Intracellular imaging of host-pathogen interactions using combined CARS and two-photon fluorescence microscopies.

Intracellular imaging is a key tool in the investigation of host-pathogen interactions. Advances in this area are particularly sought to understand the effect of viral infection processes on the host cell and its metabolic functions including those cases where host cell lipid metabolism is modulated as a result of infection. We demonstrate the use of combined coherent anti-Stokes Raman scattering (CARS) and two-photon fluorescence microscopies to image fibroblast cells infected by cytomegalovirus. CARS is used to image the host cell membrane, lipid droplets and morphology of the nucleus. Cell nuclei are found to expand during infection, approximately doubling in area. Some cells also show accumulations of lipid droplets at the nuclear periphery. Using a genetically modified virus strain expressing the green fluorescent protein also enables two-photon imaging of the same cells to reveal the location, nature and extent of viral protein expression.