DC-SIGN promotes MHC-I–restricted HIV-1 exogenous presentation. (A) C1RA2 (▪) and C1RA2-DCS (□) cells were used as stimulator cells in an IFNγ Elispot assay. The effector was the CD8⁺ CTL line EM71-1, which recognizes an HLA-A2–restricted epitope (SL9) from the Gag p17 protein. Stimulating cells were exposed to the indicated viruses and incubated with EM71-1 cells. Activity of EM71-1 cells is depicted as the number of IFN-γ–positive cells for the indicated number of effectors. As a positive control, stimulating cells were pulsed with the cognate peptide (SL9, 0.05 nM). Viral inoculum was 300 ng of p24/10⁶ cells. HIV(VSV) is an env-deleted HIV-1 vector pseudotyped with the VSV-G envelope. HIV_MN-AT2 are aldrithiol 2–inactivated virions (X4 strain MN). (B) T3 (▪) and T3-DCS (□) cells were used as stimulator cells in an IFNγ Elispot assay, as described in panel A. There were 2 effectors used, EM71-1 (left panel) and EM23 (right panel), of which the latter recognizes an HLA-A2–restricted epitope (IV9) from the Pol RT protein. SL9 and IV9 peptides were used at 1 nM. Data are mean ± SD of triplicates and are representative of 3 independent experiments.