L-fucoside localization in the gills of the genus Takifugu and its possible implication in the parasitism of Heterobothrium okamotoi (Monogenea: Diclidophoridae)

Background: The monogenean parasite Heterobothrium okamotoi only parasitizes the gills of Takifugu rubripes. In this study, we hypothesized that the carbohydrates contribute to high host specificity of H. okamotoi.Methods: T. rubripes, T. niphobles, T. snyderi, and T. pardalis were used for UEA I staining of the gills and an in vivo challenge test against H. okamotoi. To examine the effect of L-fucose, an in vitro detachment test was conducted using the host's gills. Additionally, fucosylated proteins were isolated from the membrane proteins of T. niphobles gills.Results: The location of L-fucoside and the infection dynamics in four species were correlated to some extent; H. okamotoi detached relatively quickly from T. niphobles possessing L-fucoside both on the surface of the gills and in certain types of cells, including mucus cells, but detached slowly from T. snyderi possessing L-fucoside in only certain types of cells, including mucus cells. Under the conditions examined, H. okamotoi exhibited minimal detachment from T. rubripes and T. pardalis, and L-fucoside was not detected. The significantly higher detachment rate of H. okamotoi from the host's gills incubated in L-fucose-containing medium compared with the controls suggests that L-fucose in the non-host gills induced detachment of H. okamotoi. Four fucosylated proteins, including mucin5AC-like, were identified as potential factors for the detachment of H. okamotoi.Conclusions: Fucosylated proteins covering the surface of non-host gills might contribute to H. okamotoi detachment.General significance: This research shows the possible involvement of oligosaccharides in the host specificity of monogenean parasites.