Stress-associated β-glucan administration stimulates the TLR-MYD88-NFKB1 signaling pathway in Nile tilapia (Oreochromis niloticus)

There is evidence that the administration of beta-glucan can effectively activate several defense mechanisms, such as the Tlr-Myd88-Nfkb1 pathway that induces the expression of immune cytokines. Thus, the objective of this work was to evaluate whether beta-glucan acts on the mechanisms of gene transcription via the Tlr-Myd88-Nfkb1 pathway in Nile tilapia under stress after challenge with Streptococcus agalactiae. Therefore, we evaluated the expression of immune system genes such as toll-like receptors 1 (tlr1), toll-like receptors 2 (tlr2), primary myeloid differentiation response gene (myd88) and nuclear factor kappa B1 (nfkb1). A total of 408 fish were distributed in 24 polyethylene boxes and randomly divided into eight groups with 3 replications each: C15: Tilapias received a control diet (free of beta-glucan) for 15 days and were sampled after the 15th day of the experiment; C15D: Tilapias received a control diet (free of beta-glucan) for 15 days, were challenged on the 14th day and were sampled at the 15th day of the experiment; beta 15: Tilapias received experimental diet (1g kg  1 of beta-glucan) for 15 days and were sampled after 15 days; beta 15D: Tilapias received an experimental diet (1g kg  1 of beta-glucan) for 15 days, were challenged on the 14th day and were sampled at the 15th day of the experiment; C30: Tilapias received a control diet (free of beta-glucan) for 30 days and were sampled on the 30th day of the experiment; C30D: Tilapias received a control diet (free of beta-glucan) for 30 days, were challenged on the 29th day and were sampled at the 30th day of the experiment; beta 30: Tilapias received experimental diet (1g kg-1 of beta-glucan) for 30 days and were sampled after 30 days and beta 30D: Tilapias received experimental diet (1g kg  1 of beta-glucan) for 30 days, were challenged on the 29th day and were sampled at 30 of the experiment. In the fish sampled at 15 and 30 days of the experiment, after being anesthetized and killed by brain section, cranial kidney and spleen were collected for gene expression analysis. The analyzes showed that the association of beta-glucan and stressful management modulated the immune system, using the Tlr-Myd88-Nfkb1 signaling pathway, indicating that this compound can be used to promote early defense and protect fish against diseases.