Host-pathogen interaction: study of Toscana virus

The Bunyaviridae is a large family of RNA viruses distributed worldwide, transmitted to vertebrate hosts by arthropods (arbo-bunyaviruses) which can cause severe pathologies in humans and livestock (Léger & Lozach 2015). Due to climate changes and diffusion of competent arthropods worldwide, arbo-bunyaviruses have become pathogens of major medical importance (Briant et al. 2014). While the majority of arbo-bunyavirus infections do not lead to neuroinvasive forms of disease, they are among the most severe infectious risks to the health of the human central nervous system (CNS) (Salimi et al. 2016). Yet transmission, tropism, receptors and cell entry remain poorly characterized (Léger & Lozach 2015). Nowadays, Toscana virus (TOSV) a Phlebovirus belonging to the Bunyaviridae family, is considered an emergent pathogen associated with acute neurological disease, such as meningitis, meningoencephalitis and encephalitis, occurring in the Mediterranean countries (principally Italy, Spain, France) during the summer months (Valassina et al. 2003 a; Valassina et al. 2003 b; Charrel et al. 2005; Sanbonmatsu –Gàmez et al. 2009; Cusi et al. 2010). The cellular receptors employed by TOSV, for host-cell entry, have not been identified so far, and the paucity of information on virus host interactions during the first stages of infection may limit therapeutic and preventive approaches (Hofmann & Pohlmann 2011). During natural transmission, TOSV is introduced into the skin through bites of infected arthropods. In this PhD project, we determined the role of dermal dendritic cells and their influence in the activation of humoral response after TOSV infection. Moreover, by in vitro and in vivo studies we investigated the role of endothelial cells in the maintenance of viremia and their involvement in viral neuroinvasion. Finally, to better understand the mechanisms of virus-host interaction, we focused our attention on viral glycoproteins. In this field, studies on immunological response and immunological memory of subjects infected by TOSV, could be useful to identify the correlates of protection. In particular, we tried to identify the viral glycoproteins’ epitopes recognized by neutralizing antibodies. By immortalization of human memory B cells (Traggiai et al. 2004) and the “high throughput method”, we were able to identify specific antibodies reacting with different epitopes of the viral envelope glycoproteins.