Decreased platelet serotonin levels are associated with platelet activation.

<p>A) Serotonin levels were analyzed in EDTA plasma samples and compared between healthy volunteers (HV) and SLE patients. B) To adjust for differences in total serotonin levels, the relative amount of peripheral versus total serotonin was calculated and compared between HV and SLE patients. SLE patients with a high relative amount of peripheral serotonin (high) was compared to SLE patients with low relative amount of peripheral serotonin levels (low) with regard to C) platelet intracellular serotonin levels, D) serum levels of serotonin, E) platelet microparticle (PMP) count in plasma and F) platelet activation assessed by platelet C4d deposition analyzed by flow cytometry.