This study was approved by the Oxfordshire Research Ethics Committee (COREC reference 06/Q1605/55). A total of 432 volunteers of European ancestry were recruited in the Oxfordshire area after written informed consent. The cohort consisted of 194 males and 238 females with a median age of 30 years (mean, 33 years; interquartile range, 19 to 56 years). Whole blood was collected into anticoagulant EDTA-containing blood collection tubes (Vacutainer System, Becton Dickinson). PBMCs, purified using Ficoll-Paque density gradients from 50 ml of whole blood, were washed three times in Hanks’ balanced salt solution without Ca2+ and Mg2+ (Invitrogen), and the number of cells was determined using a hemocytometer.
