Vero cells persistently infected with tacaribe virus: role of interfering particles in the establishment of the infection

Abstract

Eight Vero cell sublines (Vero T) persistently infected with wild type Tacaribe virus replicated in different hosts were established. In order to unravel the mecha- nism involved in the initiation and maintenance of persistence, the properties of virus shed by the sublines and the presence of interfering particles (IP) were analyzed. During the course of infection, persistent virus (Tac-pi) underwent muta- tions although no consistent pattern of virus evolution was observed, ts mutants were isolated from two Vero T sublines, whereas a slow growth variant was shed by another. The remaining sublines released virus resembling wt parental virus. Except for Vero T 1 sublines, Vero T cultures shed no detectable IP. These results emphasize the point that neither the emergence of virus mutants nor the synthesis of IP is essential for the maintenance of the persistent state. To define the role of IP in the initiation of persistence, coinfection experiments with a characterized inoculum were performed. For that purpose, attempts were made to obtain IP stocks free from pfu by serial transfers of undiluted virus. Neither enrichment nor amplification of IP occurred, and virus stocks were freed of infectious virus by UV irradiation. If normal Vero cells were infected with Tac-pi virus released by Vero T 2, Vero T 3, Vero T 4, Vero T 5, Vero T 6, Vero T 7 and Vero T 10 sublines, a complete destruction of the monolayer without cell recovery was ob- served. In contrast, parental and Vero T 1 viruses always originated persistently infected sublines. Similarly, the addition of IP to virus inocula constituted by Tac-pi viruses released by Vero T 2, Vero T 3, Vero T 4, Vero T 5, Vero T 6, Vero T 7 and Vero T 10 sublines gave rise to persistently infected cultures. These results suggest that although IP are not important by themselves in the maintenance of persistence, they play a major role in initiation.