Application of a recombinant replicase to localize the Trionyx sinensis hemorrhagic syndrome virus and evaluate its effects on antiviral genes of T. sinensis

Trionyx sinensis Hemorrhagic Syndrome Virus (TSHSV) is an arterivirus newly discovered in Chinese softshell turtles. Little is known about the effect of antibodies against the virus or the distribution of the virus in different organs of infected turtles. In this study, a partial protein of TSHSV-HP4 was produced using a prokaryotic expression system, and its polyclonal antibody was generated. The polyclonal antibody was confirmed by western blot and dot enzyme-linked immunosorbent assay (dot-ELISA). The distribution of TSHSV in different organs of T. sinensis was examined by immunohistochemistry (IHC) and the expression of immune-related genes was analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). The results indicated that the recombinant TSHSV-HP4 protein was successfully expressed, and the generated polyclonal antibody showed specific binding to viral particles in the lung tissues of infected turtles. The IHC assay indicated that the virus was highly localized in various cells, including intestinal lymphocytes, enterocytes, kidney epithelial cells, spleen cells, lung macrophages, and cardiomyocytes. The qRT-PCR analysis revealed that TSHSV was detected in all organs tested, including the lungs, liver, kidneys, spleen, and heart. The numbers of viral mRNA copies in lung and heart tissues were significantly higher in the virus-antibody group than in the virus group. The interferon-stimulated genes (ISGs), myxovirus resistance protein 2 (MX2) and radical S-adenosyl methionine domain containing 2 (RSAD2) were highly upregulated in all groups of infected turtles. Antibody-dependent enhancement (ADE) seemed to occur after stimulation by the polyclonal antibody, because significantly greater expression of the two genes was detected in the virus-antibody group than in the virus group. Overall, these results are important in understanding the cell localization of TSHSV and the immune response of infected turtles.