Scaling of naive T-cell densities with age. (A) Estimated mean naive CD4⁺ T cells per kilogram of body mass as a function of age (black line), with 2.5 and 97.5 percentiles at the population level (gray lines). (B) Estimated dependence of mean naive CD4⁺ T-cell density (cells/kg) on log₁₀ body mass.