Common carp type I interferon responses and its influence on the resistance of carp genetic lines to virus infection
Final Report Abstract
The objective of the project was to address virus induced fish losses in carp aquaculture by investigating the significance of interferon (IFN) responses for the resistance of carp to viral diseases. The main hypothesis for the project was, that differences in type I IFN responses could have an impact on virus replication and disease outcome, both in individuals and populations. For testing this hypothesis, individuals from genetically different carp lines were infected with the carp pathogenic viruses carp edema virus (CEV), a newly described poxvirus, cyprinid herpesvirus 3 (CyHV-3, also known as koi herpesvirus), a member of the Alloherpesviridae, and spring viremia of carp virus (SVCV), a member of Rhabdoviridae. In addition, the induction of IFN responses of carp cells to infection with these viruses were analysed in vitro. Infections with all three viruses developed considerably differently in the infected carp lines Amur wild carp (AS), Ropsha carp (ROP), Prerov scaly carp (PS) and koi. Koi were most susceptible to infections with CEV and CyHV-3 and experienced high virus loads associated with high losses, while AS and ROP carp were remarkably resistant to infections with these viruses. PS carp were most susceptible to SVCV-infection. The infection with the different viruses induced IFN responses to a different extent. While in carp under SVCV-infection the interferon pathway was strongly upregulated, this pathway was only marginally upregulated in carp under CEV or CyHV-3 infection. In all infections, the upregulation of IFN responses could not be correlated to the resistance of carp to the infection, but carp from the more susceptible genetic lines developed a higher IFN response, together with a higher virus load, than carp with higher resistance to the infection. Hence, in contrast to the working hypothesis, the resistance of carp to the virus infections could not be related to antiviral IFN responses. Subsequent in vitro studies showed the ability of CyHV-3 for manipulating cellular IFN responses. In cells under CyHV-3 infection, significantly lower IFN responses could be observed when these cells were also stimulated with ligands to cytosolic sensors of foreign double stranded DNA than in stimulated but not infected cells. Since interferon-stimulated proteins largely alter the cell metabolism and by this hamper virus infection or replication, we analysed whether CyHV-3 is vulnerable to IFN induced changes of the cell metabolism. The entry of CyHV-3 into host cells relies on the presence of cholesterol in the cell membrane. The suppression of cholesterol synthesis is an important antiviral mechanism of type I IFNs, and our studies could confirm the alteration of cholesterol metabolism by IFN responses in carp cells as well. Subsequently, we could confirm that the entry of CyHV-3 into cells was stunted in cells with suppressed cholesterol synthesis, or when the proportion of the antiviral oxysterol 25 hydroxycholesterol in the cell membrane was increased. This confirms that in particular IFN induced alterations of the sterol metabolisms might hamper the development of CyHV-3. Further high throughput sequencing of mRNA transcripts from the head kidney of CyHV-3-infected and non-infected carp from the susceptible (koi) and the resistant (RPO) genetic lines suggest a wide manipulation of innate and adaptive immune responses in carp from the susceptible line under CyHV-3 infection. This would explain the rapid development of the virus and a high susceptibility to CyHV-3 mediated disease in these fish. The infection experiments performed in this project provide excellent models for an analysis of the genetic basis for resistance to virus infections carp. These findings can also support efforts of breeding programs with resistant carp lines to protect carp aquaculture from losses caused by the viruses under study. Surprisingly, no indication could be found for an involvement of the IFN response in the resistance to virus infection. We could conform, that CyHV-3 has the ability to manipulate immune responses of carp, and, in particular the antiviral IFN response. Our data form a good starting point for a closer analysis of the interplay of CyHV-3 and cellular IFN response, employing virus mutants recently developed by other scientists.
Publications
- (2017) Experimental infections of different carp strains with the carp edema virus (CEV) give insight into the infection biology of the virus and indicate possible solutions to problems caused by koi sleepy disease (KSD) in aquaculture. Veterinary Research 48:12
Adamek M, Oschilewski A, Wohlsein P, Jung-Schroers V, Teitge F, Dawson A, Glea D, Piackova V, Kocour M, Adamek J, Bergmann SM, Steinhagen D
(See online at https://doi.org/10.1186/s13567-017-0416-7) - (2017) Viral infection in common carp leads to a disturbance of mucin expression in mucosal tissues. Fish & Shellfish Immunology 71, 353-358
Adamek M, Hazerli D, Matras M, Teitge F, Reichert M, Steinhagen D
(See online at https://doi.org/10.1016/j.fsi.2017.10.029) - (2018) Quantification of sterols from carp cell lines using HPLC-MS. Sep Sci plus 1, 11-21
Beck A, Jordan LK, Herlitze S, Amtmann A, Christian J, Brogden G, Adamek M, Naim HY, Becker AM
(See online at https://doi.org/10.1002/sscp.201700021)
