Discuss about how hipper sensitivity reactions occurs
Hypersensitivity reactions, also known as allergic reactions, occur when the immune system overreacts to a harmless substance, such as pollen, certain foods, medications, or insect stings. These reactions can range from mild to severe and can affect various parts of the body.
Hypersensitivity reactions are classified into four types based on the immune mechanisms involved in the reaction:
1. Type I hypersensitivity (immediate hypersensitivity):
In type I hypersensitivity, the body produces large amounts of immunoglobulin E (IgE) antibodies in response to the allergen. These antibodies attach to mast cells and basophils, which are cells involved in the immune response. Upon re-exposure to the allergen, it binds to the IgE antibodies, triggering the release of various chemicals, including histamine, prostaglandins, and leukotrienes. These chemicals cause symptoms such as itching, hives, nasal congestion, wheezing, and in severe cases, anaphylaxis.
2. Type II hypersensitivity (cytotoxic hypersensitivity):
Type II hypersensitivity occurs when antibodies, typically Immunoglobulin G (IgG) or Immunoglobulin M (IgM), bind to antigens on the surface of cells, leading to their destruction. This can happen in autoimmune diseases or as a result of medications or transfusions. Examples include hemolytic reactions in blood transfusions or drug-induced immune thrombocytopenia.
3. Type III hypersensitivity (immune complex-mediated hypersensitivity):
In type III hypersensitivity, immune complexes of antigens and antibodies are formed and deposited in tissues, triggering inflammation and tissue damage. These complexes can activate complement proteins, attract inflammatory cells, and cause localized or systemic damage. Examples include systemic lupus erythematosus and immune complex-mediated vasculitis.
4. Type IV hypersensitivity (delayed-type hypersensitivity):
Type IV hypersensitivity reactions involve T-cell mediated responses and do not require antibody production. Sensitized T-cells, upon re-exposure to the allergen or antigen, release cytokines that recruit inflammatory cells, leading to tissue damage. This type of hypersensitivity is associated with allergic contact dermatitis, such as poison ivy reactions, and some autoimmune diseases like multiple sclerosis.
It's important to note that the severity and symptoms of hypersensitivity reactions can vary greatly. Mild reactions may result in symptoms like itching or a rash, while severe reactions can lead to anaphylaxis, a life-threatening condition that involves respiratory distress, a drop in blood pressure, and organ failure. Management of hypersensitivity reactions involves allergen avoidance, medications like antihistamines or corticosteroids, and in severe cases, emergency medical intervention.