The polarity of entry and release of Canine Coronavirus from epithelial cells

Canine coronavirus (CCoV) is an enveloped, single-strand RNA virus belonging to the Alphacoronavirus genus in the Coronaviridae family Pratelli [1,2] Despite their labile nature, RNA viruses are able to rapidly adjust to negative pressures of immune system, generating novel strains that might have selective advantages over parental genomes. Epithelial cells in the gastrointestinal tracts are the target of CCoVs infection. The apical face, exposed towards the intestinal lumen, and the basolateral face have different composition and the tight junctions with neighbouring cells separate the two faces preventing mixing of membrane components. The epithelial cell surface from which viruses are released conditions the development of virus pathogenesis. Entry and release of viruses from epithelial cells can occur through either domains as a result of the distribution of viral receptors. Polarized virus release influence viral spread: basolateral release allows the infection of underlying tissues leading to a systemic infection, and apical release can limit viral spread by preventing the infection of cells other than epithelial ones. Recent study has highlighted a new pathogenetic characteristic of CCoV in vitro, which is able to infect epithelial cells from both apical and basolateral compartments, and even if with different titres, CCoV was released both in the apical and in the basolateral medium after infection. Consequently, the current view that CCoV infection is restricted to the intestine should be modified, arguing that the direction of release may be toward the blood stream inducing systemic infection.