Assay of avian leukosis viruses by indirect immunoperoxidase method.

Chick embryo fibroblast cells (CEF) infected with avian leukosis viruses were stained selectively by the indirect immunoperoxidase method. Good results were obtained by the use of a successive combination of periodate-lysine-paraformaldehyde fixation and diaminobenzidine reaction mixture. Viral antigens were detected type-specifically on infected cells. Type-specific antisera determined by the neutralization test were absorbed by the homologous type of virus-infected CEF, but not by the heterologous type of these cells. This test was more effective for detecting virus infectivity than the resistance-inducing factor test. Viral antigen was observed 2 days after inoculation with a large amount of the virus. The minimum infective dose of the virus for the antigen detection was 100 resistance-inducing units (RIU) per plate 4 days after infection, or 1 RIU per plate in CEF after two passages.