An inappropriate and persistent immune activation has been suggested to contribute to long-term mortality and morbidity after
heart transplantation. Several lines of evidence suggest that platelets do not only promote
thrombus formation, but also act as inflammatory cells. In the present study, we investigated if long-time survivors of
heart transplantation (mean time since
transplantation 6.5 yr) were characterized by enhanced platelet activation as assessed by different experimental approaches. Our main findings when comparing heart transplant recipients (n = 52) and age- and sex-matched healthy controls (n = 38) were: (i) platelets from heart transplant recipients showed enhanced expression of both
P-selectin and CD63 as assessed by flow cytometry; (ii) platelets from these patients also contained significantly increased levels of soluble
CD40 ligand and tended to release higher levels of this
cytokine upon
SFLLRN stimulation as assessed by
enzyme immunoassay; (iii) heart transplant recipients had increased levels of soluble
P-selectin in platelet-free plasma; and (iv) the enhanced platelet activation after
heart transplantation was most pronounced in those with concomitant
hypertension. These findings suggest that long-term survivors of
heart transplantation are characterized by enhanced activation of platelets, possibly contributing to the persistent immune activation and clinical complications in these patients.