hTERT-immortalized ovine microglia propagate natural scrapie isolates

•Ovine microglia are immortalized by telomerase (hTERT) reconstitution.•Prion permissiveness is demonstrated in four immortalized sublines.•Two sublines are permissive to natural scrapie isolates derived from sheep.•PrPC levels are insufficient to predict permissiveness to PrPSc in hTERT-microglia. Ex vivo propagation of natural prion isolates (i.e., propagated solely in the natural host) is crucial for the characterization and study of transmissible spongiform encephalopathies (TSEs). Several well-established, prion-permissive cell culture systems are available; however, only a few cell lines are permissive to natural prion isolates and these cells are not pathophysiologically relevant (e.g., renal epithelium and fibroblast-like cells). Therefore, a pathophysiologically relevant cell line derived from a natural TSE host could be used for propagation of natural prion isolates. In this study, ovine brain macrophages (microglia) were immortalized by transfection with the human telomerase reverse transcriptase (hTERT) gene to identify cell lines (hTERT-microglia) permissive to natural scrapie prion isolates. Following transfection, hTERT-microglia were passaged up to 100 times and their lifespan was significantly longer compared to parental cells (Fisher's exact test, P