**Core Concept**
Histamine is a **biogenic amine** involved in various physiological processes, including allergic reactions, immune responses, and gastric acid secretion. It is stored in and secreted by specific cells throughout the body. The primary sources of histamine are **mast cells**, **basophils**, and **enterochromaffin-like cells** in the stomach.

**Why the Correct Answer is Right**
The correct answer is related to the cell type responsible for histamine secretion. **Mast cells** are a type of immune system cell that play a crucial role in the inflammatory process, particularly in allergic reactions. They release histamine in response to **allergens**, which then acts on **H1 receptors** to cause vasodilation, smooth muscle contraction, and increased vascular permeability.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the primary source of histamine secretion.
**Option B:** This option is also incorrect as it is not the correct cell type associated with histamine release.
**Option C:** This option is incorrect as it is not related to the primary function of histamine secretion.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that **mast cells** are the primary source of histamine, and their degranulation leads to the release of histamine, causing allergic symptoms.

**Correct Answer:** D. Mast cells.