Basophils are a type of white blood cell of the innate immune system. Basophils are granulocytes named for their basophilic granules (stain blue on H&E). Degranulation or release of the molecules inside granules occurs in response to the binding of IgE antibodies. Importantly, three molecules released from basophil granules are histamine, heparin, and leukotrienes. Ultimately, the release of these compounds promotes inflammation to fight parasitic infections. However, erroneous activation of basophils contributes to allergic/anaphylactic reactions. Finally, elevated basophil counts may be a diagnostic sign of chronic myelogenous leukemia (CML).

Key Points

  • Basophils
    • White blood cell of the innate immune system
    • Contains granules that are basophilic (blue) on the H&E stain
    • Activate after binding to Immunoglobulin E (IgE)
      • via Fc-epsilon receptors, which bind to the Fc-region of IgE
      • Close proximity of IgE causes Fcε receptor aggregation, leading to degranulation
    • Activation leads to the release of:
      • Histamine
      • Heparin
      • SRS (slow-reacting substance of anaphylaxis), a mix of leukotrienes
    • Mediates allergy/anaphylaxis, similar to mast cells
      • Also called Type I Hypersensitivity Reactions
    • Elevated basophils may be a sign of Chronic Myelogenous Leukemia (CML)