Low doses of IL-9 prevent chemotherapy-induced thrombocytopenia. (A) BALB/c and C57BL/6 mice (2 months old) were injected with carboplatin (100 mg/kg) followed by daily injection with IL-9 (1, 2.5, or 7.5 µg/kg per day), TPO (100 µg/kg per day), or IL-11 (100 µg/kg per day) starting on the second day for 8 days. IL-9-1, 2, and 3 represent the dose of 1, 2.5, and 7.5 µg/kg per day, respectively. Mean platelet count was determined (n = 10, 1-way ANOVA). (B) MK counts in mice (n = 10, 1-way ANOVA). (C) FACS analysis of proliferation rate of MK progenitor cells (CD41⁺Sca-1⁺Edu⁺) in BM of treated mice (n = 6, Student unpaired t test). (D) Quantification analysis of CD41⁺Sca-1⁺Edu⁺ cells in (C) (n = 6, Student unpaired t test). Data are representative of 3 independent experiments and are represented as mean ± SD. *P < .05; **P < .01; ***P < .001.