Immunomodulatory And Mortality Control Via Β--glucans
For a long time, the most common method for dealing with bacterial infections in aquaculture is the use of antibiotics. However, aquaculture faces serious problems due to various adverse effects of these drugs such as accumulation in the tissue and environmental microbial flora.
The use of antibiotics or vaccines for fish is expensive and many farms cannot use them. Therefore, using substances or additives added to the feed to increase the survival rate of fish and shrimp, disease resistance and growth have been used more frequently and more successfully.
Innate reactions in fish
Similar to mammals, fish have an innate immune system and an adaptive immune system. They are innately responsible for primary reactions. They respond quickly and are not specific. They have no memory for repeated contamination. Adaptability is the responsibility of specific reactions. In other words ,the specific antibody strongly responds for each pathogen.
The most widely known innate immune system cells are macrophages, neutrophils, dendritic cells and natural killer cells. Toll-like receptors located on the surface of immune cells recognize the microbiological pattern and induce an immediate innate immune response. Following this activation and phagocytosis, phagocytic cells present processed fragments of the pathogen to the adaptive immune system and stimulate anti-pathogen responses. Therefore, phagocytic cells are called antigen-presenting cells. Recognition of pathogens by the innate immune system triggers immediate innate defense and activation of adaptive immune responses.
β-glucans: immune system modulator
The ImmunoWall of ICC Brazil is a product composed of the cell wall of Saccharomyces cerevisiae yeast, which is derived from the sugarcane fermentation process for ethanol production. The product contains about 35% of β-glucans and 20% of mannooligosaccharides (MOS). β-glucans are called immune system modulators or stimulants because when they come in contact with phagocytic cells that recognize β-1, 3 and 1, 6, they are stimulated and will produce some cytokines, which will initiate Chains cause immunomodulatory responses and improve the responsiveness of the innate immune system. (figure 1).
This response is particularly important in animals that are initially growing, reproductive stage, stress stage, and environmental challenge; acting as prophylactics and increasing animal resistance, minimizing further damage (eg, decreased performance or high mortality rates). Intensive animal production is a very challenging environment. Therefore, strengthening the immune system may be one of the keys to improving productivity.
MOS is known for its ability to agglutinate pathogens (mostly those with type 1 pili), as well as different gram-negative strains. MOS provides a binding site for pathogens that prevents the colonization of intestinal epithelial cells and these agglutinating bacteria will be excreted with the indigestible part of the fiber (Figure 2).
Performance test of fish
In a recent study conducted by Abu-Elala et al. at the Faculty of Veterinary Medicine at Cairo University in Egypt, Nile tilapia (Oreochromis niloticus, 50.7 ± 0.8g BW) was divided into three experimental groups: control, 0.1% and 0.2% ImmunoWall; 90 fish per treatment (3 replicates/can). Fish performance was measured every 2 weeks during 2 months, and at the end of the experiment, 5 fish/replicates were euthanized to assess clinical pathology, oxidative and antioxidant parameters, relative quantitative PCR of immune gene expression, phagocytosis Activity (%) and index, lysozyme activity (μg/mL). Two months later, the Gram-positive bacteria Lactococcus gravaeie and Gram-negative Aeromonas hydrophila were challenged and the mortality was observed within 1 week.
There was no significant difference in the performance results between the treatments (P> 0.05), however, a numerical increase was observed. The product improved the clinicopathological results of IL1-β and phagocyte and lysozyme activity (WBCs, GPT, GOT, TP and globulin) and relative quantitative PCR expression (P < 0.05). A decrease in g-reductase enzyme activity was observed, and 0.2% product supplementation increased catalase. After two bacterial attacks, mortality rates in both groups decreased (p> 0.05), and both groups were supplemented with immune respiration (Table 1).
Table 1 - Performance, clinicopathological results, oxidative stress,expression of immune-related genes, innate immunity and mortalityparameters of O. niloticus.abMeans with different letters in the same row differ significantly by Tukey test (P<0.05).WBCs: white blood cells. GPT: glutamate pyruvate transaminase. GOT: Glutamate oxalacetatetransaminase. TP: Total protein.
Improve innate immunity
In conclusion, 0.1 and 0.2% of yeast product inclusions can improve the clinical pathological response and innate immunity. ImmunoWall supplements reduced oxidase activity and mortality when challenged with Lacococcus gravaeie and Aeromonas hydrophila compared to the control group. The reduction in mortality after the challenge is consistent, and the survival rate is increased by at least 50% in the case of 100% death due to pathogen contamination.
Other studies have published on the benefits of yeast cell wall supplementation in aquaculture. Ebrahimi et al. (2011) studied the Cyprinus species (Cyprinus carpio) infected with Aeromonas hydrophila and found that the leukocyte survival rate was significantly increased. The increase in feed conversion rate resulted in the increase in the amount of feed in the feed group containing ImmunoWall from 1% to 2.5%. Ebrahimi (2010) reported a decrease in the total number of bacteria in the intestine, and the survival and feed conversion rates of the juvenile Rutilus frisii Kutum fed to ImmunoWall increased by 0.5-2.5%. Karimzadeh et al. (2013) found that Rutilus kutum larvae improved survival, final body weight, and feed conversion rates, and that the total number of bacteria in the 0.5% of intestines supplemented with ImmunoWall was reduced.
Innate immune system regulation
Enhancing and regulating the innate immune system may be one of the strategies to prevent pollution,reduce mortality and increase productivity. If the yeast cell walls in the diet are provided to the animal in advance, the immune system will be regulated and will be alert to many infections or contamination. The action of β-glucan occurs in the innate immune system. In other words, an immune response to pathogen contamination occurs first, avoids more energy consumption during prolonged inflammation, and mobilizes the adaptive immune system faster. Avoid production and high mortality.