Activation of leukocytes in whole blood samples by N-formyl-methionyl-leucyl-phenylalanine (FMLP) enhances platelet aggregability but not platelet P-selectin exposure and adhesion to leukocytes

Abstract

Adhesion of platelets to neutrophils and monocytes is believed to play an important role in intercellular communication. Evidence has been provided that such heterotypic cell-cell contacts via adhesion molecules may be directly involved in intercellular signal transduction as well as facilitate the action of soluble signal transmitters, e.g. cathepsin G, PAF or nitric oxide. With respect to platelet activation, stimulatory and inhibitory effects of leukocytes have been reported, and the results obtained seem to be influenced by the experimental conditions. We investigated the effect of leukocyte stimulation on platelet behaviour in samples of human citrated whole blood. Adding the chemotactic peptide FM LP, which stimulates neutrophils and monocytes but not lymphocytes and platelets, to stirred whole blood samples resulted in a significant enhancement ( P < 0.01) of spontaneous as well as ADP-induced platelet aggregation (25 vs 33% and 66 vs 69% , respectively). In contrast stirring-induced as well as ADP-induced increase of P-selectin exposure (33 and 107% , respectively) was not affected by FMLP. In unstirred whole blood samples, about 10 to 20% of neutrophils and monocytes had bound platelets to their surfaces, and the number of these heterotypic conjugates was enhanced about twofold during spontaneous platelet aggregation. Addition of FMLP significantly reduced the stirring-induced formation of platelet-neutrophil conjugates but not of platelet-monocyte conjugates. These results indicate that neutrophil and/or monocyte activation in whole blood may enhance platelet aggregation, but not secretion (CD62P exposure) and formation of heterotypic platelet-leukocyte conjugates.

Platelet activation parameters and platelet-leucocyte-conjugate formation in glioblastoma multiforme patients

“…Nevertheless, most studies addressing platelet activation present data of n = 20 or even below. [ 20 , 21 , 23 , 26 , 28 , 35 , 36 , 77 – 84 ]…”

Platelet activation and platelet–leukocyte interaction in dogs naturally infected with Babesia rossi

“…Although platelet P-selectin expression is considered the 'gold standard' marker of platelet activation, circulating activated platelets have been reported to rapidly lose their surface P-selectin expression (Michelson et al, 2001;Moritz et al, 2003). In contrast, activated platelets quickly form circulating aggregates with monocytes and neutrophils of which the circulating half-lives (specifically that of platelet-monocyte aggregates) are significantly longer (Rinder et al, 1991;Losche et al, 1998;Michelson et al, 2001).…”

“…However, the formation of PLA is reported to better reflect the presence of activated platelets (Losche et al, 1998;Russwurm et al, 2002;Wills et al, 2006). Platelet P-selectin expression promotes the interaction between platelets and cells expressing P-selectin glycoprotein ligand-1 (PSGL-1), primarily neutrophils, monocytes, endothelial cells and other platelets (Zeller et al, 2005;Semple et al, 2011;Ghasemzadeh and Hosseini, 2013;Jenne et al, 2013).…”

“…Platelet activation, even in the absence of any detectable blood vessel damage, plays an important role in inflammation and immune regulation (Semple et al, 2011;Jenne et al, 2013). Activated platelets express various bioactive mediators and adhesive proteins that facilitate platelet-to-platelet aggregation, as well as formation of platelet-leukocyte aggregates (PLAs) (Losche et al, 1998;Tarnow et al, 2008;Semple et al, 2011).…”

“…In addition, the interaction of platelet P-selectin and leukocyte PSGL-1 results in neutrophil and monocyte activation, with upregulation of their pro-inflammatory functions. Platelets are therefore considered to be important mediators for cellular communication during inflammatory responses (Losche et al, 1998;Russwurm et al, 2002;Semple et al, 2011;Ghasemzadeh and Hosseini, 2013).…”