*IFNγ but not IL-2. The IFNγ shifts the balance of the immune response in favour of TH<sub>1</sub> cells and there is therefore an increased level of T-cell proliferation. The initiation of the immune response via CTL leads to the selective proliferation of CTL which enhances the main mechanism of killing virally-infected cells. | *IFNγ but not IL-2. The IFNγ shifts the balance of the immune response in favour of TH<sub>1</sub> cells and there is therefore an increased level of T-cell proliferation. The initiation of the immune response via CTL leads to the selective proliferation of CTL which enhances the main mechanism of killing virally-infected cells. |