Phenylhydrazine-induced extramedullary erythropoiesis in Lyn^-/- mice is enhanced but does not assist recovery from anemia. (A) Lyn^+/+ and Lyn^-/- mice (8-12 weeks) were treated with phenylhydrazine (PHZ). At day 3.5, splenocyte preparations were assayed for frequencies of Ter119^pos erythroblasts. Data shown (including several-fold increases in CD71^pos and Ter119^posLyn^-/- erythroblasts) are representative of 3 independent experiments (Table 1). (B-C) Frequencies of splenic CFUe's and BFUe's also were determined for phenyhydrazine-treated Lyn^-/- and control mice (means ± SD, n = 3) together with increases in spleen weight (means ± SE, n = 3 per group). (D) Possible effects of enhanced splenic erythropoiesis in phenylhydrazine-treated Lyn^-/- mice on red cell mass were assessed based on mean hematocrits (± SE, n = 6). For comparison, mice expressing a knocked-in EpoR-H allele also were analyzed. For EpoR-H mice (but not Lyn^-/- mice), mean hematocrits at day 15 differed significantly from wild-type controls. ^*P < .01.