Histamine is released from mast cells during an allergic immune response.

Mast cells and their Role in Allergic Immune Response:
Mast cells are a type of white blood cell found in tissues throughout the body, particularly in areas that are exposed to the external environment, such as the skin, respiratory tract, and gastrointestinal tract. They play a crucial role in the immune response, especially in allergic reactions.

The Release of Histamine:
Histamine is a chemical compound that is released during an allergic immune response and is responsible for many of the symptoms associated with allergies, such as itching, redness, and swelling. Histamine is stored in specialized granules within mast cells, known as mast cell granules.

When an allergic trigger, such as pollen or pet dander, comes into contact with the body, it binds to specific receptors on the surface of mast cells. This binding triggers a signaling cascade within the mast cell, leading to the release of histamine from the granules.

Function of Histamine in Allergic Response:
Histamine has several effects on the body during an allergic immune response. Some of the key effects include:

1. Vasodilation: Histamine causes the blood vessels to widen, leading to increased blood flow to the affected area. This results in redness and warmth.

2. Increased Vascular Permeability: Histamine increases the permeability of blood vessels, allowing fluid and immune cells to move more easily from the blood into the surrounding tissues. This leads to swelling and edema.

3. Smooth Muscle Contraction: Histamine can cause the smooth muscles lining the airways to contract, leading to bronchoconstriction and difficulty breathing. It can also cause smooth muscle contraction in the gastrointestinal tract, leading to abdominal cramps and diarrhea.

4. Itching and Pain: Histamine can stimulate nerve endings, leading to sensations of itching and pain.

In summary, histamine is released from mast cells during an allergic immune response. It plays a central role in the development of allergic symptoms by causing vasodilation, increased vascular permeability, smooth muscle contraction, and itching. Understanding the role of histamine and mast cells helps in the development of therapies and medications for treating allergies.