Ebola virus infection inversely correlates with the overall expression levels of promyelocytic leukaemia (PML) protein in cultured cells

We found that two cell lines, Vero E6 and MCF7, support virus production at high and low levels respectively. The expression of viral proteins was visualized and quantified using high resolution immunofluorescence microscopy. Ebola encoded NP and VP35 accumulated in cytoplasmic inclusion bodies whereas VP40 was mainly membrane associated but it was also present diffusely in the cytoplasm as well as in the euchromatic areas of the nucleus. The anti-VP40 antibody also allowed the detection of extracellular virions. Interferon-alpha treatment decreased the production of all three viral proteins and delayed the development of cytopathic effects in both cell lines. Virus infection and interferon-alpha treatment induced high levels of PML protein expression in MCF7 but much less in Vero E6 cells. No disruption of PML bodies, a common phenomenon induced by a variety of different viruses, was observed.We have established a simple fixation and immunofluorescence staining procedure that allows specific co-detection and precise sub-cellular localization of the PML nuclear bodies and the Ebola virus encoded proteins NP, VP35 and VP40 in formaldehyde treated cells. Interferon-alpha treatment delays virus production in vitro. Intact PML bodies may play an anti-viral role in Ebola infected cells.Ebola virus belongs to the family of negative strand RNA viruses (Mononegavirales) and together with the Marburg virus are the two known species of the Filoviridae family [1]. Electron microscopy of Ebola virions produced in cell culture have shown them to be pleomorphic, appearing as either 6-shaped, circular or as long filamentous (and sometimes branched) forms with a length up to 14,000 nm and a uniform diameter of 80 nm [2]. The 19 kb single-stranded RNA genome encodes seven viral proteins: the membrane associated (matrix) proteins VP24 and VP40, the viral glycoproteins, GP (that forms the 10 nm long peplomers) and sGP (non-structural secreted form), the characteristic helical ribonucl