Abstract
Recent work has revealed an essential involvement of soluble CD40L (sCD40L) in inflammation and vascular disease. Activated platelets are the major source of sCD40L, which has been implicated in platelet and leukocyte activation, although its exact functional impact on leukocyte-platelet interactions and the underlying mechanisms remain undefined. We aimed to determine the impact and the mechanisms of sCD40L on neutrophils. We studied neutrophil interactions with activated, surface-adherent platelets as a model for leukocyte recruitment to the sites of injury. Our data show that CD40L contributes to neutrophil firm adhesion to and transmigration across activated surface-adherent platelets, possibly through two potential mechanisms. One involves the direct interaction of ligand-receptor (CD40L-CD40), i.e., platelet surface CD40L interaction with neutrophil CD40; another involves an indirect mechanism, i.e. soluble CD40L stimulates activation of the leukocyte-specific β2 integrin Mac-1 in neutrophils and thereby further promotes neutrophil adhesion and migration. Activation of the integrin Mac-1 is known to be critical for mediating neutrophil adhesion and migration. sCD40L activated Mac-1 in neutrophils and enhanced neutrophil-platelet interactions in wild-type neutrophils, but failed to elicit such responses in CD40-deficient neutrophils. Furthermore, our data show that the protein kinase C zeta (PKCζ) is critically required for sCD40L-induced Mac-1 activation and neutrophil adhesive function. sCD40L strongly stimulated the focal clustering of Mac-1 (CD11b) and the colocalization of Mac-1 with PKCζ in wild-type neutrophils, but had minimal effect in CD40-deficient neutrophils. Blocking PKCζ completely inhibited sCD40L-induced neutrophil firm adhesion. Moreover, sCD40L strongly stimulates neutrophil oxidative burst via CD40-dependent activation of PI3K/NF-KB, but independent of Mac-1 and PKCζ. These findings may contribute to a better understanding of the underlying mechanisms by which sCD40L/CD40 pathway contributes to inflammation and vascular diseases.
Highlights
Platelet activation and leukocyte-platelet interactions play an important role in the pathogenesis of vascular disease including atherosclerosis and restenosis [1,2,3]
The wells were pre-coated with fibrinogen alone or with fibrinogen to which platelets were bound and activated and fixed with 2%PFA to prevent CD40L shedding from activated platelets
One important pair involves the interaction of P-selectin expressed on the activated platelet surface with P-selectin glycoprotein ligand1 (PSGL-1), its counter receptor, expressed on leukocytes [18,34]
Summary
Platelet activation and leukocyte-platelet interactions play an important role in the pathogenesis of vascular disease including atherosclerosis and restenosis [1,2,3]. Experimental studies have demonstrated that after arterial denudation injury platelet deposition precedes leukocyte accumulation at sites of injury, and early recruitment of leukocytes to the sites of injury is likely mediated through leukocyte-platelet adhesive interactions followed by leukocyte transmigration through the surface-adherent platelet monolayer, resulting in leukocyte infiltration into vessel wall [4,5]. It is proposed that platelets deposited at injured vessel wall form an adhesive surface that promotes leukocyte recruitment through direct interaction of ligand-receptor pairs between platelets and leukocytes, the mechanism of the interaction has not been completely clarified [2].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
