PTX3 interferes with the cross-presentation of HCV-NS3 epitopes to HCV-specific CD8⁺ T cells upon processing of apoptotic cells. DCs that phagocytosed and processed HLA-A2^- apoptotic cells expressing the HCV-NS3 protein, but not DCs that phagocytosed control apoptotic cells, induced a brisk increase of IFN-γ production by NS3_1241-1260-specific, HLA-A2-restricted CD8⁺ T-cell clone, as evaluated by flow cytometry. This effect abated in the presence of exogenous PTX3 (50 μM). x-axis: forward scatter, FSC-H. Dot plots are gated on CD8⁺ cells and IFN-γ staining. Results are expressed as percentage of cells, as indicated in the top right quadrant. Results of 1 of 3 different experiments are shown (A). AU indicates arbitrary unit. Bars represent the fraction of antigen-specific CD8⁺ T cells expressing IFN-γ when challenged with DCs that had been pulsed with either HLA-A2^- apoptotic cells expressing the NS3 antigen or the relevant NS3_1241-1260 peptide in the presence or in the absence of PTX3 (B). In contrast, no difference in the percentage of IFN-γ-positive cells (y-axis) was detectable when DCs presented the recombinant HCV-NS3 antigen (x-axis; μg/mL) in the absence (○) or in the presence (▪) of PTX3 (50 μM; C). ^*Statistically different from control.