IL-21R is expressed by human pDCs and is functional. (A) Expression of IL-21 receptor was measured by RT-PCR on RNA extracted from human-sorted pDCs from thymus (2 donors) and compared with peripheral blood human T cells (sorted or MACS-enriched for CD3) and human B cells (sorted or MACS-enriched for CD19). Actin amplification was done as a loading control. (B) Total human peripheral blood mononuclear cells were analyzed for expression of IL-21R by flow cytometry. IL-21R surface expression levels on pDCs, T cells (CD4⁺ MACS), B cells (CD19⁺ MACS), and other cells (other) are shown (black lines). Isotype control stainings are shown as gray-filled histograms. IL-21R expression on total B cells is shown as positive control. (C) Flow cytometric analysis of phosphorylated (p) STAT-3 protein in primary pDCs from peripheral blood, thymus, and tonsils stimulated in the presence (black lines) or absence (gray-filled histograms) of IL-21 (25 ng/mL) for 20 minutes. One representative experiment out of 3 is depicted. RCN, relative cell number.