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Target cell specificity of defective avian leukemia viruses: hematopoietic target cells for a given virus type can be infected but not transformed by strains of a different type.

Defective avian leukemia viruses of the avian erythroblastosis (AEV), avian myelocytomatosis (MC29), and avian myeloblastosis (AMV) type induce the proliferation of leukemic cells with properties of erythroblasts, macrophages, and myeloblasts, respectively. Their target cells can be separated and have properties of cells of the erythroid (AEV) and myeloid lineage (MC29 and AMV), respectively. In the present study we have shown that this target cell specificity is not due to the ability of the different strains to infect only certain types of hematopoietic cells. Instead, AEV was found to replicate in macrophages and to induce the expression of p75 AEV, its presumptive transforming protein. Likewise, MC29 was found to replicate in AEV-infected erythroblasts as well as in AMV-infected myeloblasts and to express the p110 MC29 protein in these cells. Superinfection with MC29 or AMV of ts34 AEV-infected erythroblasts did not impair their capacity to accumulate hemoglobin after shift to nonpermissive temperature. Our results support a model in which the transforming proteins of AEV, MC29, and MAV block the differentiation of their target cells by competitively inhibiting the action of a hypothetical homologous cellular differentiation protein synthesized in the corresponding target cells only.