Lyn^-/- mice exhibit normal hematocrit recovery following phenylhydrazine challenge but show enhanced erythroid progenitor expansion. (A) Changes in hematocrit and percentages of reticulocytes over a 17-day period were assessed in Lyn^+/+ and Lyn^-/- mice after 2 consecutive intraperitoneal injections of phenylhydrazine (60 mg/kg) on days 1 and 2. Mean hematocrit (squares) and reticulocyte (circles) values for 3 to 8 mice per time point (± SD) are shown. (B) Changes in spleen weights in Lyn^+/+ and Lyn^-/- mice were recorded following phenylhydrazine challenge. Values represent the mean (± SD) for 3 to 5 mice per time point, excepting days 5 to 7, where 6 to 19 mice per point are shown. (C) Representative 2-color FACS profiles of spleen cell populations from phenylhydrazine-treated Lyn^+/+ and Lyn^-/- mice stained with the mAbs CD71 and Ter119. Mature RBCs and PI-positive cells were excluded from the analysis. (D) Numbers of splenic CFU-e's and BFU-e's in Lyn^+/+ and Lyn^-/- mice were determined 3, 6, and 9 days after phenylhydrazine challenge. Values are the mean (± SD) of 5 mice per genotype. (E) The response of SHIP-1^+/+ and SHIP-1^-/- mice to phenylhydrazine challenge was determined by assessing reticulocyte and hematocrit levels at days 0, 3, and 6 after challenge. Values are the mean (± SD) of 4 mice per genotype. (F) Numbers of splenic CFU-e's in SHIP-1^+/+ (▪) and SHIP-1^-/- mice (□) were determined 3 and 6 days after phenylhydrazine challenge. Values are the mean (± SD) of 4 mice/genotype.