Analysis of the processing pathways of exogenous HIV-1 antigens in DCs and in DC-SIGN⁺ cells. (A) HIV-1 exogenous presentation is proteasome-dependent. Primary immature DCs were pretreated with AZT and exposed to the indicated viruses, and an IFNγ Elispot assay was performed using anti-Gag EM71-1 as effectors. The proteasome inhibitor epoxomycin (0.1 μM) or the inhibitor of vesicular acidification bafilomycin-A1 (250 nM) was added 30 minutes before viral exposure. Gag SL9 peptide was used at 10 nM. Similar results were observed with 3 different donors, irrespective of the magnitude of the inhibition by anti–DC-SIGN mAbs (not shown). (B) HIV-1 exogenous presentation in DC-SIGN⁺ cells requires TAP transporters. T2, T3, and their DC-SIGN⁺ counterparts (T2-DCS and T3-DCS, respectively) were exposed to HIV_MN-AT2, and an IFNγ Elispot assay was performed using anti-Pol EM71-1 as effectors. T2 cells are deficient for TAP1 and TAP2 antigen transporters. T3 cells were derived from T2 cells and re-express TAP1 and TAP2 proteins. IV9 peptide was used at 1 nM. Similar results were obtained with EM71-1 effectors (not shown). Data are mean ± SD of triplicates and are representative of 3 independent experiments.