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Target cells for avian myeloblastosis virus in embryonic yolk sac and relationship of cell differentiation to cell transformation

The yolk sac of the 12-day chicken embryo retains the blast stage progenitors to cells of the myeloid lineages with a very low level of contamination by more mature myeloid cells which have begun to express the characteristic myeloid cell markers. Both in vivo and in vitro experiments have supported the hypothesis that target cells for the BAI-A strain of avian myeloblastosis virus are contained within the myeloid lineages. An assay system for avian myeloblastosis virus was developed which utilizes this yolk sac cell system and which appears to be more sensitive than previous published assays. In addition, the kinetics of a liquid culture transformation system is presented in which at least 4% of the yolk sac cell population was transformed in a relatively synchronous fashion at 2 days after infection. The morphological transformation preceded an increased rate of cell proliferation. Cell separation procedures provided a 10- to 20-fold enrichment of target cells and demonstrated that the target cell population copurifies with macrophage colony-forming cells which are the committed progenitors to the macrophage lineage. In combination with earlier work, this work demonstrated that cells committed to the macrophage lineage at all stages of differentiation may serve as target cells for infection by avian myeloblastosis virus.