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Intraperitoneal immunopathological reactions following vaccination of farmed fish. studies of basic immune mechanisms

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Immune reactions to vaccination in farmed fish

Atlantic salmon, rainbow trout and sea bass are three of the species forming part of Europe's farm fishing industry. Their vaccination against certain bacterial diseases is followed by series of immune side effects, with potentially serious consequences for the economy of the industry.

Health

Oil-adjuvant-based vaccines administered to fish populations from all three species have been implicated in the incidence of intraperitoneal immune granulomas. The EGC-VAC project aimed to examine the immunopathological mechanisms involved in granuloma formation in an effort to develop safer vaccines for these species. A number of cell types are involved in the systemic reaction within the peritoneal cavity post-vaccination. Studies showed that in the salmon the interleukin 8 (IL8) and interleukin 1b (IL1b) signal-molecules are produced as an immediate response to vaccination. These molecules in turn attract different cell types, including neutrophils and macrophages to the peritoneal area. In fact, researchers demonstrated that their action is dual. Both types of signal molecules not only attract but also activate the appropriate cell types. The project also showed that one of the cell types taking part in the early responses to vaccination are the eosinophilic granular cells (EGCs). Furthermore, it was established that certain vaccine components cause EGC upregulation. Overall, vaccine formulation, including extracellular products, antigen content and stability, has an effect on the extent of the immune reactions that follow vaccination. Not all three species react to vaccination in the same way, however. In spite of general immunopathological similarities, researchers have established that there are differences in the dynamics of cellular responses among species. In the Atlantic salmon, immune reactions tend to increase for a period of up to 4-6 months, whereas in the rainbow trout responses have subsided after 4 months altogether. On the other hand, in sea bass immune reactions appear milder in severity and with a decreased level of immunological involvement. The study outcomes and observations made throughout the EGC-VAC project have increased our insight into the causes and types of immune reactions in the three fish species following vaccination. This newly established knowledge base is expected to aid safer vaccine development.

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