Isolation and partial characterization of serum immunoglobulins from sea bass (Dicentrarchus labraxL.) and gilthead sea bream (Sparus aurataL.)

Serum immunoglobulins from sea bass and sea bream were purified using affinity chromatography methods. Fish were immunized with purified goat IgG, and the specific fish antibodies purified from the immune serum on a goat IgG-mmobilized agarose gel. Native molecular weights of the immunoglobulins were determined by size sieving chromatography as 855 000 Da for sea bass, and 830 000 Da for gilthead sea bream. Analysis of the immunoglobulins by reducing SDS-PAGE showed them to be composed of a single μ-like heavy chain, weighing about 78 kDa forD. labraxand 75 kDa forS. aurata. Certain differences were found for the light chains, which were resolved as two (27·5 and 28·5 kDa) polypeptides inD. labraxsamples, and three (27, 28 and 29 kDa) bands inS. aurata. Rabbit polyclonal antisera against both immunoglobulins were produced and tested by ELISA and immunoblotting techniques. The antisera reacted mainly with the high molecular weight chain of the immunoglobulins at high dilutions. Both immunoglobulins are similar tetrameric forms, but differences in the molecular weight of their constituent chains suggest some structural heterogeneity.