Earlier Activation of Interferon and Pro-Inflammatory Response Is Beneficial to Largemouth Bass (Micropterus salmoides) against Rhabdovirus Infection

In order to understand the immune response of largemouth bass against Micropterus salmoides Rhabdovirus (MSRV), assisting disease resistance breeding, three largemouth bass breeding varieties Micropterus salmoides "Youlu No 3" (U3), "Youlu No 1" (U1) and "Zhelu No 1" (P1) were challenged intraperitoneally with MSRV. Serum and tissues were sampled to study the changes in non-specific immune parameters, viral loads, and transcript levels of immune-related genes, and the cumulative mortality rate was recorded daily for 14 days. The results showed that the cumulative mortality rates in the U1, P1, and U3 groups were 6.66% +/- 2.89%, 3.33% +/- 2.89%, and 0, respectively. The higher mortality may attribute to the increased viral loads after infection in the liver (2.79 x 10(5) and 2.38 x 10(5) vs. 1.3 x 10(4) copies/mg), spleen (2.14 x 10(5) and 9.40 x 10(4) vs. 4.21 x 10(3) copies/mg), and kidney (3.59 x 10(4) and 8.40 x 10(3) vs. 2.42 x 10(3) copies/mg) in the U1 and P1 groups compared to the U3 group. The serum non-specific immune parameters (lysozyme, catalase, and acid phosphatase) were found to be increased significantly in the U3 group. In addition, the transcripts of interferon-related genes (IFN-gamma, IRF3, and IRF7) and pro-inflammatory-related genes (TNF-alpha and IL-1 beta) exhibited up-regulation and peaked at 6 h post infection in the U3 group, which also exhibited up-regulation but peaked at 12-24 h post infection in the U1 and P1 groups. In conclusion, these findings indicate that earlier activation of interferon and pro-inflammatory response is beneficial to largemouth bass against MSRV infection. This experiment may provide an insight into understanding the immune mechanism of largemouth bass against MSRV infection and contributes to molecular-assisted selection.