Intranuclear Inclusions in Tissue Cultures Infected With Rat Virus

Abstract

Rat virus (RV), originally isolated from tumor-bearing rats by Kilham, has many properties similar to those of polyoma virus. It has not been shown to have an oncogenic effect, however. This study was undertaken to determine the response of salivary gland of the rat to RV in tissue culture. Organotypic cultures of rat submandibular glands on gelatin sponge matrix were examined histologically at intervals from 10 to 32 days after infection with RV, and were compared with uninfected control cultures. Monolayer cultures of trypsinized rat embryo infected with RV were also examined. Type -A intranuclear inclusion bodies were found in epithelial as well as connective-tissue cells in the organotypic cultures at all time intervals under study. Similar inclusions were also found in cells of fibroblastic morphology in RV-infected monolayer cultures of rat embryo. The inclusions were similar to those previously observed in organotypic cultures of mouse salivary gland infected with polyoma virus, but tended to be larger and more eosinophilic. The response to RV was predominantly cytolytic and lacked the prolif erative aspect that is characteristic of the response of epithelium of mouse salivary gland infected with polyoma virus. Necrosis of connective-tissue cells in RV-infected cultures resulted in disruption of the organoid structure of explants, with regrouping of epithelium in atypical patterns. Macro-phage populations were decreased in RV-infected cultures. The ob-servations are consistent with the apparent, but not fully proved, lack of oncogenic activity of RV on rat salivary gland in vivo.