need desensitization. The use of immunomodulatory treatments and allergen specific immunotherapy can help prevent hypersensitivity reactions.