Dependence on continued presence of Notch ligand.

Number of cells (A) and antigen expression (B) were determined after Lin⁻Sca-1⁺c-kit⁺ cells incubated for 28 days with 4GF, IL-7, and I-Delta1^ext-IgGwere transferred to new cultures and incubated with the same cytokines with (●) or without (▪) I-Delta^ext-IgG. Antigen expression was determined 7 days after transferring to new cultures. Fewer than 0.5% of cells stained with either or both isotype control antibodies. Those without Delta^ext-IgG are shown.