Differentiation of Rosette-Forming Cells from Myeloid Stem Cells

Abstract Evidence is presented that the myeloid and lymphoid systems of the adult mouse are derived from a common stem cell. Ionizing radiation was used to induce unique chromosome markers in individual stem cells of the myeloid system. This marked stem cell was injected into genetically anemic mice of genotype W/Wv and repopulated their myeloid systems with chromosomally marked cells. To determine whether or not cells of the lymphoid system also contained the chromosome marker, we purified rosette-forming cells from the spleens of mice bearing a marker. Mice were immunized with sheep erythrocytes (SRBC), and at the peak of the secondary immune response a spleen cell suspension was prepared. Cells in this suspension were allowed to bind SRBC and form rosettes, and the rosette-forming cells (RFC) were purified by velocity sedimentation. The RFC population appears to include all antibody-producing cells, but the converse may not be true. Karyotype analysis of the purified rosettes showed a high frequency of chromosomally marked cells, indicating that some RFC can be derived from stem cells that can also differentiate into myeloid cells. These stem cells are probably pluripotent and able to give rise to RFC of many specificities. RFC specific for SRBC were found among the progeny of all the clones examined. It is highly unlikely that stem cells with restricted specificity would give such a result. The simplest interpretation is that there exist in bone marrow of adult mice pluripotent stem cells able to differentiate into functional cells of both the myeloid and lymphoid systems.