Allergic (hypersensitive) is caused by immune response to several antigen. Antigen which can induce allergic response in known as allergen.
Immediate type Hypersensitivity Reaction
Immediate-type hypersensitivity reaction, such as bee sting, allergic to pollen or pet, is caused by humoral immunity mechanism. The immunity is mediated by antibody secretion into body fluid to fight invader antigen. Immediate-type hypersensitivity reaction is generated by antibody igE production. When someone has allergen, the antibody IgE will bind with white blood cells containing histamine, which is a chemical substance causing general allergic symptom, such as wet nose, watery eyes, and sneezing. If the binding site between antigen and white blood cell is filled with allergen, the white blood cell will release histamine.
Delayed-Type Hypersensitivy Reaction
Slow allergic reaction is known as delayed-type hypersensitivity or DTH, i.e the poisonous case by poison-ivy or poisonous oak tree. The example of extreme DTH occurs when macrophage has difficulty in destroying the invander. Consequently, T cell is activated and causing tissue inflammation. This condition continuously occurs as long as T cell is activated.