FIGURE 2. Schematic representation of memory response to homologous HCV re-challenge, and outcome of a third challenge following CD4⁺ T-cell depletion.

Following initial rechallenge, the onset of viraemia (red line) is associated with relatively rapid onset of strong CD4⁺ and CD8⁺ memory T-cell responses (black and green lines, respectively). The level of viraemia is lower than in primary infection, and viral clearance is more rapid. Associated transaminase rises (blue line) are also reduced. Following CD4⁺ T-cell depletion (indicated by a red arrow), viral rechallenge is associated with a weaker CD8⁺ T-cell response, which partly controls viraemia but is followed by viral rebound and persistence as escape mutations emerge in MHC class-I-restricted epitopes.