The response of Slj/+ mice to experimental manipulation of the erythron

We have compared the response of mice heterozygous for the Slj allele-which have a stromal defect resulting in mild macrocytic anemia-and their normal +/+ littermates to manipulations of the erythron to further characterize the effects of the Slj allele on hemopoiesis. CFU-S kinetics in Slj/+ mice following plethorization or induction of anemia did not differ from similarly treated +/+ littermates. Under all circumstances, however, Slj/+ mice had a smaller splenic CFU-S population than similarly treated +/+ mice. Slj/+ and +/+ mice responded similarly to induction of hemolytic anemia with a large rise in 59Fe incorporation in spleen and blood. Hypertransfused Slj/+ mice were shown to have a diminished response to exogenous erythropoietin in spleen and blood as compared with their +/+ littermates. We conclude that the regulation of CFU-S kinetics in mutant Slj/+ mice is not anomalous as has been reported to be the case in Sl/Sld mice. The defective stromal tissue of Slj/+ mice, however, does not support a normal-sized CFU-S population, which leads to decreased influx of progenitor cells into the erythropoietin-responsive cell compartment, causing the diminished response of plethorized Slj/+ mice to exogenous erythropoietin.