Similar to the previous study (70), here the expression of igt was much higher than that of igm in the gut, and in systemic tissues, the expression level of igm was significantly higher than that of igt. Moreover, similar to our study, the expression of igt in the hindgut was significantly stronger than that in the spleen or head kidney after vaccination with an oral vaccine against IHNV (71), virus-specific IgM and IgT were found to be significantly elevated in systemic and mucosal tissues, respectively, in rainbow trout after infection with IHNV (72). Here, CD40LG is linked to infection.