Final answer:
Allergens trigger an immune response by causing B cells to produce IgE antibodies, which bind to mast cells. Upon re-exposure to the same allergen, the mast cells release histamines, leading to allergic symptoms. Severe reactions, such as anaphylactic shock, need immediate epinephrine treatment.
Step-by-step explanation:
Allergic reactions are triggered when your immune system responds to a foreign substance, known as an allergen, that's typically harmless to most people. When someone is exposed to an allergen for the first time, their B cells produce IgE antibodies specifically for that allergen. These antibodies then attach to mast cells, which are found in connective tissues throughout the body. On subsequent exposure to the same allergen, the mast cells, already primed with IgE antibodies, quickly respond by releasing substances like histamines and cytokines, which cause the symptoms of an allergic reaction such as itching, swelling, and inflammation. This reaction can be mild or, in cases such as anaphylactic shock, life-threatening. Treatment of severe allergic reactions often requires the administration of epinephrine.