Mast cells and basophils are the primary cells that release histamine.
Histamine is a crucial mediator involved in various physiological and pathological processes, most notably in allergic reactions and inflammation. Understanding which cells release histamine helps clarify these processes.
Key Histamine-Releasing Cells
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Mast Cells: These are tissue-resident immune cells found throughout the body, particularly in areas exposed to the external environment like the skin, lungs, and gastrointestinal tract. Mast cells store histamine in cytoplasmic granules and release it upon activation by various stimuli, including allergens, IgE antibodies, complement components, and certain neuropeptides.
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Basophils: Basophils are a type of white blood cell circulating in the bloodstream. Similar to mast cells, they contain histamine-filled granules and release histamine when activated, often in response to allergens and IgE.
Storage and Release of Histamine
Histamine is stored within granules in both mast cells and basophils, alongside other substances like:
- Serotonin
- Proteases
- Proteoglycans
- Cytokines and chemokines
- Angiogenic factors
Upon activation, these cells undergo a process called degranulation, where the granules fuse with the cell membrane and release their contents, including histamine, into the surrounding environment.
Factors that Trigger Histamine Release
Several factors can trigger histamine release from mast cells and basophils:
- Allergens: Binding of allergens to IgE antibodies on the cell surface triggers degranulation.
- Complement Components: Certain complement proteins (e.g., C3a, C5a) can activate mast cells and basophils.
- Neuropeptides: Some neuropeptides, like substance P, can induce histamine release.
- Physical Stimuli: Physical stimuli like heat, cold, or mechanical trauma can also trigger histamine release in certain scenarios.
Role of Histamine
Once released, histamine binds to histamine receptors (H1, H2, H3, and H4) on various cells, leading to diverse effects, including:
- Vasodilation
- Increased vascular permeability
- Bronchoconstriction
- Increased mucus production
- Itching
- Acid secretion in the stomach
These effects contribute to the symptoms observed in allergic reactions and inflammatory conditions.
