Fig. 1.

Intravenous immunoglobulin (IVIg) treatment selectively activates circulating regulatory T cells (T_regs), but not conventional T helper cells (T_conv). (a) Percentages of CD3⁺CD4⁺ and CD3⁺CD8⁺ in peripheral blood mononuclear cells (PBMCs) did not alter after IVIg treatment. (b) Density plot shows the gating strategy of T_regs and T_conv after gating on CD4⁺ cells. Histograms show intracellular forkhead box protein 3 (FoxP3) expression in T_regs and surface expression of human leucocyte antigen D-related (HLA-DR) on T_regs and T_conv obtained before, immediately after and at day 7 after IVIg treatment of a representative patient. (c) Baseline percentages of CD25⁺FoxP3⁺ T_regs within circulating CD4⁺ T cells, (d) mean fluorescence intensity (MFI) of FoxP3 in T_regs and (e) percentages of T_regs expressing HLA-DR from healthy blood donors (n = 10) and patients treated with low-dose IVIg (n = 12) or high-dose IVIg (n = 15). (f) Percentages of CD25⁺FoxP3⁺ T_regs within the CD4⁺ population before, immediately after and 7 days after IVIg treatment in patients who received low-dose (n = 12) or high-dose IVIg (n = 15). (g) MFI of FoxP3 in T_regs, (h) percentages of T_regs and (i) percentages of T_conv expressing HLA-DR before, immediately after and 7 days after IVIg treatment in patients who received low-dose (n = 12) or high-dose IVIg treatment (n = 15). Horizontal lines represent median. *P < 0·05.