The recall of antigen-specific antibody-secreting cells in Solea senegalensis gives clues on the secondary immune response in flatfish.

Abstract

In this study, monoclonal antibodies (mAbs) specific for sole immunoglobulin M (IgM) were generated, which allowed us to evaluate the kinetics of IgM+ B cell responses, assess the recruitment of these cells to the peritoneum following vaccination, and compare the dynamics of antigen-specific antibody-secreting cells in the spleen and kidney of primed and boosted fish. Solea senegalensis is a commercially important species in aquaculture, and the development of vaccines is of great interest. Currently, autogenous vaccines provide partial protection against furunculosis, but their efficacy remains limited. We evaluated the efficacy of 2 vaccines formulated with whole (STV-W) or particulated bacterin from an atypical Aeromonas salmonicida strain. The vaccines provided moderate short-term protection (48% relative percent survival for STV-W), which included activation of proinflammatory genes, cell mobilization to the injection site, and generation of specific antibodies. However, this protection did not persist beyond 3 mo without booster. To further investigate the response, mAbs specific to sole immunoglobulin were produced. Two of these mAbs, which recognize the IgM heavy chain, successfully labeled a population of IgM+ cells from spleen and kidney leukocytes analyzed by flow cytometry. Fluorescence-activated cell sorting-sorted IgM+ cells exhibited strong IgM gene expression. Interestingly, a booster administered to previously vaccinated and surviving fish 10 mo postchallenge led to activation of antibody-secreting cells and a more rapid production of specific IgM antibodies compared with primed fish. This indicates that sole are capable of mounting a secondary immune response upon re-exposure. Overall, these findings provide valuable insights into the mechanisms of vaccine-induced protection in fish.