Cytokine production by HTLV-1–activated pDCs. IFN-α production by 106 PBMCs (A) and 105 purified pDCs (B) from healthy blood donors cultured alone in the presence of supernatants from HTLV-1 virus producing T-cell line (MT-2) or with influenza virus (Flu) as positive control. (C) Overnight IFN-α production by pDCs were assessed by the use of purified HTLV-1 virions (purified HTLV) from ultracentrifuged MT-2 supernatants (MT-2 SN). (D) IFN-α production by PBMCs in response to various HTLV-1 (p19-equivalent) concentrations (0-500 ng/mL). (E) Kinetic secretion of IFN-α by HTLV-1–stimulated pDCs (300 ng/mL of p19-equivalent) compared with unstimulated pDCs. HTLV-1 capacity to turn pDC into IFN-α (F) and TNF-α (G) producing pDCs was inhibited by sera containing blocking HTLV-1 antibodies from HTLV patients (Serum 1, Serum 2) or by blocking HTLV-1 envelope (gp46) antibody (10 μg/mL) but not using irrelevant antibody (10 μg/mL) or uninfected healthy donor serum (HD serum). Data shown are representative of at least 4 independent experiments. **P < .01; ***P < .001.
