In vitro and rescue potentials of L-selectin subsets. (A) L-selectin^Neg (○) and L-selectin^Pos (▪) fractions were collected and cultured in methylcellulose as described in “Materials and methods.” Colonies visible with the aid of a dissecting microscope were counted at the indicated days of culture and plotted as a percent of total cells plated. Each symbol represent the average of 4 to 8 methylcellulose plates counted over 3 replicate experiments. Error bars represent SEM. (B) Colonies formed by L-selectin^Neg (○) and L-selectin^Pos (▪) fractions were collected, stained with PI, and analyzed by flow cytometry. Each symbol represents the average number of viable cells (PI^Neg) per colony analyzed at the times indicated. Eight to 24 colonies were analyzed for each data point. Data were pooled from 3 replicate experiments and error bars represent SEM. (C) Viable colonies collected for analysis in panel B were evaluated for Ly-6G and CD19 expression. Bars represent the number of colonies containing equal to or more than 30 PI^Neg cells that expressed either or both (multilineage) of these markers. A total of 144 colonies from L-selectin^Pos progenitors and 128 from L-selectin^Neg progenitors were analyzed for panels B and C. (D) Lethally irradiated (13 Gy) mice were given transplants intravenously with 10³ Thy-1.1^Neg c-kit^Hi L-selectin^Neg (▵) or Thy-1.1^Lo c-kit^Hi L-selectin^Pos (•) progenitors, or 10³ Thy-1.1^Lo c-kit^Hi hematopoietic stem/progenitor cells (⋄), or did not receive transplants (▪).