What are the common diseases associated with each type of allergic reaction?

Allergy, also known as hypersensitivity, refers to abnormal and excessive immune responses. There are four main types, each associated with different common diseases. 1. IgE-mediated (Type I): Common diseases include urticaria, asthma, and allergic rhinitis. This type of reaction is triggered when IgE antibodies bind to the corresponding antigens, causing cells to release biologically active mediators, leading to symptoms such as smooth muscle contraction and increased glandular secretion. 2. Antibody-mediated cytotoxic (Type II): This type mainly involves damage to red blood cells, granulocytes, or platelets. Common diseases include autoimmune hemolytic anemia, hemolytic disease of the newborn, neutropenia, and thrombocytopenic purpura. 3. Immune complex-mediated (Type III): The main pathological features are edema, cellular infiltration, and hemorrhagic necrosis. Common diseases include acute glomerulonephritis, systemic lupus erythematosus, and rheumatoid arthritis. 4. Cell-mediated or delayed-type (Type IV): Common diseases include contact dermatitis and eczema. This type of reaction is unrelated to antibodies; it occurs when sensitized lymphocytes bind to corresponding antigens and release lymphokines, resulting in a delayed response that typically appears 12 to 24 hours after re-exposure to the antigen.