Inactivated Aeromonas salmonicida impairs adaptive immunity in lumpfish (Cyclopterus lumpus)

Abstract

AbstractAeromonas salmonicida, a widely distributed aquatic pathogen causing furunculosis in fish, exhibits varied virulence, posing challenges in infectious disease and immunity studies, notably in vaccine efficacy assessment. Lumpfish (Cyclopterus lumpus) has become a valuable model for marine pathogenesis studies. This study evaluated several antigen preparations against A. salmonicida J223, a hypervirulent strain of teleost fish, including lumpfish. The potential immune protective effect of A. salmonicida bacterins in the presence and absence of the A‐layer and extracellular products was tested in lumpfish. Also, we evaluated the impact of A. salmonicida outer membrane proteins (OMPs) and iron‐regulated outer membrane proteins (IROMPs) on lumpfish immunity. The immunized lumpfish were intraperitoneally (i.p.) challenged with 104 A. salmonicida cells/dose at 8 weeks‐post immunization (wpi). Immunized and non‐immunized fish died within 2 weeks post‐challenge. Our analyses showed that immunization with A. salmonicida J223 bacterins and antigen preparations did not increase IgM titres. In addition, adaptive immunity biomarker genes (e.g., igm, mhc‐ii and cd4) were down‐regulated. These findings suggest that A. salmonicida J223 antigen preparations hinder lumpfish immunity. Notably, many fish vaccines are bacterin‐based, often lacking efficacy evaluation. This study offers crucial insights for finfish vaccine approval and regulations.