Increased CD44 expression in human bronchial epithelial repair after damage or plating at low cell densities

We have investigated the effect of mechanical damage, cell density, and cel l-derived soluble mediators on CD44 expression in a model of bronchial epit helial repair. CD44 (all isoforms) and variant-containing isoforms (CD44v3, CD44v6, and CD44v9) were identified with flow cytometry and immunocytochem istry with image analysis. After mechanical damage, CD44 expression increas ed up to 500 mu m from the wound edge and for up to 48 h in two human bronc hial epithelium-derived cell lines, 16HBE14o- and NCI-H292. CD44 expression was unchanged by interferon-gamma and increased by <50% by tumor necrosis factor-alpha. To exclude other soluble factors, a Vaseline spacer was used to temporarily divide petri dishes, with cells at high density on one side and those at low density on the other. After the spacer was removed, the ce lls at low cell density growing in the shared medium expressed up to fourfo ld higher CD44, although cell proliferation was unchanged. Thus increased C D44 expression at low cell density was not mediated by soluble factors and may reflect functional involvement in cell motility, dedifferentiation, or altered cell-substrate adhesion in epithelial repair.