DC are more efficient stimulators of naive Th cells than Mφ or freshly isolated monocytes. Different number of stimulator cells (stim.) all obtained from the same donor were cocultured with allogenic naive Th cells. The proliferative response was determined at day 6. The results are presented as mean counts per minute ± standard error of the mean (SEM) of triplicate cultures. Results are representative of three independent experiments.