Label-free digital holo-tomographic microscopy reveals virus-induced cytopathic effects in live cells

Abstract

Cytopathic effects (CPEs) are a hallmark of infections. CPEs can be observed by phase contrast or fluorescence light microscopy, albeit at the cost of phototoxicity. We report that digital holo-tomographic microscopy (DHTM) reveals distinct patterns of virus infections in live cells with minimal perturbation. DHTM is label-free, and records the phase shift of low energy light passing through the specimen on a transparent surface. DHTM infers a 3-dimensional (3D) tomogram based on the refractive index (RI). By measuring RI and computing the refractive index gradient (RIG) values DHTM unveils on optical heterogeneity in cells upon virus infection. We find that vaccinia virus (VACV), herpes simplex virus (HSV) and rhinovirus (RV) infections progressively and distinctly increased RIG. VACV, but not HSV and RV infection induced oscillations of cell volume, while all three viruses altered cytoplasmic membrane dynamics, and induced apoptotic features akin to the chemical compound staurosporin, but with virus-specific signatures. In sum, we introduce DHTM for quantitative label-free microscopy in infection research, and uncover virus-type specific changes and CPE in living cells at minimal interference.