Biomaterials activate leukocytes as well as platelets when exposed to blood. One feature of leukocyte activation at least at times beyond a few hours is tissue factor expression, contributing to a procoagulant state. We show here that platelet activation and specifically platelet-monocyte aggregate formation appears to be a precondition for tissue factor expression. Material-induced Tissue Factor (TF) expression by isolated leukocytes (6 x 10(6) cells/mL) resuspended in increasing concentrations of platelets in plasma was elevated when the platelet concentration was 50 x 10(6) platelets/mL or more; at lower platelet concentrations (1-25 x 10(6). cells/mL) the TF expression remained at background levels. On the other hand, significant @entity9536 upregulation was observed on leukocytes, in bulk and adherent to beads, at all platelet concentrations. This platelet effect on material-induced TF expression appeared to be mediated by the formation of platelet-monocyte aggregates. Anti- @entity8729 , which blocked the association between platelets and leukocytes, reduced monocyte adhesion and material-induced TF expression for bulk monocytes. Anti- @entity1427 /IIIa, a @entity1427 /IIIa platelet antagonist, also reduced monocyte adhesion and material-induced TF expression in the bulk, most likely due to its inhibiting effect on the formation of platelet-monocyte aggregates, secondary to platelet activation. However, the antibody-associated reductions for bulk leukocytes (mainly neutrophils) were small and incomplete. Similar levels of TF expression, in the bulk, were observed with both @entity852 (PS), a strong platelet activator, and @entity968 -modified @entity970 (PS- @entity970 ), a mild platelet activator. The role of platelets in material-induced TF expression appears to be mediated in part via the formation of platelet-monocyte aggregates, although other mechanisms are likely also involved.

Material-induced tissue factor expression but not XXXX upregulation depends on the presence of platelets.

@entity852 :: ('MESH:D011137', 'Chemical') :: ['polystyrene'] @entity8729 :: ('6403', 'Gene') :: ['P-selectin'] @entity1427 :: ('3674', 'Gene') :: ['GPIIb'] @entity9536 :: ('3684', 'Gene') :: ['CD11b'] @entity970 :: ('CHEBI:46793', 'Chemical') :: ['PEG'] @entity968 :: ('MESH:D011092', 'Chemical') :: ['polyethylene glycol']
@entity9536 :: (3684,Gene) :: ['CD11b']
