Functional role of TrIL-1β in Takifugu rubripes defense against Cryptocaryon irritans infection

The Japanese puffer, Takifugu rubripes , is a commercially important fish species in China that is under serious threat from white spot disease (cyptocaryoniasis), which leads to heavy economic losses. We previously found that interleukin-1 beta (IL-1 beta), an important cytokine with a potential role in resistance against pathogens, was one of the most significantly differentially up -regulated proteins in the gills and spleen of T. rubripes infected by the protozoan parasite Cryptocaryon irritans . In this study, we assessed the potential function of T. rubripes IL-1 beta (TrIL-1 beta) in fish infected with C. irritans . Phylogenetic analysis indicated that the TrIL-1 beta protein sequence was most closely related to that of Atlantic salmon ( Salmo salar ) (67.2 %). The incubation experiments revealed that TrIL-1 beta may reduce trophont activity by destroying membranes. Immunofluorescence experiments showed that recombinant TrIL-1 beta promoted the expression of endogenous IL-1 beta, which penetrated and disrupted the cell membranes of trophonts. Transmission electron microscopy showed that the IL-1 beta group had less tissue damage compared with control groups of fish. IL-1 beta-small interfering RNA and IL-1 beta overexpression experiments were performed in head kidney primary cells, and challenge experiments were performed in vitro. Quantitative RTPCR results showed that TrIL-1 beta regulated and activated MyD88/NF- kappa B and MyD88/MAPK/p38 signaling pathways during C. irritans infection. TrIL-1 beta also promoted the differential expression of IgM , showing that it was involved in humoral immunity of T. rubripes . The cumulative mortality experiment show that TrIL-1 beta could protect fish against C. irritans infection. These results enrich current knowledge about the molecular structure of TrIL-1 beta. They also suggested that recombinant TrIL-1 beta could be used as an adjuvant in a subunit vaccine against C. irritans infection, which is of profound importance for the prevention and control of parasitic diseases in T. rubripes .