Virus-like particles in geometric tubuloreticular structures.

Tubuloreticular structures of the geometric type were observed in dog osteosarcoma cells (D17a) before and after cocultivation with human placenta cells and before and after passage of the cocultivated cells through NIH nude mice. After passage through NIH nude mice, the reestablished cultures regularly produced conventional murine type-C particles and displayed budding virus-like particles (VLP) within the tubuloreticular structures. VLP, tentatively considered an aberrant form of type-C particles, were presumably of murine origin since they were not observed in the osteosarcoma cells before passage through NIH nude mice.