In vivo detection of retroviral particles in mice with hybridoma induced ascites

Ascites induced by hybridoma cells following their injection into pristane-primed peritoneal cavities of BALB/c mice is often associated with the formation of intra-abdominal tumors related to the transplanted cells. These tumors and adjacent abdominal and extra-abdominal organs were excised and examined by electron microscopy. Clusters of viral particles were seen in nearly all cells composing the hybridoma tumors. The viral particles were usually present in rough ER cisternae of the transplanted tumor cells and at times were observed budding from the cisternal membranes. Individual viral units were doughnut shaped, 80-85 nm in diameter, with two concentric shells of which the outer one was more electron dense. No exogenous viral particles were detected in the peritoneally growing hybridoma cells. All non-tumor tissues examined such as liver, spleen, lung, brain and circulating WBC were free of virus. These findings provide further evidence of viral contamination of hybridomas and demonstrate the mode of persistence of such contamination when cells are placed in-vivo.