Characterization the role of key DNA sensors in herpes simplex virus replication

DNA sensors including cGAS, STING and IFI16 are key components of the innate immune response to infection. However, the precise mechanisms of action, in particular the relative importance of direct suppression of replication versus paracrine signalling of an antiviral state to susceptible cells remains unclear. We examined the kinetics of herpes simplex virus infection and spread in a relevant cell type, human keratinocytes, lacking one or other of these DNA sensors using time-lapse microscopy. We also examine transcriptional induction of interferon from the native locus, at single cell and single molecule level using highly sensitive RNA FISH. Our results reveal distinct aspects of the roles of these factors and reveal outcomes not appreciated by other methods. Cells lacking either of these factors showed increased susceptibility to initial infection (prior to any downstream paracrine signalling) but with quite different outcomes. Lack of cGAS resulted in increased cellular migration and cell density at the infection focus. On the other hand, cells lacking STING showed lower cell density and significantly increased cytopathic effect likely curtailing virus yield. Initial results demonstrate that we can analyse interferon transcription at single cell level with exquisite sensitivity down to a few transcripts per cell and reveal profound spatial heterogeneity in responses to induction by PAMP ligands. Altogether, our results reveal new insight into the spatial landscape of the initiation and spread of HSV and key cellular responses which likely integrate pathways including innate immunity, apoptosis and cell migration.