IL-6 suppresses cDC1 development from murine and human progenitors. (A) Sort-purified CDPs cultured with Flt3L and IL-6 (0, 1, 5, and 25 ng/ml) for 4 d and analyzed. Shown is FACS analysis of MerTK⁻ B220⁻ SiglecH⁻ cells. Data are representative of four independent experiments. (B) The bar-scatter graphs show average cDC frequencies in the single cell gate (left, gray) and cDC1 (right, red) or cDC2 (right, blue) in total cDCs of the indicated conditions (average % ± SD, n = 4). (C) Analysis of human cDC1 differentiated from umbilical cord blood–derived CD34⁺ progenitors cultured with SCF (20 ng/ml), GM-CSF (20 ng/ml), IL-4 (20 ng/ml), Flt3L (100 ng/ml), and various concentrations of IL-6 (0, 1, and 5 ng/ml) for 14 d. (D) The bar-scatter graphs show average cDC1 frequencies in the single cell gate of the indicated conditions (average % ± SD, n = 3). (E and F) Analysis of cDCs in the (E) spleen and (F) MLNs of Zbtb46^egfp/+ mice injected i.p. with PBS, EL4-empty, or EL4-IL-6 tumor (10⁶ cells) on day 14 after injection. The histogram for the splenic cDCs is representative of two independent experiments. (G and H) Sort-purified OT-I and OT-II (2.5 × 10⁵ cells of each) were transferred i.v. into WT or Irf8 +32^−/− mice inoculated 14 d earlier with PBS, EL4-empty, or EL4-IL-6 tumors. OVA-loaded splenocytes (5 × 10⁵ cells/mouse) were transferred i.v. after 3 h. (G) In vivo proliferation of OT-I (upper panel) and OT-II (lower panel) on day 3 after transfer. (H) Bar-scatter graphs from G for OT-I (upper) and OT-II (lower) of the indicated conditions (average % ± SD). Individual mice are shown as dots. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 (Student’s t test).