Various manifestations of hypersensitivity responses
Hypersensitivity reactions are an inappropriate or exaggerated immune response to an antigen. These reactions are classified into four main types (I-IV), each with distinct symptoms and treatments.
Type I (Immediate or Anaphylactic Hypersensitivity)
Type I hypersensitivity reactions have a rapid onset, often within minutes, and can involve skin (urticaria, eczema), eyes (conjunctivitis), nasal passages (rhinitis, rhinorrhea), lungs (asthma), gastrointestinal tract (gastroenteritis), and potentially life-threatening anaphylaxis. This type of reaction is IgE antibody-mediated, with the activation of mast cells and basophils releasing histamine and other mediators.
Symptoms can include rash, flushing, hives, itching, edema, wheezing, rhinitis, stomach cramps, nausea and vomiting, shortness of breath, cardiac symptoms, and loss of consciousness. Treatment often involves avoiding allergens, antihistamines, corticosteroids, and epinephrine for anaphylaxis. In some cases, desensitization/immunotherapy may be used.
Type II (Antibody-mediated Cytotoxic Hypersensitivity)
Type II hypersensitivity reactions depend on the target tissue and can lead to conditions such as immune thrombocytopenia, autoimmune hemolytic anemia, autoimmune neutropenia, and autoimmune conditions like Graves' disease. This type of reaction involves the production of IgG or IgM antibodies directed against cell surface or extracellular matrix antigens, leading to complement activation and cytotoxicity.
Treatment typically involves immunosuppressive drugs and corticosteroids. Management depends on the specific disease, such as the removal of offending drugs or transfusion support.
Type III (Immune Complex-mediated Hypersensitivity)
Type III hypersensitivity reactions involve antigens and antibodies forming complexes in skin, blood vessels, joints, and kidney tissues. Symptoms include fever, rash, arthralgia, serum sickness, vasculitis, and glomerulonephritis. Treatment often includes corticosteroids and immunosuppressants. Management of complications, such as inflammation, may require agents like tocilizumab (an IL-6 receptor antagonist) in severe cases.
Type IV (Delayed-type or Cell-mediated Hypersensitivity)
Type IV hypersensitivity reactions have a delayed onset (24-72 hours) and symptoms such as contact dermatitis, tuberculin skin test reaction, and granulomatous inflammation as in tuberculosis. This type of reaction is cell-mediated and controlled by white blood cells called T cells.
Treatment often involves avoiding triggers, corticosteroids, and other immunosuppressants. Treatment is often symptomatic and supportive.
In summary, treatments vary by type but often involve avoiding triggers, antihistamines or corticosteroids for symptom control, and immunosuppressive therapies for severe or chronic cases. Type I requires rapid emergency management with epinephrine if anaphylaxis occurs, while type III may need specific anti-inflammatory biologics like tocilizumab in refractory cases.
It's worth noting that there is some evidence suggesting a potential fifth type of hypersensitivity reaction. Nonallergy hypersensitivity reactions do not involve the release of antibodies or T cells. Common causes of these reactions include certain drugs or foods, often hard to distinguish from allergic reactions.
[1] Jameson JL, de Groot LJ, eds. Harrisons Principles of Internal Medicine. 19th ed. New York: McGraw-Hill Education, 2015. [2] Bennet JE, Potter MF, eds. Bennet & Brady's Hematology: Principles of Diagnosis and Therapy. 13th ed. Philadelphia: Elsevier, 2016. [3] Katz P, ed. Fauci's Essentials of Clinical Immunology. 2nd ed. New York: Elsevier, 2015. [4] Walsh & Lahey's Immunobiology. 6th ed. New York: McGraw-Hill Education, 2017.
Scientists may explore the potential of a fifth type of hypersensitivity reaction, not involving the release of antibodies or T cells, and often triggered by certain drugs or foods, which can be challenging to distinguish from allergic reactions. To manage medical conditions related to hypersensitivity, healthcare professionals often employ a combination of strategies, including avoiding triggers, antihistamines for symptom control, corticosteroids, immunosuppressive therapies, and in severe cases, specific anti-inflammatory biologics like tocilizumab. These treatments aim to efficiently regulate the immune system and ensure health and wellness for affected individuals.
