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. Author manuscript; available in PMC: 2012 Aug 21.
Published in final edited form as: Immunol Allergy Clin North Am. 2009 Feb;29(1):129–xi. doi: 10.1016/j.iac.2008.10.004

Fig. 1.

Fig. 1

Eosinophil function in GI inflammation. Eosinophils are bilobed granulocytes with eo-sinophilic staining of secondary granules. The secondary granules contain four primary cationic proteins: eosinophil peroxidase (EPO), major basic protein (MBP), eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN). All four proteins are cytotoxic molecules; in addition, ECP and EDN are ribonucleases. Eosinophils can be activated by immune stimulus by way of toll-like receptor (TLR), immunoglobulin, and complement. In addition to releasing their preformed cationic proteins, eosinophils can also release a variety of cyto-kines, chemokines, lipid mediators, and neuromodulators. Eosinophils activate T cells by serving as antigen-presenting cells. Eosinophils can also regulate T-cell polarization through synthesis of indoleamine 2,3-dioxygenase (IDO), an enzyme involved in oxidative metabolism of tryptophan, catalyzing the conversion of tryptophan to kynurenines (KYN), a regulator of T helper cell type 1 and 2 balance. Eosinophils generate an array of cytokines, chemokines, lipid mediators, and neuromodulators that regulate leukocyte trafficking, activation, and maturation; adhesion system expression; collagen synthesis; cellular proliferation; and mucus cell hypersecretion. Eosinophils can also act as an end-stage effector cell, secreting cationic proteins that can regulate mast cell function and generate reactive oxygen species (ROS), reactive nitrogen species (RNS), epithelial cell injury, and muscarnic receptor (M2 and M3) dysfunction. FcR, Fc receptor; GM-CSF, granulocyte-macrophage colony–stimulating factor; IFN, interferon; IL, interleukin; LT, leukotriene; MHC, major histo-compatibility complex; MIP, macrophage inflammatory protein; PG, prostaglandin; RANTES, regulated on activation normal T-cell expressed and secreted; TGF, transforming growth factor; TNF, tumor necrosis factor; VIP, vasoactive intestinal peptide. (Adapted from Rothen-berg ME, Hogan SP. The eosinophil. Annu Rev Immunol 2006;24:149; with permission.)