LAUSR

Abstract The immune function operation of fish immune organs depends tightly on the immune organs' structural integrity which is mainly regulated by various biological respects such as oxidative status, apoptosis and tight junctions. Previous explorations have documented that dietary (2-carboxyethyl) dimethylsulfonium Bromide (Br-DMPT) intervention boosted fish growth in association with the strengthened immune function of the head kidney, spleen and skin. Here, further exploration was performed to better decipher the primary action mechanisms by which Br-DMPT maintains the immune organs' integrity of fish. In this research, grass carp (Ctenopharyngodon idella) (216.49 ± 0.29 g) as a model were fed five graded levels of Br-DMPT diets (0-520.0 mg/kg) in triplicate for 60 days, followed by a challenge with Aeromonas hydrophila for 2 weeks. Subsequently, immune organ samples were selectively collected to investigate oxidative status, apoptosis and tight junctions associated parameters. Our data from above three immune organs manifested that compared to the control group, 260.0 mg/kg Br-DMPT diet group: (1) markedly decreased oxidative damage degree as evidenced by the obtained lowest value in all oxidative damage indicators and exhibited the highest significant value in almost all antioxidant enzymes activities and corresponding gene expressions, where this action may be in part correlated with the modulation of Nrf2 signalling (P 0.05). Overall, for the first time, our present results confirm that the enhanced structural integrity of immune organs in Br-DMPT- supplemented fish appears to partly be associated with the increased antioxidant status and the inhibited cell apoptosis, as well as the elevated tight junctions, which provides groundbreaking insight into the undiscovered role of Br-DMPT in accelerating fish growth and increases Br-DMPT more potential to be popularly applied in future fishery production.