Figure 1

Friend erythroleukemia is a two-step disease. The target cell for SFFV is a late BFU-E or a CFU-E. SFFV infection induces the proliferation of proerythroblastic cells that differentiate into erythrocytes in the absence of Epo, in the case of FLV-P infection. The second step is characterized by the outgrowth of Friend tumor cells that can be serially transplanted into mice and cultured as permanent cell lines without growth factor. The tumor cells are blocked in differentiation, but can be induced to differentiate along the erythroid pathway by chemical inducers. A pellet of red blood cells derived from a Friend tumor cell line treated for 5 days with DMSO is shown in the box.