Eosinophil

Eosinophils (≈ 12–15 µm) have a characteristically bilobed ("spectacle") nucleus and cytoplasm packed with large, refractile granules that stain bright orange-red with eosin. Each specific granule has a crystalloid core of major basic protein (MBP) surrounded by a matrix containing eosinophil cationic protein, eosinophil peroxidase and eosinophil-derived neurotoxin — all toxic to parasites and, unfortunately, to host epithelium. Eosinophils also make leukotriene C4, platelet-activating factor and cytokines.

They are produced in the marrow under the control of IL-5, circulate briefly (hours) and then reside in tissues — normally the lamina propria of the gut, and in disease the airways and skin — attracted by eotaxins (CCL11) and other chemokines. Helminths are far too large to be phagocytosed, so eosinophils bind IgE- or IgG-coated worms through Fc receptors and degranulate onto their surface (antibody-dependent cell-mediated cytotoxicity). In allergic disease, Th2 cytokines (IL-5, IL-4, IL-13) drive eosinophil recruitment in the late phase of the response, causing epithelial damage and airway remodelling in asthma.