A preliminary investigation on the protective effects of β-glucan and mannan induced trained immunity in pufferfish Takifugu obscurus

Immune stimuli are able to trigger long-term protective effects through mechanisms of trained immunity, which has attracted increasing attention. Although the existence of trained immunity has evidenced in teleost fish, while there were no such reports in pufferfish (Takifugu obscurus) so far. Therefore, the present study aimed to evaluate the induction of beta-glucan and mannan on the trained immunity and their protective efficacy against Vibrio harveyi re-stimulation in pufferfish. beta-glucan and mannan induction of trained immunity in head-kidney primary leukocytes is accompanied by a strong increase in immediate ROS burst, cumulative NO production and lactate concentrations after V. harveyi re-stimulation. In addition, beta-glucan and mannan-treated pufferfish exhibited reduced bacterial loads in multiple tissues, a rapid and long-term elevated inflammatory response in head kidney during secondary V. harveyi infection. Notably, immune receptors dectin-1 and dectin-2, and cytokines tnfsf14 and il-1 beta exhibited comparatively upregulation to the beta-glucan training, while NK-lysin and faslg showed stronger response to the mannan training post V. harveyi stimulation, implying the different signaling pathway activated post beta-glucan and mannan training. Subsequent markers for immune training including abundance of genes encoding glycolytic enzymes (hk1, pfkla, and ldha) and transcription factors (mtor and hif1 alpha), as well as increased acetylation levels were elevated in the beta-glucan and mannan trained pufferfish, depicting heightened glycolysis following beta-glucan and mannan training. These results collectively demonstrated that beta-glucan and mannan both induced protective responses against V. harveyi infection probably through mediating distinct signaling pathway in pufferfish, and studies are underway to harness its potential applicability for prime and boost vaccination strategies.