Morphogenesis of rabbit fibroma virus. Correlation with pathogenesis of the skin lesion.

Rabbit fibroma virus injected into the dermis of adult rabbit skin evokes an inflammatory, then granulomatous and finally proliferative or tumoral response. About 1 week after injection, the grossly visible nodular lesion reaches its maximum size and regresses, becoming hemorrhagic and necrotic. Unlike vacciiia, the morphogenesis of the RFV has not been validated satisfactorily. The present study shows that RFV-infected cells contain all the evolutive forms that have been identified during the course of vaccinia virus replication. In addition, long, twisting, intracytoplasmic lamellated inclusions were found in infected cells. These lamellae were composed of linear arrays of elongated, electron-dense fibers. When the inclusion was sectioned in a plane perpendicular to the fiber, the latter was found to be covered by projections approximately 160 A long, spaced at intervals of approximately 80-90 A; when sectioned tangentially, the lamellae appeared to be composed of tubules. Evidence is presented showing the similarities between the subunit of the lamellated inclusion and the virus membrane. It seems likely, therefore, that the viral membrane is covered by closely packed tubules approximately 160 A long. The lambellar inclusion is thought to represent abnormal synthesis or excessive formation of viral membranes. In addition to lamellae, which probably indicate some defect in virogenesis, some infected cells contained viral membranes partially or completely encircling the host's cell constituents, or fragments of viral membrane instead of viral matrix. Furthermore, structures resembling virus nucleoid were lying free in the viral or cytoplasmic matrix. The course of viral morphogenesis was correlated with viral multiplication and the kinetics of interferon production at the site of viral inoculation in the rabbit skin.