Two Mx genes identified in European sea bass (Dicentrarchus labrax) respond differently to VNNV infection

The European sea bass (Dicentrarchus labrax) is an important farmed fish species in the Mediterranean area, very sensitive to the infection by encephalopathy and retinopathy virus (VERv), or Betanodavirus, which causes massive mortalities. Effective vaccines to fight the pathology are not yet available and in this work we describe a promising intraperitoneal immunization route against VERv of sea bass juveniles. We performed intraperitoneal and immersion immunization trials with a VERv (isolate 283.2009 RGNNV) inactivated by formalin, β-propiolactone and heat treatment. Interestingly, the intraperitoneal immunization with formalin-inactivated VERv induced a significant antigen-specific IgM production, differently from other inactivation protocols. However, the same formalin-inactivated antigen resulted in very low IgM antibodies when administered by immersion. Following the intraperitoneal injection with formalin-inactivated virus, the quantitative expression of the antiviral MxA gene showed a modulation of transcripts in the gut after 48 h and on head kidney after 24 h, whereas ISG12 gene was significantly up-regulated after 48 h on both tissues. In immersion immunization with formalin-inactivated VERv, a modulation of MxA and ISG12 genes after 24 h post-treatment was detected in the gills. An effective uptake of VERv particles in the gills was confirmed by immunohistochemistry using anti-VERv antibodies. Lastly, in challenge experiments using live VERv after intraperitoneal immunization with formalin-inactivated VERv, we observed a significant increase (81.9%) in relative survival percentage with respect to non-immunized fish, whereas immersion immunization resulted in no protection. Our results suggest that intraperitoneal immunization with formalin-inactivated VERv could be a safe and effective strategy to fight Betanodavirus infection in European sea bass.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-016-0376-3) contains supplementary material, which is available to authorized users.

Section: Discussionmentioning

confidence: 99%

A formalin-inactivated immunogen against viral encephalopathy and retinopathy (VER) disease in European sea bass (Dicentrarchus labrax): immunological and protection effects

Nuñez-Ortiz

Pascoli

Picchietti

et al. 2016

“…To our knowledge, this work is the first report of Mx transcription induced by SJNNV in head kidney from European sea bass, whereas previous reports have described Mx transcription in this fish species following RGNNV infection. Scapigliati et al [ 28 ] and Novel et al [ 39 ] recorded early Mx transcription (6 hpi); however, Chaves-Pozo et al [ 27 ] did not detect Mx mRNA before 24 hpi. Differences in fish age, viral isolates, and methodology may explain these discrepancies.…”

Section: Discussionmentioning

confidence: 99%

SJNNV down-regulates RGNNV replication in European sea bass by the induction of the type I interferon system

Carballo

García-Rosado

Borrego

et al. 2016

European sea bass is highly susceptible to the betanodavirus RGNNV genotype, although the SJNNV genotype has also been detected in this fish species. The coexistence of both genotypes may affect the replication of both viruses by viral interaction or by stimulation of the host antiviral defense system in which the IFN I system plays a key role. IFN I triggers the transcription of interferon-stimulated genes, including Mx genes, whose expression has been used as a reporter of IFN I activity. The present study evaluated the effect of a primary exposure to an SJNNV isolate on a subsequent RGNNV infection and analyzed the role of the IFN I system in controlling VNNV infections in sea bass using different in vivo approaches. VNNV infection and Mx transcription were comparatively evaluated after single infections, superinfection (SJ+RG) and co-infection (poly I:C+RG). The single RGNNV infection resulted in a 24% survival rate, whereas the previous SJNNV or poly I:C inoculation increased the survival rate up to 96 and 100%, respectively. RGNNV replication in superinfection was reduced compared with RGNNV replication after a single inoculation. Mx transcription analysis shows differential induction of the IFN I system by both isolates. SJNNV was a potent Mx inducer, whereas RGNNV induced lower Mx transcription and did not interfere with the IFN I system triggered by SJNNV or poly I:C. This study demonstrates that an antiviral state exists after SJNNV and poly I:C injection, suggesting that the IFN I system plays an important role against VNNV infections in sea bass.

“…The in vivo effect of NNV has also been analysed by RNA-Seq in the brain of sevenband grouper [10], pooled brain/eye and head kidney samples from Senegalese sole [11], the brain of Malabar grouper [12], and the liver, spleen and kidney of Epinephelus moara [13]. However, the in vivo response of European sea bass remains almost completely unexplored, and only a small number of publications have reported the modulation or involvement of immune factors in different tissues of D. labrax infected with NNV [14][15][16][17][18][19][20][21][22]. Therefore, the aim of this work was to analyse the complete transcriptome response of European sea bass to nodavirus infection.…”

Section: Introductionmentioning

confidence: 99%

RNA-Seq analysis of European sea bass (Dicentrarchus labrax L.) infected with nodavirus reveals powerful modulation of the stress response

Lama

Pereiro

Valenzuela-Muñoz

et al. 2020

Nodavirus, or nervous necrosis virus (NNV), is the causative agent of viral encephalopathy and retinopathy (VER), a severe disease affecting numerous fish species worldwide. European sea bass, a cultured species of great economic importance, is highly susceptible to the disease. To better understand the response of this organism to NNV, we conducted RNA-Seq analysis of the brain and head kidney from experimentally infected and uninfected sea bass juveniles at 24 and 72 hours post-infection (hpi). Contrary to what was expected, we observed modest modulation of immune-related genes in the brain, the target organ of this virus, and some of these genes were even downregulated. However, genes involved in the stress response showed extremely high modulation. Accordingly, the genes encoding the enzymes implicated in the synthesis of cortisol were almost the only overexpressed genes in the head kidney at 24 hpi. This stress response was attenuated after 72 h in both tissues, and a progressive immune response against the virus was mounted. Moreover, experiments were conducted to determine how stress activation could impact NNV replication. Our results show the complex interplay between viral activity, the stress reaction and the immune response.