IVIg-mediated protection against EAE depends on the presence of Treg. (A) IVIg failed to protect mice that were depleted of Treg. Mice n = 7 in each group. For Treg depletion, animals received 100 μg of antibody PC61 intraperitoneally 10 days before EAE induction (squares). The control groups were not depleted (circles). The mice were treated (open symbols) or not (solid symbols) with IVIg. All mice were immunized with MOG_35-55. Clinical EAE was assessed as mentioned previously. (B) Reappearance of Treg in the blood of depleted mice, after EAE induction. Mice were depleted of T cells and immunized with MOG_35-55 in the presence (□) or absence of IVIg (■). They were bled at intervals of 7 days after immunization (n = 5 for each group). Two control groups of naive untreated animals, which were Treg depleted (░) or not () were included. The percentage of cells coexpressing CD25 and Foxp3 in the CD4 population (Treg) was assessed in the blood using flow cytometry, and the mean percentages (± SD) for 5 mice in each group are represented. Similar results were obtained in 2 independent experiments. Data are the mean plus or minus SD.