Cytokine-induced airway epithelial ICAM-1 upregulation: quantification by high-resolution scanning and transmission electron microscopy.

The aim of this study was to investigate the variation of intercellular adhesion molecule (ICAM)-1 which occurs between individual airway epithelial cells of distinct phenotype. 16HBE14o- (16HBE) and BEAS-2B cell lines and human airway explants were cultured with medium alone or a mixture of tumour necrosis factor (TNF)-alpha (10 ng x mL(-1)) and interferon (IFN)-gamma (40 ng x mL(-1)) before being immunogold-labelled and examined quantitatively using sensitive high-resolution electron microscopic techniques. By enzyme-linked immunosorbent assay there was a 1.6-fold increase of ICAM-1 in the BEAS-2B cells following the cytokine mix which was not apparent in the 16HBE cells. However, high-resolution scanning electron microscopy demonstrated that an upregulation had occurred; median and ranges for gold particle number per 10 microm2 cell surface were: 7.9 (0-40) for nonstimulated and 19.1 (0-60 for stimulated) (p<0.01, Mann-Whitney U-test). The value for the nonstimulated BEAS-2B cells was 24.2 (0-60), 3-times higher that the constitutive expression in the 16HBE cells (p<0.01), whereas following stimulation, it was 68.5 (20-130) (p<0.01). Values for explant epithelial outgrowths were similar to the 16HBE cells. Immunohistochemistry of the explanted mucosa showed both constitutive and upregulated expression of epithelial ICAM-1 associated with basal and indeterminate cells rather than with ciliated or goblet cells. These results using high-resolution techniques indicate that there is marked cell-to-cell variation in cellular adhesion molecule expression and that it is the basal cells and less well differentiated (indeterminate) epithelial cells which are likely to play key roles in leukocyte retention via intercellular adhesion molecule-1.