Mast cells secrete a protein, which causes the dilation of blood vessels. The protein is

Options

A. Pyrogens
B. Histamine
C. Interferon
D. None of these

Answer

**Step-by-Step Solution:**

1. **Identify the Source of the Protein**: The question states that mast cells secrete a protein that causes the dilation of blood vessels.

2. **Understand the Function of Mast Cells**: Mast cells are a type of immune cell that play a crucial role in the body's defense mechanisms. They are involved in allergic reactions and inflammation.

3. **Identify the Protein Secreted by Mast Cells**: The protein that is primarily secreted by mast cells is histamine. Histamine is known for its role in allergic responses and is a key mediator in the dilation of blood vessels.

4. **Explain the Role of Histamine**: When histamine is released, it causes blood vessels to dilate (widen), which increases blood flow to the affected area. This dilation is responsible for the redness and swelling often seen during inflammatory responses.

5. **Evaluate Other Options**:
- **Pyrogens**: These are substances that induce fever and increase body temperature, not involved in blood vessel dilation.
- **Body Temperature**: This is not a protein and does not relate to the question.
- **Interferon**: This is a protein that helps to protect cells from viral infections and has no role in blood vessel dilation.

6. **Conclude with the Correct Answer**: Based on the information, the correct answer to the question is histamine, which is secreted by mast cells and causes the dilation of blood vessels.

**Final Answer**: The protein secreted by mast cells that causes the dilation of blood vessels is **histamine**.

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