MECHANISMS OF EOSINOPHIL RECRUITMENT

As with other types of leukocytes, mechanisms that function to enable the recruitment of eosinophils into specific sites of immune reactions involve a complex and cumulative interplay of many molecules and path ways. No single chemoattractant is specific for eosinophils, but rathe r various chemoattractants active on eosinophils can also elicit migra tion of other specific cell types. Humoral mediators causing eosinophi l migration include C5a and platelet-activating factor, whereas cytoki nes active as eosinophil chemoattractants include interleukin (IL)-2, IL-3, IL-5, granulocyte/macrophage colony-stimulating factor, lymphocy te chemoattractant factor, and RANTES. Eosinophils utilize several pat hways to adhere to vascular endothelial cells, including binding to in tercellular adhesion molecule-1, E-selectin, and vascular cell adhesio n molecule-1 (VCAM-1). The lack of binding of neutrophils to VCAM-1 an d the enhanced expression of VCAM-1 elicited by IL-4 contribute to pre ferential eosinophil accumulation. Eosinophil recruitment is dependent not only on ligands expressed on eosinophils and molecules inducible on endothelial cells but also on processes active during transendothel ial migration and extravascular migration in the extracellular spaces.