STAT3 controls hematopoietic progenitor responses during L monocytogenes infection. Wild-type (WT) or STAT3-deficient (KO) mice were infected with 20 000 colony-forming units of L monocytogenes by intravenous injection. (A) Immature Gr-1^lo (Gr-1^lo) and mature Gr-1^hi (Gr-1^hi) granulocytes were isolated from untreated controls (NT) or L monocytogenes–infected mice at 12 or 24 hours after infection, as indicated. Tyrosine-phosphorylated and total STAT3 was detected by immunoblotting, as shown. Data are representative of 3 independent experiments. (B) The frequency of LSKs was determined 12 hours after infection or in untreated controls (NT), as indicated. Results from a representative experiment (1 of 4) are shown. (C) LSK proportions within individual mice is indicated for untreated (−) or infected (+) WT or STAT3-deficient animals. The horizontal bar indicates average values, determined from 4 independent experiments. (D) Absolute numbers of LSKs in 2 femurs and 2 tibiae from untreated (−) or infected (+) mice were determined by enumeration (n = 7 for untreated WT; n = 6 for infected WT; n = 4 for untreated or infected KO). Average values are shown, determined from 4 independent experiments. (C-D) Error bars represent SEM. *P < .05 compared with untreated controls.