Franny Jongbloed

159 6 MORBID OBESITY, BARIATRIC SURGERY AND T-CELL AGING (for example by their general practitioner). All blood samples were collected in 10.0 mL BD Lithium-Heparin tubes (Franklin Lakes, NJ, USA), with a maximum of two tubes per time point. CMV serology Cytomegalovirus (CMV) serology was assessed of all participants included in the study at the diagnostic Department of Virology of Erasmus University Medical Center, by determining the presence of plasma IgG antibodies to CMV with an enzyme immune assay (Biomerieux, VIDAS, Lyon, France). The results were expressed as arbitrary units/mL (AU/ mL), and an outcome of ≥ 6 AU/mL was considered positive. T-cell phenotyping and PBMC isolation A whole blood staining was performed and analyzed on the BD FACSCanto II (BD (Erembodegem, Belgium) using FACSDiva software version 6.1.2 (BD) in order to determine percentages and absolute numbers of T-cell subsets (Table 1). The analysis procedure as well as further characterization of the T-cells has been described previously 40 . Peripheral blood mononuclear cells (PBMC) were isolated from heparinized blood samples by Ficoll gradient centrifugation as described in detail before 41 . PBMC were stored at -150 o C at 10x10 6 per vial until further experiments. Table 1. T-cell subsets and their corresponding staining markers T-cell subset Marker Recent thymic emigrants (RTE) CD31+ naive Naive T-cells CD45RO- / CCR7+ Central memory T-cells (CM) CD45RO+ / CCR7+ Effector memory T ceclls (EM) CD45RO+ / CCR7- Terminally differentiated effector memory T-cells (EMRA) Total memory T-cells (MEM) CD45RO - / CCR7- Sum of CM, EM & EMRA Advanced differentiated T-cells CD28null