VACCINATION of Atlantic salmon leads to long-lasting higher levels of serum immunoglobulin and possible skewed ratios of two distinct IgM isotypes

Abstract

<p style="text-align:justify;"> <span style="font-size:10.0pt;"><span style="font-family:Verdana;font-size:12px;">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 (</span><i><span style="font-family:Verdana;font-size:12px;">Salmosalar</span></i><span style="font-family:Verdana;font-size:12px;">) 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 (</span><i><span style="font-family:Verdana;font-size:12px;">Onchorhynchusmykiss</span></i><span style="font-family:Verdana;font-size:12px;">), showing that </span></span><span style="font-size:12px;line-height:1.5;font-family:Verdana;">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 sinc</span><span style="font-size:12px;line-height:1.5;font-family:Verdana;">e tools are available to distinguish IgM-A and IgM- </span><span style="font-size:12px;line-height:1.5;font-family:Verdana;">B in this species.</span> </p

Immunoglobulin Isotypes in Atlantic Salmon, Salmo Salar

“…The μA and μB genes correspond to two distinct IgM subpopulations in Atlantic salmon (IgM-A and IgM-B), which can be isolated from serum by gel filtration followed by anion exchange chromatography [ 31 , 32 , 33 , 34 , 35 ]. The IgM-B:IgM-A ratio in serum is typically 60:40, but skewed ratios are also observed [ 36 ]. An IgM-B:IgM-A ratio of 60:40 was found to be in accordance with the relative amounts of lymphocytes displaying IgM-B versus IgM-A on the surface [ 37 ].…”

“…In some recent reports it has been shown that Atlantic salmon that have received commercial oil-adjuvanted vaccines have IgM concentrations that are two- to fourfold higher than in un-vaccinated fish. The depot effect of the mineral oil seems to trigger a continuous higher production of IgM which persists to the fish are slaughtered [ 36 , 52 ]. As shown in Table 1 , a study of rainbow trout revealed an average serum IgM concentration of 3.3 mg/mL in free living fish [ 48 ].…”