Abstract
Primary and secondary antibody responses in blood of teleost fish are mainly IgM mediated, as they lack an IgG homolog and a class switch mechanism. Thus, the major serum immunoglobulin is tetrameric IgM. A unique antibody class in teleosts; named IgT, appears to be specialized for mucosal immunity and is present in low concentrations in serum. A third class; IgD was recently detected in serum of rainbow trout, but is less abundant than IgT. In the present study, relative quantification of total IgM showed that Atlantic salmon (Salmosalar) which had received an oil-adjuvanted commercial vaccine maintained about 2-fold higher levels of IgM; 14 and 17 months after intraperitoneal injection, in comparison to unvaccinated fish kept in the same cage. Similar results were obtained by ELISA (serum IgM) and reverse transcription real time PCR (spleen mRNA). Analyses conducted in our lab have shown that several salmonid species possess two slightly different IgM isotypes as a result of ancestral tetraploidy. In Atlantic salmon, two distinct IgM subpopulations (A and B) can be separated by anion exchange chromatography. The IgM-B tetramer exhibits a higher degree of disulfide cross-linking than IgM-A, presumably due to an extra cysteine near the C-terminus of the heavy chain. The typical A/B ratio is approximately 40/60. Anion exchange elution profiles of serum IgM from vaccinated fish indicate that prolonged triggering of the immune system can lead to a skewed ratio of IgM-A/IgM-B. In the context of recent results from rainbow trout (Onchorhynchusmykiss), showing that high affinity antibodies are more highly polymerized and have a longer half life time, Atlantic salmon is an interesting model to elucidate these aspects further since tools are available to distinguish IgM-A and IgM- B in this species.
Highlights
The major form of serum immunoglobulin in teleost fish is IgM, whereas two other classes of antibodies; IgT and IgD, are present in relatively low quantities [1]
Relative quantification of total IgM showed that Atlantic salmon (Salmo salar) which had received an oiladjuvanted commercial vaccine maintained about 2-fold higher levels of IgM; 14 and 17 months after intraperitoneal injection, in comparison to unvaccinated fish kept in the same cage
The plasma concentration of IgT was estimated to be 1000 fold lower than IgM in naïve fish [2].Transcripts encoding membrane bound IgD seem to be dominant in most teleosts, but recently it was shown that alternative mRNA usage generates a secreted form of IgD in rainbow trout [3]
Summary
The major form of serum immunoglobulin in teleost fish is IgM, whereas two other classes of antibodies; IgT and IgD, are present in relatively low quantities [1]. The plasma concentration of IgT was estimated to be 1000 fold lower than IgM in naïve fish [2].Transcripts encoding membrane bound IgD seem to be dominant in most teleosts, but recently it was shown that alternative mRNA usage generates a secreted form of IgD in rainbow trout [3]. A separate gene encodes secretory IgD, but this is not typical for teleost fish [4]. Teleosts constitute a heterogenous group of vertebrates with several examples of unique Ig structures, gene duplications and splicing variants [1,5,6,7,8]. In contrast to higher vertebrates, the expression of Ig isotypes in teleost fish is not regulated by a class switch mechanism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
