Sample Collection. Handling of blood samples was approved by the Research Ethics Committee of the National Institute for Health Development of Estonia (Decision No. 1284), and written informed consent was obtained from healthy volunteers. Blood samples were collected by health professional in a clinical setting. Blood was collected in lithium-heparin containing vacutainer tubes. Two different blood sample collection and transport procedures were used. In the first case, the blood samples were transported to the analysis laboratory on ice packs. Red blood cells (RBC) and plasma were separated by centrifuging the whole blood at 4 ⁰C for 10 min at 1500 rcf. The buffy coat (leukocytes and thrombocytes) was discarded. In the second case, the blood samples were immediately placed in an ice bath after collection for rapid cooling prior to and during transport to the analysis laboratory. The ice-bath cooled blood was centrifuged at 0 ⁰C for 10 min at 400 rcf, to separate the RBC and plasma. The buffy coat was discarded. The plasma fraction was centrifuged a second time at 0 ⁰C for 5 min at 2300 rcf to fully pellet the red blood cells. Blood fractions were either extracted immediately or flash frozen in liquid N2 and stored at -80 ⁰C until extraction.