魚類結病毒與魚類反轉錄病毒共感染時之干擾研究(一)

The aim of this study is to investigate the interference of grouper nervous necrosis
virus (GNNV) and snakehead retrovirus (SnRV) during the co-infection of the same host
cell line. A SnRV-persistent infected cell line SGF-1 was induced by inoculating the
SnRV into GF-1 cell line. The cDNA of SnRV was detected in the nucleic acid extract of
SGF-1 cells, and the genomic RNA of SnRV was also detected in the culture supernatant
of SGF-1 cells. Moreover, the supernatant of SGF-1 cells was used for the infection of
GF-1 cells, and SnRV cDNA was once again detected in infected GF-1 cells indicating
that there were infectious particles of SnRV in the supernatant of SGF-1 cells, and the life
cycle of SnRV could be completed in the SGF-1 cells. Synchronous infection of GNNV
in GF-1 cells and SGF-1 cells was done for the observation of daily changes of the
nucleic acids and the titers of the viruses. The results revealed that (1) the SnRV reverse
transcriptase (RT) could completely reverse-transcribed GNNV single-stranded RNA1
and RNA2 into cDNA during the co-infection in SGF-1 cells, and created a new cDNA
stage in the life cycle of GNNV; (2) the cDNA appeared in SGF-1 cells since the third
day after GNNV infection, and the amount of the cDNA increased as the days increased;
(3) the amount of GNNV RNA in either infected GF-1 cells or SGF-1 cells were very
similay; (4) the SnRV RNA decreased as the infection days increased; (5) the titers of the
supernatants of GNNV-infected SGF-1 cells during the third day to the fifth day
determined in GF-1 cells were very different from the titers determined in SGF-1 cells,
and the titer of the fourth day determined in GF-1 cells was 104 times higher than that
determined in SGF-1 cells. This phenomenon could be related with that the receptors of
GNNV and SnRV were available on GF-1 cells, while the receptors of SnRV were closed
on SGF-1 cells owing to the SnRV-persistent infection, and only GNNV receptors were
available on SGF-1 cells.