A sample of 5 × 105 cells of PBMC was resuspended in PBS with 1% FCS. PBMC were incubated with saturating concentrations of anti-IL-10R1 mAb (IgG1; R&D systems, Minneapolis, MN, USA) or with isotype-matched control mAb (Immunotech), followed by incubation with FITC-conjugated goat anti-mouse IgG1 polyclonal antibody (Santa Cruz Biotechnologies, Santa Cruz, CA, USA). Cells were then incubated with phycoerythrin-conjugated anti-CD4 mAb (Becton Dickinson). Cells were washed well with 1% FCS/PBS between incubations. Analysis was performed on a FACScan flow cytometer (Becton Dickinson).