2.1 Phases of the immune response

This figure has a horizontal time axis running from zero, the time of infection, to 14 days; then there is a break in the axis, beyond which one month and one year are marked, but on a compressed scale. The change in activity of the various immune defences over time is represented by the width of horizontal bars. The time course of infection plot shows that after a brief lag of less than a day, virus number rose to reach a peak at 5 days, and fell to zero by 9 days post-infection. Interferon and natural killer cells were active from the time of infection, peaked within 2 days, and remained at a constant high level throughout the infection period. While interferon activity then declined to zero, the activity of NK cells dropped to a low level, and was still at this level a year after infection. Cytotoxic T cells, helper T cells and B cells all started to become active about 3 days post-infection, they were maximally active at the peak of infection, and their activity declined slowly post-infection to about half their highest levels, by 14 days. Subsequent to this, they remained at a low level as memory cells Production of antibody only began at the time of peak infection (at 5 days), but activity remained high for nearly a month post-infection, declining thereafter.