Establishment and characterization of a new cell line (SSP-9) derived from Atlantic salmon Salmo salar that expresses type I ifn

In the present work, the establishment and biological characterization of a new cell line, SSP-9, derived from the pronephros of the Atlantic salmon Salmo salar, are reported. These cells grew well in Leibovitz's (L15) medium supplemented with 10% foetal calf serum at temperatures from 15 to 25° C, and they have been sub-cultured over 100 passages to produce a continuous cell line with an epithelial-like morphology. The SSP-9 cells attached and spread efficiently at different plating densities, retaining 80% of cell viability after storage in liquid nitrogen. When karyotyped, the cells had 40-52 chromosomes, with a modal number of 48. Viral susceptibility tests showed that SSP-9 cells were susceptible to infectious pancreatic necrosis virus and infectious haematopoietic necrosis virus, producing infectious virus and regular cytopathic effects. Moreover, these cells could be stimulated by poly I:C, showing significant up-regulation in the expression of the genes that regulate immune responses, such as ifn and mx-1. SSP-9 cells constitutively express genes characteristic of macrophages, such as major histocompatibility complex (mhc-II) and interleukin 12b (il-12b), and flow cytometry assays confirmed that SSP-9 cells can be permanently transfected with plasmids expressing a reporter gene. Accordingly, this new cell line is apparently suitable for transgenic manipulation, and to study host cell-virus interactions and immune processes.

Immune responses elicited in rainbow trout through the administration of infectious pancreatic necrosis virus-like particles

Virus like particles (VLPs) against viral pathogens not only constitute a novel approach for the development of antiviral vaccines for an specific virus, but also for the creation of multivalent vaccines in which antigens from other pathogens may be expressed on the surface of these VLPs. Despite positive results on protection for many of these VLPs in both fish and mammals, not many studies have focused on the immune response triggered by these particles; studies that may provide hints for the identification of immune mechanisms responsible for antiviral protection, which are mostly unknown in fish. In the current work, we have studied the levels of transcription of several immune genes in the spleen of rainbow trout (Oncorhynchus mykiss) intraperitoneally injected with VLPs from infectious pancreatic necrosis virus (IPNV) focusing on the chemokine response as well as the response of genes related to interferon (IFN) production. Surprisingly, the capacity of VLPs to induce chemokines differed from that of live IPNV, suggesting a direct effect of viral replication on the chemokine response in this organ. While VLPs up-regulated the transcription of CK3, CK10 and CXCd and down-modulated CK5B, CK6 and CK9 transcription, a previous study in which the transcription of γIP, CXCd, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12 had been studied demonstrated that IPNV only significantly up-regulated CK6 and down-modulated CK3 in the spleen. On the other hand, the administration of VLPs produced a strong mobilization to the peritoneum of CD4(+), IgM(+), IgT(+) and CD83(+) leukocytes similar to that induced by the live viral infection. In both cases, this leukocyte recruitment seemed to be greatly mediated through CK3, CK5B, CK9 and CK10 chemokine production. These results together with the fact that VLPs strongly induced non-specific lymphocyte proliferation and specific anti-IPNV antibody production point to VLPs as excellent candidates for vaccine development.

Detection of lymphocystis disease virus (LCDV) in asymptomatic cultured gilt-head seabream (Sparus aurata, L.) using an immunoblot technique

An immunoblot technique for the detection of lymphocystis disease virus (LCDV) in naturally infected gilt-head seabream (Sparus aurata, L.) has been developed. A specific antiserum against a 60 kDa viral protein has been proven to be an appropriate tool for LCDV diagnosis either from inoculated cell cultures or from fish tissues using the immunoblot assay. The sensitivity of this technique varied between 10(-1) and 10(2) TCID50. LCDV has also been detected in fish tissues from both, diseased and asymptomatic gilt-head seabream. For the asymptomatic fish detection, a viral amplification step in cell culture and a subsequent viral concentration using polyethylene glycol (PEG) (600 wt) are required. On the contrary, immunoblot allowed the detection of LCDV antigens directly from tissue homogenates of diseased fish. The method described in this study shows higher sensitivity than classical detection techniques based on cell culture inoculation.

Comparative evaluation of five serological methods and RT-PCR assay for the detection of IPNV in fish

In the present study, six diagnostic methods for the detection of infectious pancreatic necrosis virus (IPNV) (indirect immunofluorescence, flow cytometry, immunoperoxidase, immunodot blot, immunostaphylococcus-protein A, and RT-PCR) have been comparatively evaluated using the seroneutralization as the reference assay, and 83 Spanish isolates and 3 reference strains. The most reliable methods were flow cytometry and RT-PCR which could detect virus at titers of 1x10(2) and 1x10(3) TCID50/ml, respectively. At a multiplicity of infection of 50, both assays allowed the earliest detection of IPNV at 4 h post-inoculation. Indirect immunofluorescence and immunoperoxidase assays required at least 6 h post-inoculation to detect viral antigens. The immunodot blot assay possesses low sensitivity and the immunostaphylococcus-protein A test cannot be applied for routine examination of IPNV. Positive reactions were obtained in 100% of the samples tested by seroneutralization and RT-PCR, 90.4% by the flow cytometry, 80.7% by the indirect immunofluorescence assay, 67.5% by the immunoperoxidase, 62.6% by the immunodot blot, and only 27.7% by immunostaphylococcus-protein A test. Therefore, RT-PCR and flow cytometry were the most appropriate and sensitive methods for the routine detection of IPNV from affected fish.