Examples of within-patch dynamics for a single colonization event used for the analytical approximation.

<p>(A) Maximum strength of the CTL response, <i>k</i> = 5 per day. For high levels of viral infectivity <i>β =</i> 9, 10 per day (purple and black lines, respectively), an initial burst of infection is followed by a long-term endemic state. The CTL response is the rate at which CTLs kill infected cells, which is proportional to the number of HIV-specific CTLs in the patch. This increases due to the prevention of egress of HIV-specific CTLs, but even when the maximum rate of CTL killing, <i>k</i>, is reached, this is not sufficient to clear the infected cells from the patch. Even though levels of viral infectivity are high, only a small proportion of cells are infected. For moderate levels of infectivity, <i>β</i> = 5, 6, 7, 8 per day (orange, green, cyan, and blue lines, respectively), an initial burst of infection also occurs, accompanied by an increase in the strength of the CTL response. Eventually, the rate of CTL killing becomes sufficiently high to eliminate the infected cells from the patch, and subsequently the HIV-specific CTLs egress from the patch. For lower levels of infectivity, bursts of infection fail to establish. (B) Maximum strength of the CTL response, <i>k</i> = 1 per day. For moderate and high levels of viral infectivity (<i>β</i> = 5, 6, 7, 8, 9, 10 per day), an endemic state is now reached, and a much higher proportion of cells are infected compared to when <i>k</i> = 5 per day. Equations describing the within-patch dynamics are found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002567#pbio.1002567.s016" target="_blank">S1 Text</a>, and model parameters are as described in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002567#pbio.1002567.t001" target="_blank">Table 1</a>.