St Louis encephalitis virus establishes a productive, cytopathic and persistent infection of Sf9 cells

Abstract

The Sf9 cell line, commonly used for gene expression by recombinant baculovirus, has been productively infected by St Louis encephalitis (SLE) virus, a flavivirus. SLE viral infection produced a c.p.e, in the SO cells characterized by giant cells and the presence of 10-fold fewer cells in the infected cultures after the first week of infection compared with uninoculated control cultures. Infected Sf9 cells expressed SLE viral antigens, and intracellular virus particles were observed by electron microscopy. Titres of cell-associated SLE virus rose slightly over an 8 week period, whereas titres of cell-free virus remained stable, suggesting that SLE virus establishes a productive and persistent infection of Sf9 cells. The SLE virus produced by the Sf9 cells could be neutralized by SLE virus-immune mouse ascitic fluid, and no evidence of escape mutants was detected. Sf9 cells persistently infected with SLE virus could be superinfected with a recombinant baculovirus and expressed recombinant antigen. The successful infection of SD cells by SLE virus represents the first report of production of c.p.e, by SLE virus in insect cells under routine cell culture conditions and of the infection of Sf9 cells by a human pathogen.

Pathogenesis of flavivirus encephalitis

“…Persistent infection in vitro and in vivo has been described in a number of experimental and clinical settings involving flaviviruses. The phenomenon of persistent infection in cell cultures of vertebrate and arthropod origin is well documented (Brinton, 1982;Chen et al, 1996;Jarman et al, 1968;Igarashi, 1979;Katz and Goldblum, 1968;Lancaster et al, 1998;Loginova et al, 1980;Poidinger et al, 1991;Hardy, 1988a, 1988b;Blair, 1977, 1979;Shah and Gadkari, 1987;Vlaycheva and Chambers, 2002;Zhang et al, 1993), and the findings are analogous to many other models of viral infections in vitro where this process can be observed. Flavivirus persistence in vitro typically arises following a cytocidal infection, with survival of a residual population of cells that harbor low levels of replicating virus for long periods of time.…”

Viral Interference and Persistence in Mosquito-Borne Flaviviruses

“…Because flaviviral infection persists for the life of the vector, the opportunities for competition or viral interference in the vector are higher than in humans, where the infection is only transient and is cleared through the immune system [ 42 ]. The evaluation of viral interference during flavivirus infection is relatively easy to detect in cell lines, and it has primarily been examined in mosquito C6/36 cells (from Aedes albopictus ) [ 12 , 23 , 30 , 31 , 35 , 39 , 41 – 48 ], TRA-171 (from Toxorhynchites amboinensis ) [ 32 ], Sf9 (from Spodoptera frugiperda ) [ 49 ], C7-10, and U4.4 cells (from Aedes albopictus ) [ 29 , 35 ]. Homologous or heterotypic, but not heterologous, viral interference is frequently observed during superinfections ( Table 2 ), and this condition is particularly evident in persistently infected cells [ 23 , 31 , 32 , 44 , 49 ].…”

Morphological changes in human neural cells following tick-borne encephalitis virus infection

“…Šenigl et al (2006) described that TBEV exhibits a trans mode of maturation in mammalian cells, but a cis mode in tick cells. This difference in the maturation process could be associated with the different characterics of CPEs observed in vertebrate and invertebrate (tick or mosquito) cells infected with flaviviruses (Zhang et al 1993; Šenigl et al, 2006; Rů žek et al, 2008). However, the maturation of TBEV observed in neuroblastoma cell lines cannot be defined as trans or cis.…”