Commitment and proliferation kinetics of human lymphocytes stimulated in vitro: effects of alpha-MM addition and suboptimal dose on concanavalin A response.

We have examined the effect of alpha-methylmannoside (alpha-MM) addition to concanavalin A (con A)-stimulated peripheral human lymphocytes. With a previously established kinetic model, we have, from the time course of proliferation, extracted the responding clone size, rate of entry of this clone into S phase and the length of the lag period. We have studied the effect of con A dose and time of addition of alpha-MM to optimally stimulated cells on these kinetic parameters. We show that neither a low dose of con A nor an early addition of alpha-MM to optimally stimulated cells results in a change in the responding clone size. This is, all of the potentially cells appears to become "committed" to enter the cell cycle regardless of the presence of alpha-MM early in the culture or in the presence of suboptimal stimulation. However, the rate at which these committed cells enter the first S phase is a function of the dose of con A and time of addition of alpha-MM and varies over a wide range. It is the variation in this parameter that accounts for virtually all of the diminished response previously interpreted as a time-dependent irreversible commitment of mitogen-stimulated cells. The previous work using only fixed time points for measuring thymidine uptake and the concept of commitment must be reevaluated in light of the kinetic evidence presented.