Subthreshold hyperoxia potentiates TNF-alpha-induced ICAM-1 expression on cultured pulmonary microvascular...

The effects of combined exposure to subthreshold hyperoxia and the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) on the expression of intercellular adhesion molecule-1 (ICAM-1) were examined in bovine lung microvascular endothelial cells (BLuEC). The expression of total ICAM-1 was not affected by 50% hyperoxia conditions alone, indicating that this level is subthreshold for BLuEC. In the presence of 5 ng/mL TNF-alpha, which has minimal influence on BLuEC alone, the amount of total ICAM-1 expression under 50% hyperoxia was higher than that in normoxic conditions (approximately 30%) throughout the culture period. The amount of soluble ICAM-1 that has been released into the culture medium increased after joint exposure to hyperoxia and TNF-alpha. These results suggest that exposure to subthreshold hyperoxia, which does not by itself cause damage to the endothelial cells or induce ICAM-1 expression, potentiates the effects of low-level TNF-alpha exposure.