CELLS

Basophils represent the least abundant white blood cells in human blood with a normal range of 1–2% of all circulating leukocytes.^1,2 They are generated from the multipotent, lineage-restricted granulocyte–monocyte progenitors in the bone marrow where they eventually differentiate into basophils or mast cell precursors. Increased expression of C/EBPα and concomitant reduction of GATA-2 in the granulocyte-monocyte progenitor cells may facilitate basophil differentiation. Absence of Ikaros is also associated with profound expression of basophils. Basophils are short-lived and after differentiation, they populate the periphery as fully mature cells.¹

Basophils have both pro-inflammatory and anti-inflammatory functions. Basophils express a wide variety of G-protein–coupled and non-G-protein–coupled receptors for chemokines or other chemotactic factors.³ Basophils are activated by a variety of stimuli including cytokines (eg, IL-3, IL-18, IL-33, TSLP), protease allergens (eg, house dust mite protease), and environmental stimuli (eg, drugs, venoms, pollens).⁴ Upon activation, basophils can rapidly produce IL-4 and IL-13, release histamine and leukotriene C⁴ and express CD40 ligand which stimulates IgE class switching in B cells.³ Basophils function as an important contributor to the inflammatory reactions during immune response, as well as to autoimmune and inflammatory disorders, development of acute and chronic allergic diseases, asthma, and cancer.^3,4

BaP: basophil precursor; BMCP: basophil-mast cell precursor; C/EBPα: CCAAT-enhancer-binding protein alpha; CD: cluster of differentiation; GATA-2: GATA-binding protein 2; Ig: immunoglobulin; IL: interleukin; MCp: mast cell precursor; TSLP: thymic stromal lymphopoietin.