Alpha-defensins NHP-1 and NHP-2 induce strong platelet-activation leading to CD40L expression

Abstract

Rationale Alpha defensins, key players in the innate immune system, accumulate in airway secretions of patients with various chronic inflammatory lung disorders. Activated platelets secret a wide range of biologically active substances capable of inducing or augmenting airway inflammatory responses. The interaction between alpha-defensins and platelets was examined. Methods Activation of platelets by NHP-1 or NHP-2 was assessed by flowcytometry. We analyzed among other things, CD62 expression as a marker of alpha-granule secretion, CD63 expression as a marker of dense body secretion, and binding of fibrinogen, thrombospondin-1 and several coagulation factors to the platelet surface. In addition platelet surface expression of CD40L, a protein belonging to the TNF family, that stimulates dendritic cells, B cells and endothelium cells, was measured and soluble CD40L was quantified by Elisa. Results The used alpha defensins induced strong platelet activation in a dose and time dependent manner. 10μM of NHP-1 or NHP-2 induced platelet stimulation comparable to 1U/ml of the strong agonist thrombin. Platelets bound fibrinogen and thrombospondin-1, secreted the contents of their granules, bound coagulation factors and even built microparticles. NHP-1 and NHP-2 induced CD40L expression on the platelet surface and soluble CD40L was found in the platelet supernatant when platelets were activated. Conclusions Platelets are underappreciated for their contributions to host defense and inflammatory processes. This is the first description that peptides of the innate immune system activate platelets. This new discovered mechanism might be at least in part, responsible for the formation of thrombi in connection with inflammatory processes.