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IMMUNE CELLS

Mast
Cells

Sense. Signal. Shape Tissue Responses.

Mast cells are granule-rich immune cells positioned in tissues near blood vessels, nerves and epithelial barriers. They release mediators that influence vascular responses, recruit other cells and contribute to host defense. These same mechanisms can also drive allergic inflammation.

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What Are Mast Cells?

Mast cells are tissue-resident cells of the myeloid lineage. Their cytoplasm contains secretory granules rich in histamine and proteases. Local factors, including stem-cell factor acting through KIT, support their maturation and survival.

Many mast cells carry IgE bound to high-affinity FcεRI receptors. Allergen-mediated cross-linking can trigger activation, but mast cells also respond through other receptors. Their functions vary with tissue location and the signals they receive.

How Mast Cells Respond to an Allergen

IgE-dependent activation is one important pathway; other signals can also activate mast cells.

1. Bind IgE

1. Bind IgE

IgE antibodies bind FcεRI receptors on the mast-cell surface during sensitization.

2. Cross-link receptors

2. Cross-link receptors

A matching allergen can bridge receptor-bound IgE and initiate intracellular signaling.

3. Release mediators

3. Release mediators

Granules release stored mediators; cells also produce lipid mediators and cytokines.

4. Change local responses

4. Change local responses

Signals affect nearby vessels and tissues and help recruit additional immune cells.

Key Functions of Mast Cells

Specialized cellular functions contribute to coordinated immunity.

1. Sense local conditions

1. Sense local conditions

Receptors detect selected microbial, immune and tissue-derived signals.

2. Release mediators

2. Release mediators

Histamine, proteases, lipid mediators and cytokines influence local responses.

3. Recruit immune cells

3. Recruit immune cells

Chemokines and vascular effects help bring additional leukocytes to tissues.

4. Shape tissue responses

4. Shape tissue responses

Interactions with stromal and epithelial cells contribute to remodeling and regulation.

Key Takeaways

  • Mast cells mature and act mainly within tissues.
  • Granules store mediators for rapid release.
  • IgE-dependent activation is one of several pathways.
  • Tissue environments shape mast-cell properties.
  • Protective and harmful effects can use the same mechanisms.
  • Mast cells and basophils are distinct cell lineages.

Mast Cells and Aging

People of different generations walking in a mountain landscape

Aging changes tissue environments; its effects on mast cells are context-dependent.

  • Cell density and distribution can differ across tissues.
  • Local inflammatory and stromal signals may change.
  • Mediator release is influenced by activation pathways.
  • Human evidence varies by tissue and disease setting.
  • Age alone does not predict an individual’s mast-cell activity.

Selected sources and references

Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.