Intercellular Interactions in the Recruitment and Functions of Human Eosinophils

Intercellular interactions amongst eosinophils and adjacent cells are involved in the recruitment and functioning of eosinophils within tissues. For their mobilization from the vasculature and adherence to endothelial cells, eosinophils utilize mechanisms dependent on CD18 as well as on binding to either endothelial leukocyte adhesion molecule-1 or vascular cell adhesion molecule-1 (VCAM). Eosinophils, unlike neutrophils, express VLA-4, the ligand mediating adhesion to VCAM. Eosinophil recruitment is also promoted by lymphokines, including lymphocyte chemoattractant factor (LCF) and interleukin-2 (IL-2), both of which are about 1,000 times more potent than either PAF or C5a as eosinophil chemoattractants. As on lymphocytes and monocytes, LCF utilizes CD4 on eosinophils as its receptor; and IL-2 stimulated migration is mediated by apparent high affinity IL-2 receptors on eosinophils. Eosinophils recruited into tissues may have multiple functional capabilities, including the capacity to elaborate cytokines active on other cells, including TGF-α, TGF-β1 and IL-1α, and the capacity to serve as MHC-restricted, HLA-DR-dependent antigen-presenting cells to stimulate proliferative responses of CD4+ lymphocytes.