Virus release by cell colonies derived from chickens and cultures infected with avian myeloblastosis virus.

More than 90% of 3-week-old clones obtained from avian myeloblastosis virus (AMV)-induced myeloblasts differenti ate into mature cells when grown as colonies in semisolid medium. This was determined primarily by assaying colo nies on resistant cell feeder layers for the presence of myeloblasts. These colonies were also seeded onto suscepti ble cell feeder layers to assay for the presence of transform ing AMV. No correlation was found between the presence or absence of virus and the degree of differentiation of the colony. Of 131 myeloblast colonies placed on susceptible cell feeder layers, 121 were found to produce proliferating myeloblasts. The 10 negative colonies were also negative for AMV. Myeloblastosis-associated viruses, however, were recovered from all 10. Of 102 myeloblast-positive colonies tested, 84 were found to produce transforming AMV as well as associated viruses. The remaining 18 released no AMV although myeloblastosis-associated viruses were recovered in each case. In summary, most clones were myeloblast positive and AMV positive. Approximately 18%, however, were myeloblast positive and AMV negative, and approxi mately 8% were myeloblast negative and AMV negative. Normal colony-forming cells were often present in leukemic buffy coats. These produced colonies of the dispersed type (type I) and contained mainly macrophages. They did not release AMV and did not contain myeloblasts although myeloblastosis-associated viruses were released.