**Core Concept:** Type I hypersensitivity is a part of the immediate hypersensitivity response, which is initiated by the activation of mast cells and basophils by immunoglobulins. It is characterized by histamine release, causing the typical signs and symptoms of allergy.

**Why the Correct Answer is Right:** In Type I hypersensitivity, immunoglobulin E (IgE) is the key molecule involved. It binds to high-affinity IgE receptors (FcεRI) on the surface of mast cells and basophils. Upon exposure to the allergen, cross-linking of these IgE-FcεRI complexes leads to degranulation, releasing histamine and other mediators that cause the clinical manifestations of allergy (e.g., vasodilation, increased vascular permeability, bronchoconstriction, and inflammation).

**Why Each Wrong Option is Incorrect:**

A. IgA (Immunoglobulin A) is not involved in Type I hypersensitivity. IgA is primarily involved in mucosal immunity and defense against pathogens in the gut and respiratory tract.

B. IgD (Immunoglobulin D) is not associated with immediate hypersensitivity reactions. It plays a role in B cell activation and immune surveillance.

C. IgE (Immunoglobulin E) is the correct answer, as mentioned above.

D. IgG (Immunoglobulin G) is not involved in Type I hypersensitivity reactions. It plays a role in complement activation, immune complex-mediated reactions, and neutralization of toxins and viruses.

**Clinical Pearl:** Understanding the role of immunoglobulins in allergic reactions is crucial for diagnosing and managing patients with allergic diseases. It helps in differentiating between immediate and delayed hypersensitivity reactions and choosing the appropriate treatment strategies.