| Abstract: | Objective. 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. Methods. 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. Results. Treatment of HSE with interleukin-1α (IL-1α) or tumor necrosis factor α (TNFα) 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-γ (IFNγ) greatly potentiated the increase in ICAM-1 surface expression. The synergistic effect of IFNγ 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. IFNγ also augmented the actions of several other agonists on HSE, i.e., IL-4, lipopolysaccharide, and TNFβ/lymphotoxin. Immunoprecipitation of TNFα + IFNγ–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, IFNγ alone was a potent stimulus for HSE ICAM-1 mRNA synthesis, but was relatively ineffective in HUVE. Conclusion. These studies indicate that IFNγ plays a critical synergistic role in the regulation of ICAM-1 expression in human synovial endothelial cells. |
