Biorigin, 18680-900, Lençóis Paulista, São Paulo, Brazil.
Department of Ocean Sciences, Memorial University, St. John's, NL, A1C5S7, Canada.
Fish Shellfish Immunol. 2021 May;112:56-63. doi: 10.1016/j.fsi.2021.02.014. Epub 2021 Feb 25.
The effects of dietary β-glucan on innate immune responses have been shown in a number of different vertebrate species. However, there is conflicting information about the period of administration (shorter vs. longer), and it is also unclear to what extent β-glucan's effects can be observed post-treatment in fish. Thus, we fed Nile tilapia for 0 (control group; 45 days of control diet), 15 (30 days of control followed by 15 days of β-glucan), 30 (15 days of control followed by 30 days of β-glucan) or 45 days with a diet containing 0.1% of β-glucan (MacroGard®). We evaluated the growth performance at the end of the β-glucan feeding trial and the innate immune function immediately after the feeding trial and 7 and 14 days post-feeding trial. In addition, at day 10 post-feeding trial, we assessed the tilapia's resistance against a bacterial infection. No significant differences were observed in growth performance between the groups; however, fish fed with β-glucan for 30 and 45 days had higher (approx. 8%) relative weight gain compared to the control. Regardless of the administration period, fish fed with β-glucan had higher innate immune responses immediately after the feeding trial such as lysozyme activity in plasma, liver and intestine and respiratory burst compared to the control, and in general these differences were gradually reduced over the withdrawal period (up to 14 days). No differences were observed in the plasma hemolytic activity of the complement or myeloperoxidase activity in plasma or intestine. Moreover, fish from the control group had early mortalities (2 vs. 4-5 days post-infection, respectively) and a lower survival rate (60 vs. 80%, respectively) compared to fish fed with β-glucan for 15 or 30 days, and, interestingly, fish fed for 45 days with β-glucan had no mortality. This study indicates that regardless of the administration period (i.e., 15 up to 45 days), the β-glucan improved the innate immune responses and the tilapia's resistance to disease, and this protection could be observed up to 10 days post-feeding trial, adding in vivo evidence that β-glucan may contribute to a trained innate immunity. Additionally, we showed that a longer period of administration did not cause immunosuppression as previously hypothesized but promoted further growth and immune performance. These findings are relevant to the aquaculture industry and demonstrate that a longer β-glucan feeding protocol may be considered to achieve better results.
β-葡聚糖对先天免疫反应的影响在许多不同的脊椎动物物种中都有报道。然而，关于给药时间（较短与较长）的信息存在矛盾，而且β-葡聚糖的作用在鱼类中治疗后能持续多久也不清楚。因此，我们用含有 0.1%β-葡聚糖（MacroGard®）的饲料喂养尼罗罗非鱼 0（对照组；45 天对照饮食）、15（30 天对照饮食后 15 天β-葡聚糖）、30（15 天对照饮食后 30 天β-葡聚糖）或 45 天。我们在β-葡聚糖喂养试验结束时评估生长性能，在试验结束后立即以及试验结束后 7 天和 14 天评估先天免疫功能。此外，在喂养试验结束后 10 天，我们评估了罗非鱼对细菌感染的抵抗力。各组之间的生长性能没有显著差异；然而，喂养 30 天和 45 天β-葡聚糖的鱼比对照组的相对增重率更高（约 8%）。无论给药时间如何，喂养β-葡聚糖的鱼在试验结束后立即具有更高的先天免疫反应，如血浆、肝脏和肠道中的溶菌酶活性和呼吸爆发，一般来说，这些差异在停药期（长达 14 天）逐渐减少。在血浆补体溶血活性或血浆或肠道髓过氧化物酶活性方面没有差异。此外，与喂养 15 天或 30 天β-葡聚糖的鱼相比，对照组的鱼更早死亡（分别为感染后 2 天和 4-5 天），存活率更低（分别为 60%和 80%），有趣的是，喂养 45 天β-葡聚糖的鱼没有死亡。本研究表明，无论给药时间（即 15 至 45 天）如何，β-葡聚糖都能提高先天免疫反应和罗非鱼对疾病的抵抗力，这种保护作用可持续至喂养试验结束后 10 天，为β-葡聚糖可能有助于训练有素的先天免疫提供了体内证据。此外，我们还表明，与之前假设的相反，较长时间的给药不会导致免疫抑制，反而会促进进一步的生长和免疫性能。这些发现与水产养殖业有关，表明较长时间的β-葡聚糖喂养方案可能会产生更好的效果。
