Infectiousness of the virus in Shope papillomas induced or grown in the variant rabbit strain and in a resistant species.

In the great majority of cases, the pathogenicity of the Shope papilloma virus is lost after transfer from cottontail to domestic rabbits. There is adequate evidence that the virus is present in the papillomas arising in domestic rabbits, for such animals develop neutralizing and complementfixing antibodies. :Further, the intraperitoneal inoculation of extracts of noninfectious papillomas results in the production of antibody and in resistance to reinfection (4, 5). I t has been concluded, on this basis, that the virus exists in an altered or "masked" form, but the nature or mechanism of the masking process is not understood. Evidence has been obtained to suggest that antibody is concerned in the phenomenon (8), but the significance of its action is questionable in view of the high titcr found in cottontail rabbits bearing infectious papillomas. The experiments to be presented were carried out to determine whether the masking effect was dependent on the body fluids of the domestic rabbit or on the constitution of the epithelial cells harboring the virus. To this end, papillomas derived from cottontail and domestic rabbit skin were tested for the presence of infectious virus after induction in or transplantation to the variant strain.