Hypersensitivity reaction refers to an exaggerated or excessive immune response triggered by the exposure to certain substances, known as allergens. It is a condition in which the immune system overreacts and produces a heightened response against normally harmless substances like pollen, dust mites, certain foods, medications, or insect bites, resulting in various symptoms and signs.
These reactions are classified into four types, namely type I, type II, type III, and type IV hypersensitivity reactions, based on the specific immune mechanisms involved. Type I hypersensitivity, also known as immediate hypersensitivity, involves activation of antibodies called IgE, resulting in a rapid release of chemicals such as histamine and leukotrienes from mast cells and basophils. This is responsible for the characteristic symptoms observed in conditions like allergic rhinitis, asthma, and anaphylaxis.
Type II hypersensitivity occurs when the immune system produces antibodies against specific target cells or tissues, leading to their destruction or dysfunction. Examples include autoimmune diseases like rheumatoid arthritis and hemolytic anemia.
Type III hypersensitivity involves the formation of immune complexes between antigens and antibodies, which can then deposit in various tissues, causing inflammation. Conditions like systemic lupus erythematosus and vasculitis are associated with type III hypersensitivity reactions.
Type IV hypersensitivity, also called delayed hypersensitivity, involves activation of specific T-lymphocytes, resulting in inflammation and tissue damage. This type of reaction is observed in conditions like contact dermatitis and certain drug allergies.
Overall, hypersensitivity reactions can manifest in various ways, including skin rashes, itching, swelling, respiratory symptoms, gastrointestinal disturbances, and even life-threatening symptoms in severe cases. Proper evaluation and management by healthcare professionals are essential to alleviate symptoms and prevent complications in individuals with hypers
