Type I hypersensitivity, also known as immediate hypersensitivity or allergy, is a form of hypersensitivity reaction triggered by exaggerated immune responses to certain substances, known as allergens. This particular type of hypersensitivity is marked by the release of large amounts of immunoglobulin E (IgE) antibodies in response to the presence of allergens.
Upon initial exposure to an allergen, these IgE antibodies are produced and bind to the surface of specialized immune cells, known as mast cells and basophils. On subsequent re-exposure to the same allergen, the allergen binds to the IgE antibodies already present on these cells, causing the release of various chemicals, such as histamine, leukotrienes, and prostaglandins.
The release of these chemical mediators results in the symptoms characteristic of type I hypersensitivity, which can manifest in various forms depending on the site these chemicals affect. Common examples of type I hypersensitivity reactions include allergic rhinitis (hay fever), asthma, atopic dermatitis (eczema), and food allergies.
Clinical manifestations of type I hypersensitivities can range from mild symptoms like sneezing, itching, and localized skin reactions, to more severe and potentially life-threatening anaphylactic reactions, including difficulty breathing, swelling, and a drop in blood pressure.
Treatment options for type I hypersensitivities often involve avoidance of the allergen, administration of antihistamines to block the effects of histamine, and in severe cases, the use of epinephrine (adrenaline).
