To examine the regulation of intercellular adhesion molecule 1 (ICAM-1) in human synovial microvascular endothelial cells (HSE) and human umbilical vein endothelial cells (HUVE) upon exposure to a variety of agents.
Cultured endothelial cells were treated with various cytokines alone and in combination. The expression of ICAM-1 was evaluated at several levels, including an investigation of messenger RNA (mRNA) and surface protein expression.
Treatment of HSE with interleukin-1 alpha (IL-1 alpha) or tumor necrosis factor alpha (TNF alpha) resulted in minimal increases in ICAM-1 expression, in contrast to findings with HUVE. Incubation of HUVE or HSE with IL-1 or TNF in combination with interferon-gamma (IFN gamma) greatly potentiated the increase in ICAM-1 surface expression. The synergistic effect of IFN gamma and TNF was confirmed by several methods, including a cell-based enzyme-linked immunosorbent assay, fluorescence-activated cell sorting, immunofluorescence staining, and determination of mRNA levels. IFN gamma also augmented the actions of several other agonists on HSE, i.e., IL-4, lipopolysaccharide, and TNF beta/lymphotoxin. Immunoprecipitation of TNF alpha + IFN gamma-stimulated, 125I-labeled HSE cells with anti-ICAM-1 revealed a single 90-kd band, similar in size to ICAM-1 from HUVE treated in an identical manner. Unexpectedly, IFN gamma alone was a potent stimulus for HSE ICAM-1 mRNA synthesis, but was relatively ineffective in HUVE.
These studies indicate that IFN gamma plays a critical synergistic role in the regulation of ICAM-1 expression in human synovial endothelial cells.