Alterations in total protein, IgM and specific antibody activity of male and female sea bass (Dicentrarchus labraxL., 1758) sera following injection with killedVibrio anguillarum

Abstract

The relationship between the levels of total proteins, immunoglobulins and antibody activity in serum of sea bass broodstock, following one or two intraperitoneal injections of heat-killedVibrio anguillarum(V1), was studied over a period of 10 months. Determination of immunoglobulin (IgM) level was carried out using a double monoclonal antibody sandwich ELISA and the specific antibody activity to V1 (AbV1) quantified by indirect ELISA. IgM level decreased during the first month post-immunisation (p.i.), but persisted at a high level from the third month until the eighth month p.i. in injected fish and until the tenth month p.i. in boosted fish. AbV1 level increased after 2 weeks and remained elevated for longer than 10 months p.i. Neither the IgM nor the AbV1 levels of control fish were changed following an injection of phosphate-buffered saline. The V1 injection did not modify the protein level, but alteration of protein levels over time differed between males and females. Moreover IgM production was significantly higher, but no significant difference was found between males and females in AbV1 production. The decrease of IgM level after injection may be explained by consumption of IgM, with paratopes close to the injected antigen epitope, which are mobilised to compensate for the lack of the specific antibodies. This early decrease is likely to be an adaptation rather than a deficiency of the immune system.