**Core Concept:** IgE (Immunoglobulin E) receptors are part of the immune system, specifically involved in allergic reactions. They are found on the surface of certain immune cells, particularly mast cells and basophils.

**Why the Correct Answer is Right:** IgE receptors are indeed part of the Fc (Fragment Crystallizable) region of the immunoglobulin E molecule. When an allergen (substance that triggers an allergic response) binds to these IgE receptors, a series of events are initiated leading to the release of preformed mediators (histamine, heparin, serotonin, and prostaglandins) and de novo synthesized mediators (cytokines, chemokines, and leukotrienes). These mediators contribute to the allergic response, causing symptoms such as inflammation, bronchoconstriction, and vasodilation.

**Why Each Wrong Option is Incorrect:**

A. Mast cells are not the only cells involved in the allergic response. Basophils also play a significant role, and IgE receptors are present on their surface as well.

B. Although mast cells and basophils do express IgE receptors, the correct answer should include both cell types.

C. Selective IgE receptors on eosinophils are not the correct answer, as eosinophils are not directly involved in allergic reactions.

D. IgE receptors are present on both mast cells and basophils, which are crucial for the allergic response.

**Clinical Pearl:** Understanding the role of IgE receptors in allergic reactions is essential for clinical practice, as allergic reactions can have serious consequences and need proper management. Knowledge of the correct cell types involved (mast cells, basophils) is crucial for making an accurate diagnosis and choosing appropriate treatment strategies in patients with allergic conditions.