Antigenicity and Infectivity of Extracts of Virus-Induced Rabbit Papillomas

The antigen which binds complement when mixed with sera neutralizing the Shope papilloma-virus bears an evident relation to the virus itself; for it is present in high titer in virus-containing extracts of papillomas, it is retained by filters which hold back the virus, and its effectiveness is destroyed by the same amount of heating which renders the virus non-pathogenic. 1 The experiments now to be reported throw further light on this relation.

Tests with Extracts of Non-Infectious Papillomas and of Normal Skin. On inoculation the Shope virus gives rise to papillomas in both domestic and cottontail rabbits; yet only infrequently can it be extracted in active state from the domestic-rabbit growths, and occasionally those of cottontails fail to yield it. Papillomas from 6 cottontail and 8 domestic rabbits, which were produced by the virus yet from which it could not be recovered, have been extracted as usual and tested repeatedly for capacity to bind complement under optimal conditions. Most of these non-infectious extracts failed to bind complement, but a few bound it in a very low titer. Extracts of the normal skin of 3 cottontail rabbits also failed to bind complement, whereas the highly-infectious extracts of their naturally occurring papillomas bound it completely on concurrent test.

Antigenicity of Extracts of Non-Infectious Papillomas. Shope has found that extracts of virus-induced papillomas, which yield no active virus on extraction, will elicit virus-neutralizing antibodies when injected intraperitoneally into rabbits of homologous species. 2 He has generously sent sera from 9 domestic rabbits immunized in this way for complement-fixation tests. They bind complement when tested with suitable antigens, and their capacity to do so varies directly with their ability to neutralize the virus. The sera of 3 normal domestic rabbits failed to bind complement in the same test, as have all other normal sera tested under like conditions.