Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Canine atopic dermatitis is characterized as a genetically predisposed tendency to develop IgE antibodies to environmental allergens, leading to a characteristic inflammatory and pruritic skin disease.
Reason (R) : Abnormality in the ratio between T helper 1 (TH1) cells and T helper 2 (TH2) cells is one of the causes of atopic dermatitis in dogs
In light of the above statements, choose the correct 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:

Remember the Th2 pathway:
Th2 bias \(\rightarrow\) IL-4 & IL-13 release \(\rightarrow\) B-cell class switching \(\rightarrow\) High IgE production \(\rightarrow\) Atopic allergy.
This immunologic cascade links the Th1/Th2 imbalance directly to the clinical features of atopic dermatitis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Canine Atopic Dermatitis (CAD) is a common, genetically predisposed inflammatory skin disease.
Its pathogenesis involves a combination of skin barrier defects and an exaggerated immune response to common environmental allergens (such as pollen, mold, and dust mites).

Step 2: Detailed Explanation:
Let us evaluate the Assertion and the Reason.
Assertion (A) is correct. Canine atopic dermatitis is characterized by a genetically predisposed tendency to synthesize allergen-specific IgE antibodies.
These IgE antibodies bind to mast cells in the skin.
Upon subsequent exposure, allergen cross-linking of IgE triggers mast cell degranulation and the release of inflammatory mediators (such as histamine, leukotrienes, and cytokines).
This leads to intense pruritus (itching) and characteristic erythematous skin lesions, typically on the face, ears, paws, and ventrum.
Reason (R) is also correct. The underlying immunological defect in CAD is an imbalance in the T-helper cell response.
In healthy individuals, there is a balance between Th1 cells (which drive cell-mediated immunity) and Th2 cells (which drive humoral immunity).
In atopic dogs, there is a bias towards a Th2-skewed immune response, particularly during the acute phase of the disease.
Th2 cells secrete interleukins like IL-4, IL-5, and IL-13.
These cytokines stimulate B cells to undergo class-switch recombination to produce high levels of IgE antibodies instead of IgG.
Therefore, the abnormality in the Th1/Th2 ratio (Reason) directly causes the genetically predisposed development of allergen-specific IgE antibodies described in the Assertion.
Thus, both (A) and (R) are true, and (R) is the correct explanation of (A).

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