Ligation of intercellular adhesion molecule 3 inhibits GM-CSF production by human eosinophils

Background: Intercellular adhesion molecule 3 (ICAM-3) has recently been identified on the surface of eosinophils. Objective: The purpose of this study was to characterize ICAM-3 expression on eosinophils in response to cytokines and to determine whether ligand binding of ICAM-3 modulates inflammatory responses of eosinophils, as it does in other leukocytes. Methods: To determine effects of ICAM-3 on eosinophil function, we isolated human eosinophils and used a monoclonal antibody directed against the epitope of ICAM-3 that binds to leukocyte-function antigen-1 to mimic binding of ICAM-3 and this natural ligand. We measured granulocyte-macrophage colony stimulating factor (GM-CSF) production by unstimulated eosinaphils; and eosinaphils stimulated with ionomycin (1 mumol/L), both in the presence and absence of this anti-ICAM-3 antibody. Results: We found that 99% of eosinophils expressed ICAM-3, regardless of whether allergic symptoms were present or absent. Expression of ICAM-3 was not enhanced by proinflammatory cytokines. Expression of ICAM-3 was reduced in apoptotic cells and in cells incubated with the combination of GMCSF and tumor necrosis factor-alpha (n = 3). Antibody binding of ICAM-3, which mimics leukocyte-function antigen-1 binding, had no effect on baseline GM-CSF production but reduced by 80% the production of GM-CSF stimulated by ionomycin (control 1969 pg/mL +/- 1259 SD versus anti-ICAM-3 396 pg/mL +/- 207 SD, n = 8) and reduced GM-CSF mRNA content. Conclusions. ICAM-3 is highly expressed on the surface of human eosinophils, and downregulation of GM-CSF production by anti-ICAM-3 mAb suggests that ICAM-3 ligation may inhibit eosinophil inflammatory responses and survival.