Modulation of selected inflammatory responses and non-specific defenses in Atlantic salmon induced by beta-1,3/1,6-glucans (Macrogard®)

The anadromous nature and long production cycle of Atlantic salmon (Salmo salar L) demands for vaccination regimes to maintain long-term protective immunity in vaccinated fish. While prime vaccination is largely based on injectable vaccines, that in order to produce sufficient protection need to be formulated with potent adjuvants, these vaccines also produce undesirable side-effects in the form of inflammatory processes at the site of injection. In many species, immune responses can be modulated by beta-glucans, and this practice have gained prominence also because these subtances prove to be potential adjuvants for oral vaccines. In scientific reports from mammalian studies, beta-glucans have also been reported to modulate inflammatory processes. Hence, the main objective of the this study was to investigate the ability of (1,3)(1,6)- beta-D-glucans (BDG) to enhance non-specific immune mechanisms, and to modulate inflammatory reactions to vaccination in Atlantic salmon (Salmo salar L). Data generated in this study shows that mucus and serum from vaccinated fish fed with beta-glucan diet had antibacterial properties over serum from control fed fish, based on the ability to inhibit the propagation Micrococcus luteus, Citrobacter freundii and Yersinia ruckeri at different temperature in vitro. As for bacteria neutralization assays, serum lysozyme showed significant inhibition of M. luteus during the early post vaccination period that gradually declined to the same level as the control group as the post vaccination period increased further. On the contrary, mucus ldid not inhibit M. luteus growth. The kinetic of immune and inflammatory gene expression showed an inverse relationshion between the beta-glucan fed fish and control group in that there was a significant upregulation of genes such as TNFa-3, IL-6 and IFNγ in the early timepoints soon after vaccination in the beta-glucan fed group unlike the control group that had insignificant expression of these genes. Overall, this study shows that the β-1,3/1,6 glucan administered in the current study (Macrogard®) is a potent immunostimulant able to enhance the innate immune responses in vaccinated fish. As for modulatory effects on inflammation, the observed differenes yielded promising observations, suggesting that further in vivo studies should be carried out. Future studies should seek to determine the optimal dose and duration of exposure able to produce highest protection in vaccinated fish leaving both animal welfare and economical benefits to the Norwegian aquaculture sector.Aquamedic.ASsubmittedVersionM-A