Quantification of cell turnover kinetics using 5-bromo-2 '-deoxyuridine

5-Bromo-2'-deoxyuridine (BrdU) is frequently used to measure the turnover o f cell populations in vivo. However, due to a lack of detailed mathematical models that describe the uptake and loss of BrdU in dividing cell populati ons, assessments of cell turnover kinetics have been largely qualitative ra ther than quantitative. In this study, we develop a mathematical framework for the analysis of BrdU-labeling experiments. We derive analytical express ions for the fraction of labeled cells within cell populations that are gro wing, declining, or at equilibrium. Fitting the analytical functions to dat a allows us to quantify the rates of cell proliferation and cell loss, as w ell as the rate of cell input from a source. We illustrate this far the Brd U labeling of T lymphocytes of uninfected and SIV-infected rhesus macaques.