Mediator present in mast cells is
**Core Concept**
Histamine is a key mediator stored in mast cells, released in response to allergic reactions, inflammation, and anaphylaxis. It plays a crucial role in modulating the immune response and mediating symptoms such as vasodilation, increased vascular permeability, and smooth muscle contraction.
**Why the Correct Answer is Right**
Histamine is stored in mast cells in the form of histamine-containing granules, which are released when mast cells are activated by IgE antibodies, complement system components, or other stimuli. Upon release, histamine binds to H1 receptors on smooth muscle cells, endothelial cells, and other targets, leading to vasodilation, increased vascular permeability, and smooth muscle contraction. Histamine also stimulates the release of other mediators, such as leukotrienes and prostaglandins, which contribute to the inflammatory response.
**Why Each Wrong Option is Incorrect**
**Option A:** Tryptase is a serine protease enzyme stored in mast cells, released in response to allergic reactions, but it is not a mediator.
**Option B:** Cytokines are signaling molecules released by immune cells, including mast cells, but they are not stored in mast cell granules.
**Option C:** Leukotrienes are lipid mediators involved in inflammation, but they are produced from arachidonic acid by leukocytes, not stored in mast cells.
**Clinical Pearl / High-Yield Fact**
Mast cell degranulation and histamine release can lead to symptoms such as pruritus, urticaria, angioedema, and anaphylaxis. Antihistamines, such as diphenhydramine, can block H1 receptors to alleviate these symptoms.
**Correct Answer:** D. Histamine