Differential expression of human corneal and perilimbal ICAM-1 by inflammatory cytokines

The mechanisms that regulate corneal infiltration by circulating leukocytes in inflammatory diseases are poorly understood. In this study, we investigated the effects of pro-inflammatory cytokines on corneal endothelial (CE) and stromal (CS) expression of intercellular adhesion molecule-1 (ICAM-1), a specialized cell surface glycoprotein that binds the leukocyte function antigen-1 (LFA-1) receptor present on all leukocytes and enhances immune responses. Using specific monoclonal antibody (mAb) to ICAM-1, immunohistochemical staining of intact human corneas resulted in discrete, granular reaction product in CE and CS cells as well as perilimbal vascular endothelium that increased dramatically when exposed to human recombinant interleukin-1-beta (rIL-1 beta), tumor necrosis factor-alpha (rTNF-alpha), and interferon-gamma (rIFN-gamma). Immunoreactive ICAM-1 in CE and CS cells was differentially increased by each of these cytokines. In contrast, immunoreactive endothelial-leukocyte adhesion molecule-1 and vascular cell adhesion molecule-1 were not detected in any CE or CS cells of unstimulated or cytokine-stimulated corneas. In standardized leukocyte adherence assays, neutrophil binding to CE surfaces of whole corneas increased significantly upon exposure to rIL-1 beta, rTNF-alpha, or rIFN-gamma (P less than 0.001). In parallel assays, mAb to ICAM-1 on CE cells or subunits of LFA-1 receptors on leukocytes, but not control mAb, significantly blocked leukocyte binding to unstimulated (P less than 0.01) or rIFN-gamma-stimulated corneas (P less than 0.001). Our results indicate that: (1) ICAM-1 is expressed at low levels on unstimulated CE cells, CS cells, and perilimbal vascular endothelium; (2) ICAM-1 may be augmented differentially in corneal and perilimbal tissue by pro-inflammatory cytokines; and (3) ICAM-1 is a functional ligand mediating corneal-leukocyte binding. Differential expression of ICAM-1 within corneal tissue may regulate keratitic precipitate formation, leukocyte trafficking and accumulation, and localized generation of immune responses.