Morphological study of virus-like particles in two transplantable tumours from BDX rats

Virus-like particles were found in two transplantable tumours, Sp56 and Sp6, from BDX rats. Sp56, a neurogenic sarcoma, contains abundant C-type particles in all stadia nof morphogeneis. This tumour reacts with anti-Friend leukaemia virus gp70 and anti-Rauscher leukaemia virus p30 sera. Sp6, a fibrosarcoma, has abundant virus-like particles in the cytoplasm, very often associated with centrioles or basal bodies of a cilium. These particles consist of two concentric shells with a diam. of 60 to 65 nm. Released particles were found outside the cell with a diam. of 85 to 100 nm characterized by an envelope and an eccentrically located electron-dense nucleoid, surrounded by an intermediate layer. These virus-like particles show no cross-reaction with antisera against murine C- or B-type particles, but show ultrastructural similarity with virus particles recently described in Chinese hamster cells and in mouse cell lines infected with two retrovirus isolates from South-East Asian mice.