Agents that downregulate the induction of monocyte/macrophage tissue factor (TF) activity may attenuate the thrombotic risk associated with mechanical restoration of vessel patency or artificial arterial grafting. In such events, procoagulant macrophages in the atherosclerotic plaque and procoagulant monocytes adherent to artificial materials may be exposed to the blood stream. Ishii et al (Blood 80:2556, 1992) reported that induction of endothelial TF is downregulated by all-trans retinoic acid (ATRA), and Conese et al (Thromb Haemost 66:662, 1991) reported that retinoids downregulate monocyte procoagulant activity (PCA). These findings led us to investigate the effect of ATRA on monocyte TF expression, and to study the effect of ATRA on monocyte-induced thrombus formation in a model system of human arterial thrombogenesis. Induction of PCA in human peripheral blood monocytes by 0.5 microgram/mL lipopolysaccharide (LPS) was dose dependently reduced by ATRA, reaching a reduction of 56% at 10(-5) mol/L ATRA (P < .0001). A 38% reduction (P < .0007) in LPS-induced TF antigen expression was observed at an ATRA concentration of 10(-6) mol/L. Adherence of monocytes to plastic cover slips (Thermanox, Miles Laboratories, Naperville, IL) also triggered induction of cellular PCA, which was inhibited by more than 80% by an anti-TF monoclonal antibody (MoAb) (P < .002). Inclusion of ATRA (10(-6) mol/L) reduced this PCA by 40% (P < .03), and the TF antigen expression by 30% (P < .0001). Exposure of Thermanox adherent monocytes to flowing nonanticoagulated human blood in a parallel-plate perfusion chamber device at an arterial wall shear rate of 650 s-1 elicited significant fibrin deposition and platelet thrombus formation. Partial interruption of this thrombus formation was achieved by 10(-6) mol/L ATRA, which reduced the fibrin deposition by 80% (P < .02) and platelet thrombus formation by 50% (P < .05). In comparison, incubation of adherent monocytes with the anti-TF MoAb before the blood exposure, reduced the fibrin deposition by 83% (P < .02) and platelet thrombus volume by 75% (P < .0008). Thus, ATRA is an effective down-regulator of monocyte TF-PCA, and may reduce thrombotic complications at sites of plaque rupture, at plaque disruption after percutaneous transluminal angioplasty procedures, or on surfaces introduced by artificial arterial grafting.