Metacyclic promastigotes in the upper 10% Ficoll were collected and washed twice with PBS 1× (Gibco /Invitrogen, Paisley, UK). Blood donations were collected from healthy volunteers

(who provided informed consent) at the Blood Transfusion Service of Tunis. Monocyte-derived DCs were generated from peripheral blood mononuclear cells (PBMC), as described previously [22]. Briefly, peripheral blood mononuclear cells (PBMC) were obtained from heparinized venous blood by passage over a Ficoll Hypaque gradient (GE Healthcare Bio-Sciences AB). After 2 h of incubation, Decitabine adherent cell fraction was cultured in complete RPMI-1640 medium containing 2 mmol/l L-glutamine, 100 U/ml penicillin, 100 µg/ml streptomycin and supplemented

with 10% fetal calf serum at 37°C and 5% CO2 for 6 days. Recombinant human granulocyte–macrophage colony-stimulating BVD-523 datasheet factor (GM-CSF) and IL-4 (R&D Systems, Minneapolis, MN, USA) were added to culture on days 0, 2 and 4 at 1000 U/ml and 25 ng/ml, respectively. On culture day 6, DCs were harvested and washed. Viability and cell number were determined by trypan blue exclusion. To study the effect of Lm parasites on DC differentiation, monocytes (CD14+ cell population) were obtained from PBMC by positive selection using magnetic cell sorting (Midi Macs; Miltenyi Biotec, Auburn, CA, USA), resuspended at 5 × 105 cells/ml in complete medium and plated in 24-well tissue-culture plates. Cells were incubated at 37°C in 5% CO2 in the presence or absence of metacyclic promastigotes of the four Lm clones (HV, LV, HVΔlmpdi and LVΔlmpdi) at a parasite/monocyte ratio of 5:1 and without washing to remove free parasites. GM-CSF and IL-4 were added on the same day as the parasites. On days 2 and 4 fresh medium was replaced with GM-CSF and IL-4 without further addition of parasites. Cells were harvested on day 6 and validated as DC using flow cytometry. They were washed, resuspended

at 2·105/tube Exoribonuclease in PBS–1%bovine serum albumin (BSA)–0·1%NaN3 and labelled for 30 min with the appropriate concentration of fluorochrome-conjugated monoclonal antibodies to the following cell antigens: CD1a, CD40, CD86, human leucocyte antigen D-related (HLA-DR), CD14, CD19, CD3 and CD56 (BD Pharmingen, San Jose, CA, USA). After two washes, cells were fixed with PBS–0·3% paraformaldehyde. Appropriate isotype controls were included. Flow cytometry was performed on a FACSVantage machine (Becton Dickinson, Sunnyvale, CA, USA) and data were analysed using CellQuest (Becton-Dickinson, San Jose, CA, USA) and WinMDI (version 2.8) software. DCs were routinely CD1a+, HLA-DR+, CD40+ and CD86+ and negative for CD14, CD3 and CD19.