## **Core Concept**
Anaphylaxis is a severe, life-threatening allergic reaction that involves multiple systems in the body. It is primarily mediated by the release of histamine and other chemical mediators from mast cells and basophils. The key immunoglobulin involved in this process is **IgE**, which plays a crucial role in triggering the allergic response.

## **Why the Correct Answer is Right**
The correct answer, **IgE**, is involved in anaphylaxis because it binds to the surface of mast cells and basophils. When an allergen binds to the IgE antibodies on these cells, it causes the cells to degranulate and release histamine, leukotrienes, and other mediators. This release of mediators leads to the clinical manifestations of anaphylaxis, including vasodilation, increased vascular permeability, smooth muscle contraction, and mucus secretion.

## **Why Each Wrong Option is Incorrect**
- **Option A: IgA** - While IgA is an important immunoglobulin involved in mucosal immunity and can play a role in allergic reactions, it is not the primary immunoglobulin involved in anaphylaxis.
- **Option B: IgG** - IgG is the most abundant immunoglobulin in the blood and provides long-term immunity against infections. It is not directly involved in the immediate hypersensitivity reactions like anaphylaxis.
- **Option D: IgM** - IgM is the first immunoglobulin produced in response to an infection and is very effective in activating the complement system. However, it is not primarily involved in anaphylactic reactions.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that anaphylaxis is often associated with **IgE-mediated** reactions, which can be triggered by a variety of allergens, including foods (e.g., peanuts, tree nuts), medications (e.g., penicillin), and insect stings. Understanding the role of IgE in anaphylaxis is crucial for both diagnosis and treatment.

## **Correct Answer: C. IgE**