CorpusHuman Anatomy
Lymphatic & ImmuneCell

Basophil

Granulocytus basophilus

Also known as: basophilic granulocyte, baso

The rarest leukocyte (< 1%): a granulocyte whose large dark-purple granules, rich in histamine and heparin, obscure its nucleus; it binds IgE and releases mediators of allergic inflammation.

Overview

Proportion of leukocytes< 1% (≈ 0.5–1%)
Normal count0.01–0.1 × 10⁹/L

Basophils are ≈ 10–14 µm granulocytes with a bilobed or S-shaped nucleus usually hidden by coarse, dark blue-purple metachromatic granules containing histamine, heparin and other proteoglycans. Like mast cells they express the high-affinity IgE receptor FcεRI; when bound IgE is cross-linked by allergen they degranulate and rapidly synthesise leukotriene C4 and the Th2 cytokines IL-4 and IL-13.

Basophils and mast cells are functionally similar but distinct cells: basophils mature in the marrow, circulate, live only days and are recruited into tissues during allergic and parasitic inflammation, whereas mast cells mature in tissues and live for months. Basophils contribute to the late phase of allergic reactions, to anaphylaxis and to defence against ticks and helminths, and are an early source of IL-4 that pushes T cells towards Th2.

Location

Blood; recruited into inflamed tissues (allergic skin, airways).

Function

  • Release histamine, heparin and leukotrienes in allergic reactions (type I hypersensitivity).
  • Early source of IL-4 and IL-13, promoting Th2 responses and IgE class switching.
  • Contribute to defence against helminths and ectoparasites.
Physiology

Normal count 0.01–0.1 × 10⁹/L. Activated by IgE cross-linking, complement C3a/C5a and IL-3, which is also their main growth factor.

Clinical significance

Basophilia

A raised basophil count is a classic clue to chronic myeloid leukaemia and other myeloproliferative neoplasms; it also occurs in hypothyroidism and some allergic and inflammatory states. The basophil activation test (flow cytometry for CD63 after allergen exposure) is used in allergy diagnosis.

Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.