Stimulation of Monocyte Procoagulant Activity by Adherence to Different Surfaces

When mononuclear leukocyte suspensions (5.109 cells/1, 25% monocytes) were incubated on glass dishes, 57 ± 1% of the monocytes were found to adhere to the surface after 3.5 h incubation at 37°C. It was found that the adherent cells shortened the recalcification time from 435 ± 35 to 50 + 2 sec using normal plasma as substrate. However, when monocyte adherence was prevented by incubating the leukocytes on cuprophane (3 + 1% adherence), much less PCA was detectable (the recalcification time was shortened from 435 ± 35 to 201 ± 19 sec). After exposing to glass the non-adherent monocytes had negligible PCA in comparison to the adherent monocytes. Protein synthesis inhibitors (cycloheximide and actinomycin D) inhibited PCA generation but did not affect monocyte adherence. These data provide the first evidence that adherence of monocytes is a stimulus for the generation of thromboplastic activity.