Identification of a CD34⁺CD41^low population. (A) CD34 expression and % of CD41⁺ cells at day 10. CD34⁺ cells were cultured as in Figure 1A, and analyses were performed on day 10. (B) (Left) Expression of CD34 and CD41 markers at day 10 in control culture conditions. Representative flow density plot identifies 2 subpopulations based on CD41 expression, CD34⁻CD41⁺ and CD34⁺CD41^low. Gate G1 was later used in cell sorting experiments (Figure 3). (Right) Level of CD41 expression at day 10. The level of expression of CD41 in the CD34⁺CD41⁺ quadrant as measured by FL2 fluorescence intensity was adjusted at 100% (gray bar). In CD34⁻CD41⁺ (black bar), CD41 expression was increased by 1.7 ± 0.1-fold (mean ± SEM in 8 experiments; paired Student t test, **P < .01), defining a CD34⁻CD41⁺ population by comparison with the CD34⁺CD41⁺ population defining CD34⁺CD41^low cells. (C) (Left) Expression of CD34 and CD41 markers at day 10 in MSC-treated cultures. (Right) Level of CD41 expression at day 10.