Assessing the sensitivity of our analysis to the assumption that 2% of naive cells are found in blood. (A) Total body naive population as a function of age. (B) Predicted rate of proliferation. (C) Predicted rate of loss. (D) Predicted absolute number of cells exported by thymus (solid line), produced in periphery (dashed line), and lost from naive pool (gray line, fixed 2% for all ages; dotted line, proportion of cells in the blood increases linearly from 1% at birth to 2% at age 20).