Final answer:
A hypersensitivity reaction that leads to an allergic response is termed anaphylaxis, which is a severe and potentially fatal condition resulting from a Type I hypersensitivity reaction.
Step-by-step explanation:
A hypersensitivity reaction that produces an allergic response is called anaphylaxis. Anaphylaxis, also known as anaphylactic shock, is a systemic and potentially life-threatening type I hypersensitivity reaction. This condition is characterized by symptoms such as swelling of the tongue and trachea, blockage of airways, a dangerous drop in blood pressure, and the development of shock. These symptoms can be severe and may lead to death within minutes if not promptly treated with epinephrine and other emergency interventions. It is differentiated from other hypersensitivity reactions, such as Type III hypersensitivities like serum sickness, because it is immediate and involves IgE antibodies that sensitize mast cells, leading to their degranulation upon exposure to an allergen.