Murine Norovirus Transcytosis across an In Vitro Polarized Murine Intestinal Epithelial Monolayer Is Mediated by M-Like Cells

Noroviruses (NoVs) are the causative agent of the vast majority of nonbacterial gastroenteritis worldwide. Due to the inability to culture human NoVs and the inability to orally infect a small animal model, little is known about the initial steps of viral entry. One particular step that is not understood is how NoVs breach the intestinal epithelial barrier. Murine NoV (MNV) is the only NoV that can be propagated in vitro by infecting murine macrophages and dendritic cells, making this virus an attractive model for studies of different aspects of NoV biology. Polarized murine intestinal epithelial mIC(cl2) cells were used to investigate how MNV interacts with and crosses the intestinal epithelium. In this in vitro model of the follicle-associated epithelium (FAE), MNV is transported across the polarized cell monolayer in the absence of viral replication or disruption of tight junctions by a distinct epithelial cell with microfold (M) cell properties. In addition to transporting MNV, these M-like cells also transcytose microbeads and express an IgA receptor. Interestingly, B myeloma cells cultured in the basolateral compartment underlying the epithelial monolayer did not alter the number of M-like cells but increased their transcytotic activity. Our data demonstrate that MNV can cross an intact intestinal epithelial monolayer in vitro by hijacking the M-like cells' intrinsic transcytotic pathway and suggest a potential mechanism for MNV entry into the host.