Molecular characterization and expression analysis of three subclasses of IgT in rainbow trout (Oncorhynchus mykiss)

Abstract

As the teleost specific immunoglobulin, IgT plays important roles in systemic and mucosal immunity. In the current study, in rainbow trout, we have cloned the heavy chain (Igτ) genes of a secretory form of IgT2 as well as the membrane and secretory forms of a third IgT subclass, termed IgT3. Conserved cysteine and tryptophan residues that are crucial for the folding of the immunoglobulin domain as well as hydrophobic and hydrophilic residues within CART motif were identified in all IgT subclasses. Through analysis of the rainbow trout genome assembly, Igτ3 gene was found localized upstream of Igτ1 gene, while Igτ2 gene situated on another scaffold. At the transcriptional level, Igτ1 was mainly expressed in both systemic and mucosal lymphoid tissues, while Igτ2 was largely expressed in systemic lymphoid organs. After LPS and poly (I:C) treatment, Igτ1 and Igτ2 genes exhibited different expression profiles. Interestingly the transcriptional level of Igτ3 was negligible, although its protein product could be identified in trout serum. Importantly, a previously reported monoclonal antibody directed against trout IgT1 was able to recognize IgT2 and IgT3. These data demonstrate that there exist three subclasses of IgT in rainbow trout, and that their heavy chain genes display different expression patterns during stimulation. Overall, our data reflect the diversity and complexity of immunoglobulin in trout, thus provide a better understanding of the IgT system in the immune response of teleost fish.

A BCWD-resistant line of rainbow trout exhibits higher abundance of IgT+ B cells and heavy chain tau transcripts compared to a susceptible line following challenge with Flavobacterium psychrophilum

“…The answer likely lies within the large and complex structure of the rainbow trout Ig HC locus: HCtau gene segments are encoded within the HCmu/delta loci, in a nested gene structure (Hansen et al, 2005) (Zhang et al, 2017). Dτ and Jτ segments are located between (isotype-shared) VH segments (at the 5′ end of the Ig HC gene), and the Cτ1 segment is located immediately downstream from the Dτ1 and Jτ1 segments.…”

“…The monoclonal mouse anti-trout immunoglobulin tau antibody (41.8; (Zhang et al, 2010) recognizes IgT1, IgT2, and IgT3 (Zhang et al, 2017) and was a gift from Dr. Oriol Sunyer. The rabbit polyclonal Pax5.PD antibody (previously called ED-1; (Zwollo et al, 2008)) recognizes the paired domain of vertebrate Pax5 and detects trout Pax5 in pre-B through plasmablast stages (McMurray et al, 2013).…”

“…A total of three igt genes has been described in the rainbow trout, including igt1, igt2 and igt3, encoding IgT1, IgT2, and IgT3 (Zhang et al, 2017). Each of these genes has a different expression pattern.…”

“…Each of these genes has a different expression pattern. igt1 was found to be expressed both in systemic and mucosal tissues, with highest expression in blood and spleen, followed by anterior kidney and gut; igt2 was expressed mostly in systemic tissues, with highest expression levels in thymus and blood, but virtually absent from anterior kidney, gut and skin; igt3 levels were undetectable by PCR except in spleen, but IgT3 Ig could be detected in serum (Zhang et al, 2017). In vivo challenge with LPS, but not poly(I:C) resulted in upregulation of igt1 and igt2 in gut, but effects on the spleen were minor.…”

“…In vivo challenge with LPS, but not poly(I:C) resulted in upregulation of igt1 and igt2 in gut, but effects on the spleen were minor. A monoclonal antibody has been generated (Zhang et al, 2010) that recognizes all three isotypes of IgT (Zhang et al 2017). A few gene-expression studies have reported on the roles of IgT in response to bacterial pathogens in recent years.…”