IL-27 and SCF most strongly expand only LSK cells among various kinds of BM progenitors and differentiate them into myeloid progenitors retaining the LSK phenotype.

(A) Expansion of only the c-Kit⁺CD11b⁻Lin⁻ population by IL-27 and SCF in BM cells. Total BM cells were divided into two populations positive or negative for Lin markers, and the Lin⁻ population was further divided into four populations positive for either c-Kit or CD11b, both positive, or both negative. Each population (5 × 10³) purified by sorting was stimulated by either IL-27 or SCF alone, or both, in a round 96-well plate and photographed 2 weeks later. (B-E) Expansion of only the LSK cell population by IL-27 and SCF among various BM progenitors. BM progenitors (4–5 × 10³) purified by sorting were stimulated with IL-27 and SCF. Cell expansion was photographed at indicated periods (B) and cell number of the expanded LSK cell population retaining the LSK phenotype was counted at 1 week (C). Time kinetic analysis of cell numbers in the LSK population retaining the LSK phenotype (D). Representative flow cytometry dot plot analysis of c-Kit and Lin (upper) and of c-Kit and Sca-1 in the Lin⁻c-Kit⁺ population (lower) of expanded LSK cells and progenitor cells at 1 week (E). (F) Expansion of LSK populations in vivo by IL-27 in IL-27 Tg mice. LSK cells were purified by sorting from BM cells of GFP Tg mice and transferred into non-lethally irradiated WT and IL-27 Tg mice. Twenty days later, BM and spleen in these recipient mice were analyzed for GFP⁺ LSK populations. Data are shown as mean ± SEM (n = 2–3) and are representative of at least two independent experiments. *P < 0.05. (G-H) Augmented and prolonged expansion of the LSK cell population by only IL-27 and SCF in vitro. LSK cells (1 × 10³) from WT mice were stimulated by various cytokines together with SCF for 1 to 4 weeks, the stimulated cells were analyzed by flow cytometry (G), and cell number was counted with time course (H). Data are representative of at least two independent experiments.