IL-19 prevented chloramphenicol-induced neutropenia. (A) Two-month-old C57BL/6 male mice were injected with chloramphenicol (200 mg/kg per day) followed by injection of IL-19-1 (25 µg/kg), IL-19-2 (50 µg/kg), or G-CSF (100 µg/kg per day) starting from 6 days after chloramphenicol injection; mice were euthanized on day 22. The total number of neutrophils in PB was detected (mean ± SD; n = 10). (B) FACS analysis of BM and PB CD11b⁺Gr-1⁺ neutrophils in treated mice (mean ± SD; n = 10). (C) C57BL/6 mouse total BM cells were cultured with serum of patients before and after chemotherapy with cytarabine at days 3 and 7; cells were harvested on day 10. FACS analysis of CD11b⁺Gr-1⁺ neutrophils in treated BM cells (mean ± SD; n = 6). (D) The level of IL-19 in the serum of patients pre- and postchemotherapy with cytarabine (mean ± SD; n = 10). Data are mean ± SD of 3 independent experiments. (E) Schematic model of the regulation of neutrophil development by osteocytes via secretion of IL-19. **P < .01; ***P < .001.