Abstract
Transmissible gastroenteritis virus (TGEV) is a porcine coronavirus. Lithium chloride (LiCl) has been found to be effective against several DNA viruses, such as Herpes simplex virus and vaccinia virus. Recently, we and others have reported the inhibitory effect of LiCl on avian infectious bronchitis coronavirus (IBV) infection, an RNA virus. In the current study, the action mechanism of LiCl on cell infection by TGEV was investigated. Plaque assays and 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenyl tetrazoliumbromide (MTT) assays showed that the cell infection by TGEV was inhibited in a dose-dependent manner, when LiCl was added to virus-infected cells; the cell infection was not affected when either cells or viruses were pretreated with the drug. The inhibition of TGEV infection in vitro by LiCl was observed at different virus doses and with different cell lines. The inhibitory effect of LiCl against TGEV infection and transcription was confirmed by RT-PCR and real-time PCR targeting viral S and 3CL-protease genes. The time-of-addition effect of the drug on TGEV infection indicated that LiCl acted on the initial and late stage of TGEV infection. The production of virus was not detected at 36 h post-infection due to the drug treatment. Moreover, immunofluorescence (IF) and flow cytometry analyses based on staining of Annexin V and propidium iodide staining of nuclei indicated that early and late cell apoptosis induced by TGEV was inhibited efficiently. The ability of LiCl to inhibit apoptosis was investigated by IF analysis of caspase-3 expression. Our data indicate that LiCl inhibits TGEV infection by exerting an anti-apoptotic effect. The inhibitory effect of LiCl was also observed with porcine epidemic diarrhea coronavirus. Together with other reports concerning the inhibitory effect of lithium salts on IBV in cell culture, our results indicate that LiCl may be a potent agent against porcine and avian coronaviruses.
Highlights
Transmissible gastroenteritis virus (TGEV) belongs to the family Coronaviridae and is one of the most important causative agents of enteric infections in pigs
The appearance of porcine respiratory coronavirus (PRCoV), a respiratory mutant of TGEV has drastically decreased the risk of TGE in Europe, since neutralizing antibodies elicited by the avirulent PRCoV can provide cross-protection against TGEV infection [10]
In addition to enhancement of vaccine safety and efficacy, development of potential antivirals is a complementary approach in the future strategy for preventing TGEV infection
Summary
Transmissible gastroenteritis virus (TGEV) belongs to the family Coronaviridae and is one of the most important causative agents of enteric infections in pigs. TGEV is an enveloped virus with a positive-stranded RNA genome approximately 28.5-kb in size, and it consists of four structural proteins: the spike (S), the integral membrane (M) glycoprotein, and the nucleocapsid (N) protein [1,4,5]. The 39 third of the genome contains the genes encoding the structural and some nonstructural proteins (59-S-3a-3b-E-MN-7-39) [6]. The glycoprotein S is primarily responsible for inducing neutralizing antibodies and for initiating infection [7,8,9]. The appearance of porcine respiratory coronavirus (PRCoV), a respiratory mutant of TGEV has drastically decreased the risk of TGE in Europe, since neutralizing antibodies elicited by the avirulent PRCoV can provide cross-protection against TGEV infection [10]. TGE prevalence is still reported and some TGEVs have been isolated in different parts of the world, e.g. in various geographical locations in China, implying that TGEV infection is still threatening pig industry [11,12,13,14]
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