Up-regulation by tumor necrosis factor alpha of intercellular adhesion molecule 1 expression and function in synovial fibroblasts and its inhibition by glucocorticoids.

OBJECTIVE: To examine the regulation of the intercellular adhesion molecule 1 (ICAM-1) gene in cultured human synovial fibroblasts in response to tumor necrosis factor alpha (TNF alpha), and investigate its modulation by the synthetic glucocorticoid, dexamethasone. METHODS: Cell surface expression of ICAM-1 was determined by flow cytometry, enzyme immunoassay, and immunoprecipitation. ICAM-1 messenger RNA (mRNA) levels were monitored by Northern blot. ICAM-1 function was determined by measuring the adhesion of monocytes to synovial fibroblasts. RESULTS: ICAM-1 expression on unstimulated cells was weak but was rapidly enhanced in both a time- and dose-dependent manner following exposure to TNF alpha. Treatment of the cells with TNF alpha also resulted in both a time- and dose-dependent increase in steady-state ICAM-1 mRNA levels, as determined by Northern blot. The increased expression of ICAM-1 was inhibited by cycloheximide and actinomycin D. Cultured synovial fibroblasts from patients with rheumatoid and nonrheumatoid arthropathies responded similarly to TNF alpha. Adhesion studies demonstrated that ICAM-1 is involved in the adherence of peripheral blood monocytes to TNF alpha-activated synovial fibroblasts. In addition, dexamethasone inhibited TNF alpha-induced surface expression of ICAM-1, accumulation of ICAM-1 mRNA, and adhesion of monocytes to TNF alpha-activated synovial fibroblasts. CONCLUSION: These combined results provide further evidence of an important role of ICAM-1 in inflammatory synovitis, as well as a potentially novel site of antiinflammatory action of glucocorticoids.

Inhibition of lymphocyte adhesion to cytokine-activated synovial fibroblasts by glucocorticoids involves the attenuation of vascular cell adhesion molecule 1 and intercellular adhesion molecule 1 gene expression.

OBJECTIVE: The aim of this study was to evaluate the ability of glucocorticoids to inhibit lymphocyte adhesion to human synovial fibroblasts. METHODS: Adhesion of lymphocytes to cultured synovial fibroblasts was measured by counting the number of cells bound to fibroblasts. Surface expression of intercellular adhesion molecule 1 (ICAM-1) was measured by enzyme-linked immunosorbent assay, while vascular cell adhesion molecule 1 (VCAM-1) surface expression was measured by flow cytometry. ICAM-1 and VCAM-1 messenger RNA (mRNA) levels were assessed by Northern blot analysis. RESULTS: Stimulation of synovial fibroblasts by the proinflammatory cytokines tumor necrosis factor alpha, interleukin-1beta, and interferon-gamma resulted in a dose-dependent increase in lymphocyte adhesion to synovial fibroblasts. This response was inhibited by preincubation of the cells with the synthetic glucocorticoid dexamethasone. Since lymphocyte adhesion to synovial fibroblasts is known to be mediated by VCAM-1 and ICAM-1, we examined the modulation of VCAM-1 and ICAM-1 expression in these cells. All 3 cytokines stimulated VCAM-1 and ICAM-1 surface and mRNA expression. Dexamethasone inhibited both VCAM-1 and ICAM-1 surface and mRNA expression in a dose-dependent manner, which correlated with the inhibition of lymphocyte adhesion. CONCLUSION: Taken together, these results suggest that glucocorticoids may reduce inflammatory responses at extravascular sites by inhibiting the expression of these adhesion molecules, thereby reducing the adhesion of lymphocytes to connective tissue cells.