STAT3 regulates HPC homeostasis in bone marrow and spleen. (A) Bone marrow (top) or spleen (middle) cells were analyzed for hematopoietic progenitor cell numbers and bone marrow cells for cycling status (bottom) from wild-type or Stat3^CD4−/− mice. Results are the average ± SEM of 6 Stat3^CD4−/− and littermate control (WT) mice, all individually assessed from a total of 2 separate experiments. (B-C) Bone marrow (top) or spleen (middle) cells were analyzed for hematopoietic progenitor cell numbers and bone marrow cells for cycling status (bottom) from wild-type and Il17^−/− mice (B) or wild-type and Rorc^gfp/gfp mice (C). Results are the average ± SEM of 3 Il17^−/− and Balb/c (WT) mice, all individually assessed and representative of a total of 3 separate experiments (B), or 4 Rorc^gfp/gfp and 4 C57BL/6 mice all individually assessed (C). Unless indicated, SEM of the percentage of progenitors in S-phase was < 3%. Asterisks indicate significant difference from wild-type mice: *P < .04; **P < .001. Statistics were performed using the Student t test.