Distribution of cells according to their CFSE fluorescence after being cultured.

Distribution is shown after 3 days of incubation in serum-free culture with (B) or without (A) exogenous growth factors (as shown) in addition to an initial period of overnight culture prior to selection of a LD CFSE⁺ population. Open peaks show the data for control (undivided) cells incubated under the same conditions but in the presence of colcemid to block cell division. The presence of FL, SF, and H-IL-6 stimulated the cells in this experiment to complete an extra 4 cycles (7 divisions shown in B versus 3 divisions in A).