Which of the following is an example of Type I hypersensitivity?

• A. Lupus
• B. Bee sting
• C. Chronic graft rejection
• D. PPD reaction

Answer: (B)

Type I hypersensitivity, also known as immediate hypersensitivity, is an allergic reaction that occurs within minutes of exposure to an allergen. This type of hypersensitivity is primarily mediated by IgE antibodies, which bind to allergens and trigger the release of histamine and other mediators from mast cells and basophils. This release leads to symptoms such as itching, swelling, and anaphylaxis in severe cases.

A bee sting is a classic example of Type I hypersensitivity. When a person who is allergic to bee venom gets stung, their immune system quickly reacts to the venom as if it were a harmful substance. The reaction can result in localized swelling and redness, or it may escalate to a more severe systemic response, including anaphylaxis. This immediate response is characteristic of Type I hypersensitivity.

In contrast, lupus is an autoimmune disease associated with Type III hypersensitivity, chronic graft rejection is a Type IV hypersensitivity reaction involving T-cell mediated immune responses, and a PPD reaction (purified protein derivative) is typically a measure of cell-mediated immunity and is associated with Type IV hypersensitivity as well. Understanding these distinctions is essential for recognizing the various types of hypersensitivity reactions.