Virology is the study of the biology of viruses and viral diseases. As obligate intracellular parasites, viruses hijack the molecular machinery of host cells and use it to produce new viral particles.
Although live-cell imaging cannot be used for direct visualization of viruses due to their small size (20 – 300 nm) and the limitations imposed by light microscopy itself, this technique greatly facilitates the understanding of complex virus-host interactions. Live-cell microscopy can be used for visualizing and quantifying morphological and functional changes caused by virus infection, known as viral cytopathic effects (CPE). Some viruses only cause subtle cellular changes, while other viruses lyse the cells and destroy the host cell monolayer. Continuous imaging of infected cells can detect the whole range of these virus-induced cellular changes in vitro, allowing to study the progression of viral infections as well as to screen new antiviral drugs and vaccines.
Live-cell imaging in BSL-3/4 laboratories
Biosafety level (BSL)-3 and 4 laboratories are high-containment facilities designed for the research of highly pathogenic viruses and bacteria. These include SARS-CoV-2, the causative agent of COVID-19, Mycobacterium tuberculosis, and Ebola virus, among many others. BSL-3 and 4 facilities play a central role in diagnostics and treatment development against world’s most dangerous microorganisms, however working in these facilities presents a number of challenges. Despite implemented health and safety measures, the researchers are still subjected to a substantial risk of contracting a life-threatening disease. In addition, the high cost of disposable protective equipment, and the time and labor associated with performing BSL-3/4-based experiments, impose further limitations on the researchers.
Remote monitoring of cell cultures reduces the time spent in the BSL-3/4 laboratories. It is also a much more cost-efficient alternative, as there is no need to use expensive protective equipment when analyzing the cells remotely. Once infected with the virus, the cell cultures can be placed inside the incubator and safely monitored via the CytoSMART live-cell imaging devices, minimizing the exposure of researchers to biological hazards. The images and time-lapse videos can be immediately accessed via the CytoSMART Cloud, providing real-time updates on the cell cultures and running experiments.
Non-endpoint analysis of viral cytopathic effects
Viral cytopathic effects (CPE) commonly include rounding, detaching, and clumping of adherent infected cells, leading to the formation of holes in a confluent cell monolayer. Conventional methods of CPE analysis (e.g. plaque and focus-forming assays) are typically the end-point virology assays that involve manual examination of CPE using brightfield microscopy, making it a labor-intensive, time-consuming, and user-dependent approach. The CytoSMART devices, including the CytoSMART Omni and Lux3 FL, can analyze CPE in real time, using both brightfield and fluorescence imaging. The occurrence of CPE can be monitored for days or weeks at a time, without missing any critical stages in the development of virus-induced CPE. In addition, the images and time-lapse movies are acquired and analyzed automatically. For example, the reduction in host cell count can be measured using the AI-based confluence algorithm, eliminating any subjectivity and bias in results interpretation.