Predicted post-thymic cell age distributions, for different host ages, using the adaptation model.

<p>The normalised age distributions of naive CD4 and CD8 T cells were generated using parameters obtained from fits to the data from den Braber et al. [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2003949#pbio.2003949.ref008" target="_blank">8</a>] (upper panels) and from the busulfan chimeras (lower panels). Different coloured curves denote different host ages. Distributions illustrate the preferential accumulation with longer-lived and/or more proliferative cell populations with host age. The discontinuity in the gradients at older cell ages derives from uncertainty in the precise form of the age distribution of cells at the beginning of the experiment. We proposed various forms for this distribution, and the parameters of each were estimated from the data. However, for all distributions we explored, the same U-shaped trend emerges over time.