Increasing numbers of APC were co-cultured in round-bottom 96-well plates and in complete medium with 105 CFSE-labeled OT-II cells previously enriched by negative selection using a cocktail of PE-labeled mAb, anti-PE microbeads (Miltenyi) and LD columns (Miltenyi). At day 5, CFSE dilution was determined by flow cytometry. A fixed number of Calibrite™ beads (BD) were added

to each sample to quantify the absolute number of OT-II cells per well. Naïve CD4+ T cells, defined as CD25−FR4−CD62LbrightCD44lowCD4+, were purified from CD4-enriched (Dynal® Mouse CD4 PLX3397 chemical structure negative isolation kit, Invitrogen) spleen and total lymph node cells on a MoFlo™ or FACSAria™ (BD) cell sorter. The population was routinely more than 98% pure and free of Foxp3+

cells (not shown). Before transfer, T cells were labeled with 2 μM of CFSE, washed and resuspended in PBS. An amount of 1–2×106 cells were adoptively transferred into CD45.1+ or CD45.2+ congenic B6 mice. One day later, mice were injected i.v. or in the footpad with indicated amount of OVA323–339-coupled mAb alone or in combination with 40 μg this website poly I:C or 100 μg curdlan. CD4+ T-cell responses were assessed 4–6 days after immunization or at the indicated time points. Red-blood-cell-depleted splenocytes were restimulated in complete medium with either 10 μg/mL of OVA323–339 peptide or 10 ng/mL of PMA (Sigma) and 1 μg/mL of ionomycin (Calbiochem). After 30 min, Brefeldin A (Sigma) was added to the culture at a final concentration of 10 μg/mL, and the cells were incubated for three more hours. Alternatively, in some experiments, splenocytes were restimulated for 3 days in complete medium with or without 10 μg/mL of OVA323–339 peptide. Cytokine accumulation in the supernatant was then monitored by ELISA. Flat-bottom 96-wells plates (MaxiSorp™ Nunc-immunoplates) were coated with 2 μg/mL of 7H11 mAb. After overnight CYTH4 incubation, unbound mAb was washed away (PBS, 0.05% Tween 20) and non-specific binding sites were blocked with PBS supplemented with 2.5% FBS and 0.2% NaN3. Serially diluted sera were then plated and incubated for 6 h

at room temperature. After six washes, bound Ab were detected with biotinylated anti-mouse IgG1 (B68-2, BD) or anti-mouse (5.7, BD) mAb or with biotin-SP-conjugated anti-mouse IgG F(ab′)2 (Jackson Immunoresearch). Plates were then washed extensively and incubated with extravidin®-conjugated alkaline phosphatase (Sigma). After six washes, the presence of bound Ab was revealed using p-Nitrophenyl phosphate (Sigma). Wells were considered as positive when the value of the absorbance measured at 405 nm was superior to the one obtained with the serum from a PBS-injected mouse+3x SEM. The Ab titer corresponds to the last dilution scoring positive. This study was funded by Cancer Research UK. C. R. S. acknowledges the support of the Fondation Bettencourt-Schueller.