CD4+CD25hi T cells were isolated by MACS using the CD4+CD25+ Regulatory T Cell Isolation Kit (Miltenyi Biotec GmBH, Bergisch Gladbach, Germany). According to the protocol recommended by the manufacturer, a two-step isolation was performed, firstly isolating CD4+ cells and secondly enriching for CD25hi T cells using a (suboptimal) concentration of CD25 MicroBeads. CD4+CD25−/low T cells and CD4− cells together were considered as Treg-depleted PBMC. For

the total PBMC populations, the obtained cells were added back (mock depletion). For three donors the depletion was not successful Deforolimus purchase (no decrease in Treg frequency after depletion) and these donors were excluded for analysis of depletion effects. Mean depletion was 62.9%

(range 20.9–100%). To analyze Treg phenotype, PBMC were fixed and permeabilized with a FOXP3 Staining set (eBioscience, San Diego, CA, USA) and stained with fluorochrome labeled check details anti-CD3, anti-CD4, anti-CD25, anti-CTLA-4 (BD Biosciences, Franklin Lakes, NJ, USA), anti-FOXP3 (Miltenyi) and anti-GITR (R&D Systems, Minneapolis, MN, USA) Ab. To monitor proliferation BrdU incorporation was assessed using the BrdU Flow Kit (BD). Total and CD4+CD25hi depleted PBMC were cultured in RPMI 1640 (Gibco, Invitrogen, Carlsbad, CA, USA) supplied with 10% FBS (Greiner Bio-One GmbH, Frickenhausen, Germany) and 10 μM BrdU. BCG (Bio Farma, Bandung, Indonesia, 0.5 μg/mL), 1×106P. falciparum pRBC or 1×106 uninfected Adenosine RBC (uRBC) were used for stimulation. After 96 h cells were fixed in 2% formaldehyde (Sigma-Aldrich, CA, USA) and preserved

at −80°C. After thawing, cells were permeabilized and incubated with DNase (Sigma-Aldrich), labeled with anti-BrdU, anti-CD4 and anti-CD25 Ab (BD), acquired and analyzed. Proliferation of effector T cells was defined as the percentage of BrdU-positive cells within the CD4+CD25+ T-cell population. Cytokine production was assessed using the Multiplex Bead Immunoassay for IFN-γ, IL-5, and IL-13 according to the supplied protocol (Biosource, Invitrogen, Carlsbad, CA, USA). Samples were acquired with Luminex 100™ xMAP technology (Luminex, Austin, TX, USA). Half the detection limit supplied by the manufacturer was used, relevant background values (control medium for BCG, uRBC for pRBC) were subtracted and zero or negative values were set at 1 pg/mL. Statistical analysis was performed in SPSS 14.0. Comparisons of basic phenotypes and responses were tested with Mann–Whitney test for data not normally distributed. For total versus depleted samples paired analysis was done using Wilcoxon Signed Ranks Test. In the multiplex cytokine analysis Bonferroni correction was applied by multiplying the p-values by the number of non-correlated measurements. We acknowledge the technical expertise of Marga van de Vegte-Bolmer in production of P. falciparum culture material.