Abstract:In this study, the effect of beta-glucan on survival rates and the mRNA expression of Lectin and TLR2 in both uninfected and infected Manila clams Ruditapes philippinarum were studied. The results showed that beta-glucan could effectively improve the survival rate of Manila clams infected by Vibrio parahaemolyticus. The survival rate was highest at a beta-glucan concentration of 1000 mg/L. In the gill tissues of the uninfected group (A1 and A2), the TLR2 peaked at 6 h, which was significantly higher than that of other times (P<0.05). In the infected group, TLR2 increased to a peak at 1.5 h and then decreased. Lectin expression in both the infected and the uninfected group increased first and then decreased. The relative expression of Lectin in the A1 group was significantly higher than that of the B1 group at 3 h (P<0.05). In the mantle, the expression of TLR2 in both infected and uninfected groups decreased gradually between 3~12 h. At 24 h, the expression of group A2 was highest. However, in the infected group, the expression of Lectin in 1000 mg/L beta-glucan was higher than at 100 mg/L in the mantle, but there was only a significant difference at 0 h and 24 h (P<0.05). The expression patterns of Lectin in the gill and in the mantle were different, but the feeding of beta-glucan promoted the expression of Lectin during the early stages of infection. From these results, beta-glucan soaking can increase the relative expression of the two genes, and TLR2 and Lectin are expressed more quickly after infection by V. parahaemolyticus when soaked with beta-glucan. The aim of this study is to understand the dose dependent effect conferred by beta-glucan on the immune system and the survival rate of Manila clams, which might provide some theoretical basis for the stock culture, seed breeding and disease control in pond culture of Manila clams.
