Innate immunity plays a key role against the nervous necrosis virus (NNV) before adaptive immunity kicks off during fish development. We have studied the interferon-inducible Mx and the antimicrobial peptide hepcidin genes to probe the status of innate immunity in red-spotted grouper, Epinephelus akaara larvae and juveniles. For this study we examined the NNV infections in the farmed E. akaara, to generate the complete coding sequences of Mx and hepcidin, and to characterize the expression during development. Red-spotted grouper NNV (RGNNV) was mainly detected in the brain, gills and heart of the sick groupers, and the larvae from 0 to 23. day-post hatching (dph) of the farmed asymptomatic groupers were detected RGNNV-positive using real-time PCR (RT-PCR). The open reading frame (ORF) of E. akaara Mx gene is 1878. bp long encoding a putative protein of 626 amino acids, while the ORF of hepcidin is 258. bp in length encoding 86 amino acid residues. An RT-PCR was optimized to estimate the expression patterns of Mx and hepcidin in E. akaara. Mx was constitutively expressed in head kidney, liver, spleen, heart, gills, muscle, brain, thymus and intestine, and it was first detected on 2. dph and increased to a higher level after 15. dph. Hepcidin was mainly expressed in the liver and intestine, and it was detected in the fertilized-egg showing and significantly increased expression after 29. dph. It could be hypothesized that the farmed groupers are RGNNV carriers, promoting vertical virus transmission from parents to the offspring, as the eggs were tested RGNNV positive. We can conclude that there should be a balance between the innate immunity and the RGNNV infection during early development, and RGNNV will outbreak when the innate immunity becomes weak and adaptive immunity is still immature. © 2013 Elsevier B.V.
|Publication status||Published - 5 Sep 2013|
- Epinephelus akaara
- Innate immunity
- Nervous necrosis virus