Blockade of CD4, but not of type I or type II IFN, inhibits AT-2 HIV-induced IDO. (A) IDO mRNA expression was measured in PBMCs from HIV-uninfected donors after exposure to AT-2 HIV in presence or absence of Ab against IFN-α, IFN-β, and/or IFN-γ or CD4; expression was normalized on the AT-2 HIV-treated condition (100%) for each experiment; mean values (n = 3) ± SE are shown. (B) IDO protein was detected by flow cytometry in pDCs (CD4⁺CD123⁺BDCA2⁺) from PBMCs cultured in presence of microvesicles (control; green), AT-2 HIV (red), or AT-2 HIV + anti-CD4 mAb (blue); 1 representative experiment of 3 tested is shown. (C) Ratios between the concentration of kynurenine (μM) and tryptophan (mM) were measured by HPLC in supernatants from PBMCs cultured with AT-2 HIV in presence or absence of Ab against CD4; kyn/Trp ratios were normalized on the AT-2 HIV-treated condition (100%) for each experiment; mean values (n = 3) ± SE are shown.