Quantification of entry into and exit from the cell cycle in human lymphocyte cultures

A mathematical model is presented for the analysis of transition between cycling and non-cycling compartments by cells responding to a growth stimulus. The cellular age distribution as a function of time is derived from sequential [3H]thymidine pulse labeling indices. Rates of entry into and exit from the cycling compartment are determined on the basis of labeling indices obtained after instantaneous and long duration [3H]thymidine pulses. Analysis of an experiment involving sequential measurements over the whole lifespan of a human lymphocyte culture stimulated by phytohemagglutinin is presented as an example of the application of this method.