Multiple choice

Which of the following is true for allergic reactions?

  1. Arthus reaction is a type IV reaction.

  2. Anaphylaxis occurs in patients who have had no previous exposure to the offending substance.

  3. Contact dermatitis is a type IV reaction.

  4. Positive Mantoux test is a type III reaction.
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C Correct answer
Explanation

Contact dermatitis (e.g., poison ivy reaction, nickel allergy) is a classic Type IV hypersensitivity reaction, which is T-cell mediated and delayed (48-72 hours). The Arthus reaction is Type III (immune complex mediated), anaphylaxis requires previous sensitization (Type I), and the Mantoux test is also Type IV (delayed-type hypersensitivity).

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