Antibody response after immunization as a potentialindirect marker for improved resistance against furunculosis

Different humoral immune parameters were evaluated as possible indirect markers for breeding for improved resistance against furunculosis, using family material consisting of 30 groups of full-siblings of Atlantic salmon (Salmo salar). Other fish from the same groups of full-siblings had previously been challenged with Aeromonas salmonicida, and survival rates had been recorded. The immune parameters included the level of antibodies against A-layer protein and lipolpolysaccharide (LPS) from A. salmonicida, before and after immunization and the total level of immunoglobin M (IgM), after immunization. Significant full-sibling variation in the three immune parameters, recorded after immunization was found, indicating possible genetic variation in these traits. A significant negative correlation (r= − 0·41, P=0·02) was found between the least square means for the level of total IgM for the groups of full-siblings, and the survival rates for the corresponding groups of full-siblings in the previous challenge test with A. salmonicida. In a stepwise multiple regression model, with survival rates as the dependent variable, and the total set of immune parameters as the explanatory variables, the effects of both the total level of IgM and the level of antibodies against the A-layer protein after immunization were significant. In contrast to the total level of IgM, the level of anti-A-protein antibodies was positively correlated to the survival rates, in the multiple regression model. While the total level of IgM alone explained 17% (r2=0·17) of the survival rates, the two parameters together explained 37% (r2=0·37) of the survival rates in the model. These two immune parameters, when used together, therefore seem to be possible indirect markers when breeding for improved resistance against furunculosis.