Activated and unactivated platelet adhesion to monocytes and neutrophils

Abstract

To examine the possible receptor-ligand pairs mediating adhesion of activated and “unactivated” platelets to leukocytes and the kinetics of leukocyte-platelet binding, we developed a flow cytometric assay using isolated cell fractions to accurately measure heterotypic cell adhesion, including both total leukocyte-platelet conjugate formation as well as the number of platelets bound per leukocyte. We have shown that (1) activated platelet binding to both polymorphonuclear leukocytes (PMN) and monocytes is dependent on both a specific epitope (blocked by monoclonal antibody G1) of granule membrane protein-140 (GMP-140) and the presence of divalent cations; (2) unactivated platelets bind to 87% of viable, resting monocytes but to only 34% of PMN; (3) the receptor(s) on unactivated platelets that mediate adhesion to PMN and monocytes do not require divalent cations and become nonfunctional after thrombin activation; and (4) the kinetics of platelet adhesion to monocytes and PMN indicate that monocyte adhesion is favored over neutrophil adhesion. We conclude that platelet- heterotypic cell adhesion is a dynamic process reflecting the activation status of the platelet and differential binding abilities of leukocytes.

Clopidogrel, but not abciximab, reduces platelet leukocyte conjugates and P‐selectin expression in a human ex vivo in vitro model

“…The principal findings of this study were as follows: (1) Clopidogrel significantly reduced CD62 expression and formation of PLA induced by TRAP or ADP. (2) Abciximab administered in vitro to platelets either untreated or pretreated with clopidogrel did not affect expression of CD62 or formation of PLA after stimulation with thrombin receptor signaling. (3) Expression of CD62 and formation of PLA increased when platelets were stimulated with ADP through purinergic receptors, and this enhancement was blunted by pretreatment with clopidogrel.…”

“…Our results were consistent with previous findings that plateletmonocyte aggregates form at a higher rate than are platelet neutrophil aggregates and that TRAP and ADP only marginally increase lymphocyte-platelet binding. 2,20 Intracellular cross-talk and binding of platelets to leukocytes have been investigated in various disease states. Increased PLA formation has been found in unstable coronary artery disease, 10 myocardial infarction, 21 and cardiopulmonary bypass.…”

“…Leukocytes are an additional cellular component of thrombi and are able to adhere to platelets even under high shear stress conditions. 1,2 The adhesion of leukocytes to platelets to platelet-leukocyte aggregates (PLA) deposited at the site of vascular injury therefore may be an important mechanism by which leukocytes contribute to hemostasis and throm-bosis. The pathophysiologic consequences of formation of PLA by means of platelet CD62 binding to its leukocyte ligand P-selectin glycoprotein ligand 1 includes up-regulation of CD11/CD18 on neutrophils, 3,4 secretion of cytokines, 5,6 up-regulation of tissue factor, and increased generation of thrombin by the procoagulant activity of the PLA.…”

Thrombotic thrombocytopenic purpura plasma enhances platelet–leucocyte interaction in vitro

“…In view of the above, and earlier findings that neutrophils specifically interact with PAg (Rinder et al, 1991;Jy et al, 1995), experiments were done in which neutrophils were selectively depleted from WB with immunobeads. Fig 4 shows the effectiveness of neutrophil removal: as seen in the Coulter counter (Model JT3) profiles of WB treated with (a) control HSA beads or (b) anti-CD15 beads, the latter removed >95% of the neutrophils (200-400 fl) with little effect on other leucocytes (50-100 fl).…”

Neutrophil expression of tumour necrosis factor receptors (TNF-R) and of activation markers (CD11b, CD43, CD63) in rheumatoid arthritis

“…CD63 is normally not present on blood PMN [31], while it is highly expressed on activated platelets [32]. Platelets often become activated and bind to PMN during blood collection, This may result in false detection of platelet markers on the neulrophil surface by FACS analysis [33][34][35]. Positive labelling of blood PMN with anti-CD63 MoAb was due to such artefactual platelet binding, as shown by the parallel plateletspecific anti-GPIIla (03) labelling ( Fig.…”