Low doses of IL-9 accelerate platelet recovery after chemotherapy-induced thrombocytopenia. (A) C57BL/6 mice (2 months old) were injected with carboplatin (100 mg/kg); 8 days later, mice were treated with IL-9 (IP, 2.5 µg/kg per day) for another 8 days and platelet numbers were counted (n = 10, 1-way ANOVA). (B) MK counts in mice (n = 10, 1-way ANOVA). Data are representative of 3 independent experiments and are represented as mean ± SD. *P < .05; **P < .01; ***P < .001. (C) Schematic model for regulation of megakaryocyte formation by osteoblast through secretion of IL-9. IRs, insulin receptor substrates.