Tα1 expands pDCs from bone marrow precursors and activates tryptophan catabolism. (A) Surface expression of CD11c, CD11b, and B220 on DCs derived from bone marrow of C57BL6, TLR9^–/–, or IFN-αβR^–/– mice and cultured with GM-CSF/IL-4 (GM-DCs) or FLT3L (FL-DCs) in the presence of Tα1(+) or the scrambled peptide (–). Percent of double-positive cells is indicated. In microscopic pictures, cells were stained with Diff-Quik stain (Carlo Erba Reagents, Milan, Italy). Original magnification, × 100 (obtained with a 100×/1.25 oil-immersion objective lens). (B-C) Effect of Tα1 on cytokine production (enzyme-linked immunosorbent assay [ELISA]) by GM-DCs or FL-DCs (B) or purified DC populations from GM-DCs (C) cultured in serum-free medium (1 × 10⁶ cells/mL) with unopsonized Aspergillus conidia (5 × 10⁵/mL) for 24 hours. The IDO inhibitor 1-MT was added at 2 μM. Data are aggregated results from 3 independent experiments. The detection limits (pg/mL) of the assays were less than 16 for IL-12p70 and less than 12 for IL-10. (D) Increased IDO function and expression in DCs derived as in panel A. Cells were assessed for IDO protein expression by immunoblotting and for kynurenine production. Positive and negative controls consisted of IDO protein–expressing MC₂₄ transfectants and mock-transfected MC₂₂ cells, respectively (not shown in the figure). Data are means ± SE of triplicate samples in 1 experiment representative of 3. *P < .05, Tα1-treated versus untreated cells.