Reserpine-sensitive SP cells contain a low proportion of committed cells. All values are expressed as a mean of 5 separate experiments. Expression of mature cell markers is displayed as percentage of SP. The SP contains a low proportion of lymphoid cells (CD2, 4, 5, 8, B220, and NK1.1) and a slightly higher proportion of mature myeloid cells (GR-1⁺ and CD11b^high).