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Immunology · Immune cells

Mast cell and basophil !

  • Cell

Mast cells in tissues and basophils in blood carry IgE on their surface and, when an allergen binds it, release histamine within minutes.

Updated 2026-11-01

What it is

Mast cells and basophils are related granulated cells that coat themselves with IgE through the high-affinity receptor FcεRI. When an allergen cross-links that IgE, they degranulate, releasing histamine and other mediators that open and leak blood vessels, tighten airways and cause itch. Mast cells live for a long time in tissues at the borders with the outside world; basophils are the rare circulating version.

Key facts

  • Origin: bone marrow; mast-cell progenitors finish maturing in tissue.
  • Basophils are the only circulating leukocytes that contain histamine and are an early source of IL-4.
  • Mast cells can also be triggered without IgE, by complement fragments (C3a, C5a) and some drugs.

Step by step

  1. First exposure: Th2 help leads B cells to make IgE against an allergen.
  2. IgE binds FcεRI on mast cells and basophils (sensitization).
  3. Next exposure: the allergen cross-links two IgE molecules on the surface.
  4. Granules release histamine and tryptase within minutes: wheal, itch, bronchospasm, low blood pressure.
  5. Hours later, newly made leukotrienes and cytokines recruit eosinophils for the late phase.

Markers

  • FcεRI
  • CD117 (KIT, mast cell)
  • Tryptase
  • CD123 (basophil)
  • Toluidine blue (metachromatic)

Clinical notes

  • Anaphylaxis: rapid, multi-system reaction (skin, airway, circulation, gut) to foods, medicines or insect stings; a medical emergency.
  • Allergic rhinitis, urticaria and allergic asthma are mast-cell driven.
  • Basophilia is a clue to chronic myeloid leukemia and other myeloproliferative disorders.
  • Systemic mastocytosis: clonal mast cells, often with a KIT mutation, with flushing and anaphylaxis episodes.

In the lab

  • Serum tryptase drawn soon after a suspected anaphylaxis supports the diagnosis.
  • Specific IgE in blood and skin-prick tests show sensitization (not always clinical allergy).
  • Basophil count in the differential.

Test yourself

Think of the answer, then tap the question to see it.

What triggers degranulation of a sensitized mast cell?

Cross-linking of IgE bound to FcεRI by a multivalent allergen.

Which preformed mediator in the blood helps confirm anaphylaxis?

Tryptase, released from mast cell granules.

How do mast cells and basophils differ in where they live?

Mast cells reside long-term in tissues; basophils circulate in the blood and are rare.

A high basophil count should make one think of which blood cancer?

Chronic myeloid leukemia (and other myeloproliferative disorders).

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← All of immunology

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: Mast Cells (British Society for Immunology, 2024); Basophils (British Society for Immunology, 2024); 18.4 Leukocytes and Platelets (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); Anaphylaxis (MedlinePlus, U.S. National Library of Medicine, 2024).

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Representative model, for educational purposes only.