The primary and secondary antibody responses to IROMP antigens in Atlantic salmon (Salmo salarL) immunised with A+and A−Aeromonas salmonicidabacterins

The aim of this work was to investigate if the presence of Aeromonas salmonicida A-layer had a suppressive effect on the development of antibodies in Atlantic salmon to outer membrane protein antigens expressed when A. salmonicida is grown under iron-restricting conditions. Atlantic salmon were immunised with an A-layer positive (A + ) or A-layer negative (A − ) A. salmonicida iron-restricted whole cell bacterin, and were boosted 8 weeks later with homologous bacterin, heterologous bacterin, or phosphate buffered saline. Serum antibody titres to iron-restricted outer membrane protein antigens were measured for a period of 8 months. It was found that the presence of A-layer at the time of priming, or the introduction of A-layer 8 weeks post-prime, had no significant effect on the development of antibody responses to iron-restricted outer membrane protein antigens. In addition, it was found that boosting fish when antibody levels are high gave an enhanced antibody response compared to unboosted fish, and this response was characterised by both an increase in specific antibody titres and an increase in the percentage of responding fish.