Immunoglobulin T from sea bass (Dicentrarchus labrax L.): molecular characterization, tissue localization and expression after nodavirus infection

Abstract

BackgroundImmunoglobulins (Igs) are fundamental components of the adaptive immune system of vertebrates, with the IgT/IgZ isotype specific of Teleosts. In this paper we describe the identification of an IgT heavy chain from the European sea bass (Dicentrarchus labrax L.), its molecular characterization and tissue mRNA localization by in situ hybridization.ResultsSea bass IgT consists of 552 aa (Accession Number KM410929) and it contains a putative 19 amino acids long signal peptide and one potential N-glycosylation site. The C-region consists of four CH domains; each contains the cysteine and tryptophan residues required for their correct folding. Based on the recent sequencing of sea bass genome, we have identified five different genomic contigs bearing exons unequivocally pertaining to IgT (CH2, CH3 and CH4), but none corresponded to a complete IgH locus as IgT sequences were found in the highly fragmented assembled genomic regions which could not be assigned to any major scaffold. The 3D structure of sea bass IgT has been modelled using the crystal structure of a mouse Ig gamma as a template, thus showing that the amino acid sequence is suitable for the expected topology referred to an immunoglobulin-like architecture. The basal expression of sea bass IgT and IgM in different organs has been analysed: gut and gills, important mucosal organs, showed high IgT transcripts levels and this was the first indication of the possible involvement of sea bass IgT in mucosal immune responses. Moreover, sea bass IgT expression increased in gills and spleen after infection with nodavirus, highlighting the importance of IgT in sea bass immune responses. In situ hybridization confirmed the presence of IgT transcripts in the gut and it revealed a differential expression along the intestinal tract, with a major expression in the posterior intestine, suggesting the hindgut as a site for the recruitment of IgT+ cells in this species. IgT transcripts were also found in gill filaments and parallel lamellae and, for the first time, we identified scattered IgT positive cells in the liver, with a strong signal in the hepatic parenchyma.ConclusionsIn conclusion, we performed a full molecular characterization of IgT in sea bass that points out its possible involvement in mucosal immune responses of this species.

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

“…Here, we sought to study the response of D. labrax to infection by NNV, one of the most threatening pathogens in the culture of this important commercial fish species. Some previous studies have revealed the overexpression of certain immune genes after in vivo or in vitro infection with NNV in both European sea bass [14][15][16][17][18][19][20][21][22] and other fish species [5, 6, 8, 10-13, 20, 34], but the present study is the first to conduct RNA-Seq in D. labrax after in vivo infection with NNV.…”

“…It has been previously suggested that the adaptive immune response is critical in the defence against NNV, even at early times post-infection [22,[43][44][45]. Considering this suggestion and the observed overexpression of the genes involved in cortisol synthesis in the head kidney, we further investigated whether cortisol overload increases the susceptibility of European sea bass to NNV.…”

“…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.…”

Advances in the study of nodavirus

“…Besides innate and cell mediated immunity, humoral immunity also plays an important role in protecting fish against nodavirus infection ( Chen et al, 2014 ), especially the two immunoglobulins, IgM and IgT. Infection of susceptible seabass with low titer of nodavirus did not significantly alter the expression of IgM and IgT in the gills and spleen ( Buonocore et al, 2017 ) but only induced a marginal increase of serum IgM ( Scapigliati et al, 2010 ). On the other hand, activation of IgM + and IgT + B cells in the brain and overexpression of soluble IgT + by B cells in the head kidney by early inflammatory response in the central nervous system reduced nodaviral replication in the resistant aquaculture-relevant fish species ( Lopez-Munoz et al, 2012 ; Piazzon et al, 2016 ).…”

Peer Review #2 of "Advances in the study of nodavirus (v0.2)"

“…Manuscript to be reviewed immunoglobulins, IgM and IgT. Infection of susceptible seabass with low titer of nodavirus did not significantly alter the expression of IgM and IgT in the gills and spleen (Buonocore et al, 2017) but only induced a marginal increase of serum IgM (Scapigliati et al, 2010). On the other hand, activation of IgM + and IgT + B cells in the brain and overexpression of soluble IgT + by B cells in the head kidney by early inflammatory response in the central nervous system reduced nodaviral replication in the resistant aquaculture-relevant fish species (Lopez-Munoz, 2012;Piazzon et al, 2016).…”