Hypersensitivity reactions are an exaggerated immune response to otherwise harmless substances and antigens. This can lead to tissue damage or clinical manifestations. The underlying immune mechanism is what distinguishes the four kinds of hypersensitivity reactions.
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 allergies or insect bite allergies.
Type II hypersensitivity
- Also called antibody-mediated Cytotoxic Reactions.
- This is caused by binding IgG and IgM antibodies on antigens surfaced cells or tissues. It can result in complement activation or phagocytosis or antibody-dependent cell 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 called immune complex-mediated reactions.
- The formation and deposition immune complexes (antigens and antibodies) in various tissues results in complement activation or inflammation.
- The location of immuno complex deposition will determine the clinical manifestations. These may include arthritis or glomerulonephritis.
- Systemic lupus is erythematosus and rheumatoid are just a few examples.
Type IV Hypersensitivity
- Also called delayed-type hypersensitivity reactions.
- The activation and release of Cytokines and T lymphocytes (CD4+ T cells) causes tissue inflammation.
- 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.
- Contact dermatitis and tuberculin skin reactions are some examples.
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.