IL-20 specifically increases numbers and cell-cycling status of mouse multipotential progenitors in vitro and in vivo. (A) IL-20 increases mouse CFU-GEMM but not CFU-GM or BFU-E in vitro. Bone marrow cells (5 × 10⁴) from BDF-1 or C3H/HeJ mice were cultured in methycellulose medium with hemin, 1 U/mL EPO, and 50 ng/mL SCF with or without IL-20. 5% vol/vol pokeweed mitogen mouse spleen cell-conditioned medium (PWMSCM) was added to some cultures. Values represent mean ± SD of 3 triplicates. *P < .05 compared with respective controls without IL-20. (B) IL-20 TG mice had significant increases in numbers and cycling rates of CFU-GEMM, but not BFU-E or CFU-GM, in bone marrow and spleens. Data show the results (mean ± SD) of 19 to 20 animals/group. Each mouse was evaluated separately. Left panels show absolute numbers of myeloid progenitor cells per femur or spleen. Right panels show percentage of myeloid progenitor cells in S-phase. *P < .03 compared with littermate controls. (C) Administration of IL-20 to normal mice increased multipotential progenitors. The IL-20 group received 5 μg IL-20 per animal twice daily for 10 days. Control vehicle groups received a similar number of PBS injections. Data represent means ± SD for 10 animals per group. Each mouse was evaluated separately. *P < .02 compared with littermate controls.