TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA)-INDUCED CELL-ADHESION TO HUMAN ENDOTHELIAL-CELLS IS UNDER DOMINANT CONTROL OF ONE TNF RECEPTOR TYPE, TNF-R55

Tumor necrosis factor alpha (TNF-alpha) is a pleiotropic cytokine trig gering cell responses through two distinct membrane receptors. Stimula tion of leukocyte adhesion to the endothelium is one of the many TNF-a lpha activities and is explained by the upregulation of adhesion molec ules on the endothelial cell surface. Human umbilical vein endothelial cells (HUVEC) were isolated, cultured, and demonstrated to express bo th TNF receptor types, TNF-R55 and TNF-R75. Cell adhesion to HUVEC was studied using the HL60, U937, and MOLT-4 cell lines. HUVEC were activ ated by either TNF-alpha, binding to both TNF-R55 and TNF-R75, and by receptor type-specific agonists, binding exclusively to TNF-R55 or to TNF-R75. The TNF-alpha-induced cell adhesion to HUVEC was found to be controlled almost exclusively by TNF-R55. This finding correlated with the exclusive activity of TNF-R55 in the TNF-alpha-dependent regulati on of the expression of the intercellular adhesion molecule type 1 (IC AM-1), E-selectin, and vascular cell adhesion molecule type 1 (VCAM-1) . The CD44 adhesion molecule in HUVEC was also found to be upregulated through TNF-R55. However, both TNF-R55 and TNF-R75 upregulate alpha2 integrin expression in HUVEC. The predominant role of TNF-R55 in TNF-a lpha-induced adhesion in HUVEC may correlate with its specific control of NF-kappaB activation, since kappaB elements are known to be presen t in ICAM-1, E-selectin, and VCAM-1 gene regulatory sequences.