Abstract:

Supernatants from Vero cells persistently infected with Junin virus interfered with cytolytic and lethal activities of standard virus. Two Vero cell sublines, chronically infected with Junin virus named VRJ1 and VRJ3, were obtained after prolonged cultivation of cells which survived primary infection. VRJ1 was maintained over a period of 48 days, by biweekly serial transfers while VRJ3, similarly treated, was cultivated for 385 days. One of the characteristics of these cell lines was resistance against superinfection with homologous virus that ordinarily produced CPE and plaques in normal Vero cells; the cells were then considered chronically infected. Supernatants taken at different cell passage levels were tested for their interference activity after centrifugation to eliminate floating cells and debris. The degree of CPE intensity caused by inoculation of Vero cells with 104, 105 or 106 TCID50 of standard virus was markedly depressed by coinfection with supernatant from passage 3 of VRJ3 (VRJ1p1); VRJ1p1 supernatant also had interference activity as shown by coinfection with standard virus and expressed by plaque forming inhibition. The plaque production of standard virus was inhibited by coinfection with VRJ1p1 supernatant which did not originate plaques when inoculated alone. The interference capacity of VRJ1p6 supernatant was reduced coincidentally with the formation of 55 PFU/ml. Interference activity was neutralized by Junin specific antiserum and inhibited by chloroform treatment. When Vero cells infected with RVJ1p6 supernatant were challenged with standard virus 72 hs later, an inhibition of 98% was achieved in contrast with value of 35% showed in Table 1. All interference assays performed in vivo were done with supernatant from VRJ3p79. Figure 2 shows that coinfection of suckling mice with both, supernatant and standard virus, delayed and reduced mortality in comparison with control animals inoculated with standard virus alone. However, the interference effect was more evident if the mice were challenged 24 hs later. Supernatant from VRJ3p79 was non pathogenic for suckling mice. Two main factors may be responsible for the maintenance of chronic infections: interferon or synthesis of defective particles. It is assumed that interferon is not the factor because VRJ1 and VRJ3 cells can support the growth of VSV with an EOP of 1.04. Furthermore, the interfering activity was abolished by specific anti Junin immune serum or by chloroform treatment, indicating that interference is probably due to the presence of particles of virus nature. The regulation of chronic infection with Junin virus in Vero cells seems to be identical with the ones described for other Arenaviruses, where defective interfering particles are involved.