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Knowledge on the innate and adaptative immune factors involved in the response of Sparus aurata to enteromyxosis

Innate immune factors.
Cellular response. In head kidney (HK), the percentage of acidophilic granulocytes, and the leucocyte peroxidases content, phagocytosis and respiratory burst activity decreased significantly at different sampling times, whereas the cytotoxic activity was greatly enhanced (up to 2.3 times) in recipient respect to control fish. In donor fish, peroxidase content was higher and respiratory burst was significantly lower in the gut associated lymphoid tissue (GALT) than in the HK leucocytes. Cytotoxic activity was higher in HK than in GALT leucocytes, and also higher in parasitized versus non-parasitized fish.Humoral factors. Alternative complement activity and peroxidase content in serum were lower, higher or similar in recipient fish respect to controls depending on the sampling time. At day 10 p.e., recipient fish showed a higher peroxidase content and a lower complement activity than those of controls. Cytokine expression. A contrary effect of the exposure to the parasite on pro-inflammatory cytokine mRNA expression in HK was demonstrated. Il-1b expression was enhanced and TNFa depleted in recipient fish respect to control fish.

Adaptative immune factors.
Immunoassays were applied to determine the presence of specific anti-E. leei antibodies in the sera of gilthead sea bream exposed to infection. The presence of specific antibodies was finally analysed using immunohistochemistry (IHQ), as the developed ELISA assay lacked specificity. The presence of specific anti-E. leei antibodies was confirmed in the sera of infected fish and those which had overcome infections. In cohabitation experiments, positive fish were observed from 52 days post-exposure and onwards. The percentage of positive fish was slightly higher in exposed levamisole-treated (RT) than in exposed untreated (RC) fish. Specific antibodies were more frequently found in non-parasitized than in parasitized fish.

In conclusion, several immune factors of gilthead sea bream are affected by enteromyxosis, and both innate and adaptative immunity are involved in the response to infection. Leucocyte cytotoxic activity might play an important role, whereas specific antibodies were detected after a minimum of about 50 days post-exposure. The observed immune response in this fish host could contribute to keep the infection controlled.

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Reported by

Universidad de Murcia (UMU)
Universidad de Murcia (UMU),Dept. Biología Celular, Facultad de Biología, Campus de Espinardo
30100 Murcia
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