Inhibitory effect of retinoids on the generation of procoagulant activity by blood mononuclear phagocytes.

Retinoids are known to modulate several functions of mononuclear phagocytes. We have studied the effect of retinyl acetate (RAc) and retinoic acid (RA) on the production of procoagulant activity (PCA) by human peripheral blood mononuclear cells stimulated with endotoxin (1 microgram/ml, 4 or 20 h at 37 degrees C). Both compounds caused a dose-dependent reduction in the expression of cell-associated PCA (from 86 to less than 10% of control in the range of concentration comprised between 0.1 and 100 microM). This effect was also observed when the cells were exposed to retinoids for 10 min and washed before challenge with endotoxin, indicating that it is rapid and irreversible. In contrast, incubation of RAc or RA for 3 h at 37 degrees C with cells that have been already stimulated with endotoxin (20 h at 37 degrees C) remained without influence on cell PCA. The inhibitory action of retinoids was also observed when monocyte-enriched (greater than 85%) preparations or highly purified monocyte-derived macrophages (greater than 99%) were used instead of whole mononuclear cells. BW755C, an inhibitor of cyclo-oxygenase and lipoxygenase, reversed the inhibitory effect of retinoids, whereas acetylsalycilic acid, an inhibitor of cyclo-oxygenase, was inactive, suggesting the involvement of a lipoxygenase product. The inhibition of monocyte/macrophage PCA production and the subsequent reduction of cell potential for fibrin deposition might represent one of the mechanisms whereby retinoids exert their antiinflammatory and immunomodulatory activities.