Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Allergy to penicillin is example of Type 1 hypersensitivity and may be sometimes with fatal outcome.
Reason (R) : Type 1 hypersensitivity is mediated by IgE and Mast cell which undergo degranulation leading to heavy release of histamine that cause vasodialation
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true and (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

To confirm an Assertion-Reason relationship, read them together using "because":
"Allergy to penicillin is a Type I hypersensitivity that can be fatal because it is mediated by IgE and Mast cells releasing histamine, which causes massive vasodilation."
This makes sense, so (R) is the correct explanation of (A).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Hypersensitivity reactions are exaggerated or inappropriate immune responses that cause tissue damage.
According to the Gell and Coombs classification, hypersensitivity is divided into four types (Types I, II, III, and IV).
Type I (immediate) hypersensitivity is mediated by IgE antibodies and involves rapid mast cell degranulation.

Step 2: Detailed Explanation:
Let us evaluate the Assertion and the Reason.
Assertion (A) is correct. An allergy to penicillin is a classic example of Type I (immediate) hypersensitivity.
In sensitized animals, subsequent exposure to penicillin (which acts as a hapten binding to tissue proteins) can trigger a rapid, systemic allergic response known as anaphylaxis.
This can cause severe bronchoconstriction, systemic vasodilation, and cardiovascular collapse, potentially leading to a fatal outcome if not treated promptly.
Reason (R) is also correct. The underlying mechanism of Type I hypersensitivity involves the production of allergen-specific IgE antibodies upon first exposure.
These IgE antibodies bind to high-affinity Fc\(\epsilon\)RI receptors on the surface of tissue mast cells and blood basophils.
Upon re-exposure, the allergen cross-links the membrane-bound IgE, triggering intracellular signaling pathways that lead to degranulation.
This degranulation releases preformed vasoactive amines, primarily histamine, into the tissues.
Histamine acts on H1 and H2 receptors, causing smooth muscle contraction (bronchospasm) and widespread vasodilation.
This vasodilation, along with increased capillary permeability, leads to a rapid drop in blood pressure and circulatory shock.
Since the mechanism described in the Reason directly explains why penicillin allergy can cause a rapid, potentially fatal anaphylactic reaction, both (A) and (R) are true, and (R) is the correct explanation of (A).

Step 3: Final Answer:
The correct option is (A).