Step 1: Concept Overview:
Atopic allergy, or type I hypersensitivity, is an allergic reaction caused by a specific antibody class (immunoglobulin). The task is to identify this immunoglobulin.
Step 2: Detailed Explanation:
- IgE: This immunoglobulin triggers allergic reactions. Allergic individuals produce IgE antibodies against allergens (e.g., pollen). These IgE antibodies bind to mast cells and basophils. Subsequent exposure to the same allergen causes cross-linking of IgE on these cells, leading to degranulation and release of inflammatory mediators like histamine, resulting in allergic symptoms.
- IgG: The most prevalent immunoglobulin in blood, IgG is important for fighting bacterial and viral infections.
- IgM: The first antibody produced during an initial immune response. It exists as a pentamer and effectively activates the complement system.
- IgA: The primary immunoglobulin in mucosal secretions (saliva, tears, breast milk), providing initial defense at mucosal surfaces.
Step 3: Final Answer:
IgE is the immunoglobulin responsible for atopic allergy. Therefore, option (C) is correct.