Serum Immunoglobulin M (IgM) in Sakhalin Taimen (Hucho perryi): Purification, Characterization, Circulating Levels, and Specific IgM Production by the Parasitic Salmincola stellatus

Immunoglobulin M (IgM) was purified from the serum of Sakhalin taimen (Hucho perryi) by salting-out, ion-exchange chromatography on DEAE-cellulose, and gel filtration on Sepharose 6B. The intact, tetrameric taimen IgM has a mass of 750 kDa with molecular architecture typical of IgM from other salmonids. The molecular weights of heavy (μ) chain and light chains (L) of the IgM monomer were estimated to be 68 kDa and 23 kDa, respectively. Purified taimen IgM was used to raise a specific rabbit antiserum and to develop a single radial immunodiffusion assay for measuring circulating IgM levels. The serum IgM levels in captive, immature or maturing female taimen varied between 1 and 5 mg/ml, showing seasonal changes regardless of fish age, with relatively low levels in spring and conversely high levels in autumn. Production of specific serum IgM to a parasite, Salmincola stellatus, was assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The parasitized taimen serum could react with protein components of aqueous extracts from the parasite that were blotted on a nitrocellulose membrane after SDS-PAGE, but normal taimen serum did not, indicating that the parasitized fish produced the specific IgM to S. stellatus in the serum.