Dynamics of leukocyte-platelet adhesion in whole blood

Abstract

The dynamics of leukocyte-platelet adhesion and platelet-platelet interaction in whole blood are not well understood. Using different platelet agonists, we have studied the whole blood kinetics of these heterotypic and homotypic interactions, the relative abilities of different leukocyte subsets to participate in platelet adhesion, and the ligands responsible for adhesion. When platelet aggregation was inhibited by the Arg-Gly-Asp-Ser (RGDS) peptide, thrombin stimulation of whole blood resulted in platelet expression of granule membrane protein 140 (GMP-140) and, simultaneously, a marked increase in the percentage of monocytes and neutrophils (PMN) binding platelets, as well as an increase in the number of platelets bound per monocyte and PMN. Lymphocytes were unaffected. Monocytes bound more platelets and at an initially faster rate than PMN. This increase in monocyte and PMN adhesion to platelets was completely inhibited by the blocking monoclonal antibody (MoAb), G1, to GMP-140. When the combination of epinephrine and adenosine diphosphate (epi/ADP) was used as a less potent agonist in the presence of RGDS, GMP-140 expression per platelet was less, and while monocyte-platelet conjugates formed, PMN-platelet conjugates did not. With epi/ADP in the absence of RGDS, there was an immediate, marked decrease in the percentage of all leukocytes with bound platelets, simultaneous with an increase in the percentage of unbound platelet aggregates. As these platelet aggregates dissociated, the percentage of monocytes and PMN with adherent platelets increased, with monocytes again binding at a faster initial rate than PMN. This recovery of monocyte and PMN adhesion to platelets was also inhibited by the G1 MoAb. We conclude that: (1) monocytes and PMN bind activated platelets in whole blood through GMP-140; (2) monocytes have a competitive advantage over PMN in binding activated platelets, particularly when less potent platelet agonists are used; and (3) platelet aggregate formation initially competes unactivated platelets off leukocytes; subsequent aggregate dissociation allows the now activated platelets to readhere to monocytes and PMN through GMP-140. These studies further elucidate the dynamic interaction of blood cells and possible links between coagulative and inflammatory processes.

Bimodal distribution of proteinase 3 (PR3) surface expression reflects a constitutive heterogeneity in the polymorphonuclear neutrophil pool

“…Both the origin of membrane PR3 and the interaction be-tween PR3 and the neutrophil membrane remain to be elucidated. Membrane PR3 is unlikely to result from azurophil granule mobilization since CD63, which is a sensitive marker of azurophil granule exocytosis [15], was absent or weakly expressed on freshly isolated PMN independently of the importance of the PR3-positive population. This contrasted with the massive membrane expression of CD63 induced by degranulating stimuli, such as cyt.…”

“…B and FMLP resulted in a marked de novo expression of CD63 on the cell surface, showing that indeed azurophil granules have fused with the plasma membrane [14]. The negative results obtained with anti-GPIIblIIa confirmed that the positive CD63 labelling was not due to activated platelets which strongly express CD63 and may bind neutrophils [15].…”

Targeting factor VIII expression to platelets for hemophilia A gene therapy does not induce an apparent thrombotic risk in mice

“…Activated platelets bind to leukocytes and form PLAs [33,34]. Monitoring of PLAs has been suggested for assessment of thrombosis [35].…”

Apheresis‐induced platelet activation:comparison of three types of cell separators

“…May it even be harmful to transfuse activated platelets? P-selectin (CD62P), shown to be the platelet receptor for WBC binding, 42 was the most prominent activation marker in this study. High platelet surface expression of CD62P has been suggested to result in fast WBC-mediated clearance of transfused platelets from the circulation.…”