Effects of delayed addition of Epo, IL-6/sIL-6R, or SCF + IL-6/sIL-6R on erythroid burst formation by 200 PB-derived CD34⁺IL-6R⁻ cells supported by IL-3 or SCF + IL-3 in serum-containing cultures. (▨) The mean ± SD of the number of BFU-E is shown. Statistical analysis was performed using the two-tailed Student's t-test. NS, not significant.