TITLE:
VACCINATION of Atlantic salmon leads to long-lasting higher levels of serum immunoglobulin and possible skewed ratios of two distinct IgM isotypes
AUTHORS:
Atif Kamil, Per Gunnar Fjelldal, Tom Hansen, Arnt Raae, Erling Olaf Koppang, Ivar Hordvik
KEYWORDS:
Teleost; Atlantic Salmon; Vaccine; IgM; Tetraploidy
JOURNAL NAME:
Advances in Bioscience and Biotechnology,
Vol.4 No.4A,
April
30,
2013
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.