2/8H5 (Enzo Life Sciences (UK) Ltd, Exeter, UK; Mouse clone: 9H10, eBioscience). IgG isotype control antibodies were from Abcam plc, Cambridge, UK, or eBioscience. The selective ELISA for human sCTLA-4 used the anti-CTLA-4 murine mAb clone

BNI3 (2 μg/mL) as the capture reagent and biotinylated JMW-3B3 as the sCTLA-4–specific detection reagent using the same protocol described for the cytokine ELISA mentioned above. Measurement of murine sCTLA-4 by ELISA was conducted according to the same procedures as for human sCTLA-4, but with a hamster anti-mouse CTLA-4 capture Ab (clone: 9H10). Affinity purified sCTLA-4 was used to construct standard curves. Specific primers for sCTLA-4 mRNA were used to amplify a fragment of 93 bp. The reaction consisted R428 molecular weight of 3 μL cDNA, 1.5 μL of each primer (0.5 μM), 1 μL of the corresponding probe (0.2 μM), 10 μL of LightCycler 480 probes master (Roche), and distilled water up to a final volume of 20 μL. The sCTLA-4–specific primer and probe sequences were as follows: sCTLA-4F: 5′-CAT CTG CAA GGT GGA GCT CAT-3′ and sCTLA-4R: 5′-GGC TTC TTT TCT TTA GCA ATT ACA TAA ATC-3′; Rapamycin in vivo probe: 5′-ACC GCC ATA CTA CCT GGG CAT AGG CA -3′, labeled with FAM. Amplification was performed in a LightCycler 2.0 instrument (Roche Diagnostics Ltd, Burgess Hill, UK). A reference to the standard curve was included in each run, and all

samples were replicated once. Data from cells stimulated in vitro for 5 days at 37°C 5% CO2 with PPD, SEB, or anti-CD3 mAb were compared against nonstimulated

resting cell–derived mRNA. Human B7.1Ig or B7.2Ig (2 μg/mL, Axxora, Nottingham, UK) was bound to protein A magnetic beads and incubated with a sCTLA-4 positive serum in the presence of an isotype Ab control, pan-specific anti-CTLA-4 mAb, or JMW-3B3 mAb (all 5 μg/mL). Bound sCTLA-4 was then eluted with Glycine HCl (pH 3.2) and detected in a conventional anti-CTLA-4 ELISA. Analyses of Treg-cell Myosin lines or fractionated T-cell subsets were conducted by incubating cells for 4 h in the presence of Brefeldin A (Golgiplug, BD Biosciences), before staining for extracellular CD4 (FITC), CD25 (PE-Cy™7), and CD127 (Alexa Fluor®647) using a regulatory T-cell cocktail kit (BD Biosciences). Cells were subsequently fixed and permeabilized (BD Cytofix/Cytoperm fixation/permeabilization solution kit, BD Biosciences) before staining for intracellular FoxP3 (V450, BD Biosciences) and sCTLA-4 (clone: JMW-3B3, PE). Flow cytometry was performed with an LSR II flow cytometer (BD Biosciences) and data analyzed with FCS Express 3 software. Isotype controls were used to exclude nonspecific staining and to set gates. CD4+CD25+ and CD4+CD25− T cells were prepared using a Dynabeads® Regulatory CD4+CD25+ T-cell kit (Invitrogen) according to manufacturer’s instructions. Purity of fractionated cell populations was checked using flow cytometry.