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Monogeneans of the genus Gyrodactylus are well-known pathogens causing huge mortalities in wild and cultured fish. Cytokine expression is one of most important host defense mechanisms against parasite infections. In this study, the expression pattern of the key pro-inflammatory (IL-1β, IL-8, IFN-γ, TNF-α, IL-12 and iNOS) and anti-inflammatory cytokine genes (IL-10, TGFβ and IL-4) of Gyrodactylus kobayashii infected goldfish (Carassius auratus) were determined by real-time quantitative PCR analysis. Our results showed that G. kobayashii infection caused increased expression of the pro-inflammatory cytokines including IFN-γ, TNF-α and iNOS in all detected tissues throughout the infection period. Among these genes, iNOS has the highest transcript level accompanied with increased nitric oxide (NO) concentration in the serum of all infected goldfish. The mRNA level of IL-1β in the liver, spleen and head kidney was significantly up-regulated during the early stage of infection (days 2-8). While high expression level of IL-8 and IL-12 was observed during the elimination phase of infection (days 10-14). As for anti-inflammatory cytokines, the expression profiles of IL-10 were distinct from those of TGF-β and IL-4. Specifically, the mRNA level of IL-10 did not increase in the spleen and head kidney during the early stage of infection, while increased expression of TGF-β and IL-4 were likewise seen. Besides, all infected fish had significantly higher complement C3 but lower IgM levels than the non-infected fish. The results provide insights into the interaction between gyrodactylids and the fish host, and indicate that systemic cytokine responses are critical for controlling parasite infection in fish., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Modulation of innate immune activity and oxidative stress response of Pangasianodon hypophthalmus through experimental infection with (Thaparocleidus sp.) dactylogyrid monogenean was studied. A standard cohabitation method was used to infect healthy experimental fish. After 14 days, dactylogyrid (gill monogenean) infested fish were sampled and categorised into three different infected groups namely (T1) low (<10 mean dactylogyrid per gill arch per fish), (T2) moderate (10-49 mean dactylogyrid per gill arch per fish) and (T3) high (>50 mean dactylogyrid per gill arch per fish) along with a control group T0 (un-infested fish). Serum and tissues (gills and liver) were collected from experimental fish and analyzed for markers of innate immune and oxidative stress, respectively. The results showed that respiratory burst activity, myeloperoxidase level, serum lysozyme, α-2 macroglobulin and total serum immunoglobulin level were significantly (p < 0.05) elevated in fish with different degrees of parasite infestation compared to the control (un-infested group). Similarly, cellular oxidative biomarkers superoxide dismutase, catalase, glutathione-S-transferase and Na + -K + -ATPase activities of gills and liver were significantly (p < 0.05) elevated in dactylogyrid infested fish in comparison to the control. However, significantly decreased level of albumin, albumin to globulin ratio, total serum antiprotease and ceruloplasmin were observed in fish infested with low degree of dactylogyrids, while no significant differences in these parameters were observed between moderately infested and the control groups. The results suggested that varying degree of gill monogenean dactylogyrid infestation not only modulated the innate immune response of P. hypophthalmus by lowering albumin, total serum antiprotease and ceruloplasmin and inducing respiratory burst activity, phagocytic activity, myeloperoxidase, lysozyme, α-2 macroglobulin and total immunoglobulins, but also the oxidative stress biomarkers. The baseline data obtained in the present study will be valuable in understanding the host-parasite relationship and the dynamics of innate, oxidative stress responses and susceptibility of P. hypophthalmus to different degrees of parasitosis., (Copyright © 2017 Elsevier Ltd. All rights reserved.)