Question

Which of the following is called as cell-mediated (delayed) hypersensitivity:

• A. Type II hypersensitivity
• B. Type I hypersensitivity
• C. Type III hypersensitivity
• D. Type IV hypersensitivity

Answer 1

The Correct Option is D

The correct option is (D): Type IV hypersensitivity.

Answer 2

The question asks which type of hypersensitivity reaction is described as cell-mediated and delayed. Let's look at what drives each type.

1. Type II hypersensitivity: This reaction is driven by antibodies that bind directly to antigens on the surface of the body's own cells, causing cell destruction, as seen in hemolytic anemia. It is antibody-driven, not cell-mediated.
2. Type I hypersensitivity: This is the classic immediate allergic reaction, driven by IgE antibodies that trigger mast cells to release histamine within minutes of exposure, as in anaphylaxis. Its speed makes it the opposite of a delayed reaction.
3. Type III hypersensitivity: This type happens when antigen-antibody complexes form and deposit in tissues such as blood vessels or joints, triggering inflammation, as in serum sickness. It is also antibody-based and develops over hours to days, but it is not classified as cell-mediated.
4. Type IV hypersensitivity: Unlike the other three, this reaction does not involve antibodies at all. It is driven by sensitized T lymphocytes and macrophages, and takes 24 to 72 hours to fully develop, as seen in contact dermatitis and the tuberculin skin test. This slow, T-cell driven pattern is exactly what "cell-mediated (delayed)" describes.

Only type IV hypersensitivity is both driven by cells rather than antibodies and slow to develop, matching the description in the question.

Therefore, the correct answer is Type IV hypersensitivity.