MAV-2-O replicates at a reduced rate in cells from the osteopetrosis resistant G-B1 chicken.

The replication of the avian osteopetrosis virus MAV-2-O was compared in chick embryo fibroblasts from two strains of chicken. These were G-B1 which is relatively resistant to MAV-2-O and CB which is susceptible. The production of MAV-2-O was delayed in G-B1 cells (compared with CB cells). The same result was observed after infection with Rous sarcoma viruses of subgroups B, C, and D. In addition, the transforming viruses induced foci on G-B1 fibroblasts 24 to 48 hours later than on CB fibroblasts. In G-B1 cells there was also a delayed kinetics of intracellular viral RNA production. Integrated and linear unintegrated MAV-2-O DNA species were also present in lower amounts in G-B1 than in CB fibroblasts at 3 days postinfection. In vivo studies confirmed the in vitro situation. There was a marked difference in the amount of virus present in the osteoid bone matrix and the osteocytic lacunae of osteopetrotic bones from susceptible and G-B1 chickens. In contrast to the bone lesions from susceptible animals, budding virus particles were not detectable in lesions from G-B1 chickens. There was no difference in the amount of virus in osteopetrotic and non-osteopetrotic bone of susceptible chickens suggesting that virus replication alone is not sufficient for induction of osteopetrosis and that an additional specific virus-cell interaction is required. The relative resistance of strain G-B1 may therefore, be a consequence of a reduced frequency of this interaction. Its basis may be the lower amount of integrated, as well as unintegrated, viral DNA.