| Abstract: | Mice of the Sl/Sld genotype have an approximately 3-fold higher number of fibroblastoid progenitors (CFU-F) in their spleens than their normal +/+ littermates. Experiments were performed to determine whether the elevated Sl/Sld splenic CFU-F numbers were due to compensatory mechanisms acting in the presence of a functionally abnormal CFU-F population or to a nonspecific response to chronic anemia. Comparison of the functional ability of Sl/Sld splenic fibroblasts to produce granulocyte/macrophage colony-stimulating activity with +/+ splenic fibroblasts demonstrated that there was no difference. Similar results were obtained for Sl/Sld and +/+ femoral fibroblasts. Analysis of CFU-F in W/Wv mice revealed an approximately 3-fold higher number of splenic CFU-F than in either +/+ or heterozygous (W/+ and Wv/+) littermates. Since the anemia in W/Wv mice is attributed to a hemopoietic stem cell defect and that of the Sl/Sld mice is attributed to a microenvironmental defect, we suggest that the increased splenic CFU-F number in Sl/Sld mice is not specifically due to the microenvironmental defect, but is part of a general response to hemopoietic stress. |
