Basophilic granulocytes or ‘basophils’ are a type of leucocyte (‘white blood cell’) that circulates in the blood. They are the rarest of the granulocytes (the others are neutrophils and eosinophils), usually representing less than 0.5% of leucocytes in the peripheral blood of humans or mice. Basophils can participate in the expression of acute and chronic and allergic diseases, including anaphylaxis, asthma, atopic dermatitis and hay fever. Basophils also can contribute to resistance to internal parasites (such as helminths) and ectoparasites (such as ticks). At a steady state, upon leaving the bone marrow, basophils reside mainly in the peripheral blood but can migrate into tissues such as lymph nodes, skin and the lungs where they can play roles in regulating immune responses or in the pathogenesis of diseases. When they participate in allergic reactions or responses to parasites, basophils release histamine and many other biologically active molecules that can contribute to inflammation.

Key Concepts:

  • Basophils are the rarest granulocytes circulating in the peripheral blood.

  • Basophils are increased during inflammatory responses such as certain types of skin inflammation, asthma or parasite infections, settings in which basophils may appear in the affected tissues.

  • Basophils are activated when antigen‐specific IgE antibodies that may recognise antigens derived from parasites or from substances that cause allergies (such as ragweed allergens in subjects with hay fever induced by ragweed) that are bound to the basophils' high‐affinity IgE receptors (FcɛRI) encounter bi‐ or multivalent antigen recognised by that FcɛRI‐bound IgE.

  • Basophils activated by IgE and antigen can help to induce the development of acute allergic reactions, such as anaphylaxis to bee stings or peanut products, and also chronic allergic reactions, such as in asthma or atopic dermatitis.

  • Basophils have common features with mast cells (which are normally located in the tissues, but, unlike basophils, are not normally present in the blood), and basophils and mast cells can play similar or overlapping roles, as well as have some distinct roles, in the induction of allergic diseases or in immune responses against parasites or ticks.

  • Chronic myelogenous leukaemia patients often have a markedly increased number of basophils in the blood and bone marrow.

Keywords: allergy; asthma; immunoglobulin E; mast cells; parasites

Figure 1.

Transmission electron micrograph (osmium collidine uranyl en bloc processing) showing a mast cell (M) and basophil (B) in the ileal submucosa of a patient with Crohn's disease. The mast cell is the larger, mononuclear cell; it has more complex plasma‐membrane surface and cytoplasmic granules (arrowheads) that are smaller and more numerous than those (arrows) of the basophil. In this section plane, the basophil has two nuclear lobes (n). Several basophil cytoplasmic granules are visible that contain whorls of membrane (curved arrows). Reprinted from Dvorak et al. , with permission from Elsevier. © (1980).

Figure 2.

Basophils develop from haematopoietic stem cells in the bone marrow, where they typically complete their differentiation/maturation. They then leave the bone marrow and circulate as mature granulocytes in the peripheral blood. Basophils can be recruited to enter tissues at sites of immunological or inflammatory reactions in response to the local generation of certain lipid mediators, cytokines and/or chemokines (which can be released from mast cells and many other cell types). Increased levels of IgE antibodies, which are found in subjects with allergic diseases or parasite infections, can induce upregulation of surface expression of FcɛRI on basophils (and mast cells), priming such cells to release increased amounts of mediators after allergen/antigen crosslinking of surface‐bound, allergen/antigen‐specific IgE. In subjects ‘sensitised’ by an initial exposure to antigens/allergens derived from parasites (e.g. ticks or worms) or environmental agents (e.g. pollen or insect venom), plasma cells produce antigen/allergen‐specific IgE antibodies (this is an acquired immune response involving T helper type 2 (TH2) cells). In such ‘sensitised’ hosts, basophil degranulation/activation can be induced in response to any antigens/allergens against which the host has developed IgE, including those derived from feeding ticks, worms or environmental agents such as pollen, food or drugs. Systemic degranulation/activation of basophils in the blood (e.g. in response to certain components of medicines, insect venoms or foods) can contribute to systemic anaphylaxis. Other pathways of basophil activation exist (e.g. by viral products), but are not shown in the diagram (see text). Cytokine release from basophils (e.g. IL‐4 and IL‐13) may have immunoregulatory effects (e.g. by contributing to enhanced IgE production). *Several lines of evidence suggest that basophils are derived from the common myeloid progenitor. Mast cells, T cells and many other cell types can secrete products that can enhance basophil adhesion, migration and function. The term ‘allergens’ is usually used to refer to antigens that can elicit TH2 responses in at least some individuals. Accordingly, IgE antibodies participate in the pathology of certain allergies as well as in host defence against some parasites. §TH2 cells also represent a source of IL‐3 resulting in increased numbers of basophils in the blood and the bone marrow.



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Further Reading

Galli SJ, Kalesnikoff J, Grimbaldeston MA et al. (2005) Mast cells as “tunable” effector and immunoregulatory cells: recent advances. Annual Review of Immunology 23: 749–786.

Karasuyama H, Mukai K, Obata K, Tsujimura Y and Wada T (2011) Nonredundant roles of basophils in immunity. Annual Review of Immunology 29: 45–69.

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Siracusa MC, Comeau MR and Artis D (2011) New Insights into basophil biology: initiators, regulators, and effectors of type 2 Inflammation. Annals of the New York Academy of Science 1217: 166–177.

Sullivan BM and Locksley RM (2009) Basophils: a nonredundant contributor to host immunity. Immunity 30(1): 12–20.

Wedemeyer J, Tsai M and Galli SJ (2000) Roles of mast cells and basophils in innate and acquired immunity. Current Opinion in Immunology 12: 624–631.

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Mukai, K, and Galli, SJ(Jun 2013) Basophils. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001120.pub3]