Monocyte-associated tissue factor is suppressed by phorbol myristate acetate

Area of Science:

• Hematology
• Cell Biology
• Immunology

Background:

• Monocytes are key circulating cells initiating blood coagulation through tissue factor (TF) expression.
• Isolated monocytes can be stimulated to express TF activity by various agents.
• TF expression is crucial for hemostasis and thrombosis.

Purpose of the Study:

• To investigate the modulatory effects of phorbol myristate acetate (PMA) on monocyte tissue factor (TF) expression and activity.
• To understand the relationship between PMA-induced cellular events and TF modulation in monocytes.

Main Methods:

• Isolated human peripheral blood monocytes were treated with adherence, endotoxin, and varying concentrations of PMA.
• Monocyte tissue factor activity was measured.
• Protein kinase C (PKC) translocation and oxygen metabolite release were assessed.
• Immunofluorescent staining using anti-human TF monoclonal antibody (MoAb) HTF1-7B8 was performed.

Main Results:

• Adherence and endotoxin treatment increased monocyte tissue factor activity and antigen expression.
• Low-dose PMA (10(-11) to 10(-12) mol/L) enhanced TF activity.
• High-dose PMA (10(-9) to 10(-7) mol/L) decreased adherence- and endotoxin-induced TF activity and antigen.
• High-dose PMA induced PKC translocation and oxygen metabolite release in a time- and dose-dependent manner.

Conclusions:

• Monocyte TF expression is differentially regulated by various stimuli.
• PMA exhibits dual effects on monocyte TF activity, enhancing it at low doses and suppressing it at high doses.
• High-dose PMA-mediated suppression of TF is linked to PKC activation and oxygen metabolite production.