The relationship between feathering abnormalities ("nakanuke") and tumour production in chickens inoculated with reticuloendotheliosis virus.

High concentrations of T strain reticuloendotheliosis virus (REV), which had been maintained by passage in 1-day-old chicks, produced reticuloendotheliosis tumours and deaths 8 to 13 days after inoculation. At lower concentrations fo virus inoculum, deaths did not occur but feathering abnormalities ("nakanuke") was regularly produced. These results indicate that the oncogenic T strain of REV may also produce abnormal feathering. The oncogenic potential was decreased when REV-T strain maintained in 1-day-old chicks was passaged once in duck embryo fibroblast (DEF) cultures. After three passages in DEF cultures the same virus strain had lost oncogenicity but retained the ability to induce abnormal feathering. REV-T strains which had been maintained over long periods in chicken embryo fibroblast (CEF) cell culture also lacked oncogenic potential but produced abnormal feathering in chickens. Tumours were not produced during a 2-month observation period by either REV-T which had been passaged three times in DEF culture or by the Japanese KI strain of REV which is not known to be oncogenic, but abnormal feathering was induced in both groups of inoculated chickens. Serological differences were not detectable with the indirect fluorescent antibody test among strains of REV with and without oncogenic potential.