Cellular and humoral immune response of European sea bass (Dicentrarchus labrax L.) (Teleostei : Serranidae) immunized with Sphaerospora dicentrarchi(Myxosporea : Bivalvulida)

The immune response of European sea bass after intracaelomic immunization w ith Sphaerospora dicentrarchi was studied. Fish were injected with S. dicen trarchi spores (DIC), with spores plus adjuvant (DIC + FCA), with adjuvant alone (FCA) or with PBS. Several parameters of the immune response were mea sured. Serum lysozyme increased significantly in DIC fish 1 week after immu nization (p.i.) and it remained significantly higher in DIC + FCA fish 4 we eks p.i., and in DIC fish 8 weeks p.i. than in PBS-injected fish. The numbe r of nitroblue tetrazolium-positive blood cells was significantly higher in DIC + FCA fish 1, 4 and 8 weeks p.i, but the highest values were detected 1 week p.i. The highest stimulation index was detected in phagocytes from D IC + FCA fish. The number of S. dicentrarchi antibody-secreting cells was s ignificantly higher in DIC + FCA fish than in DIC fish. Serum from DIC and DIC + FCA fish, stained the polar capsules and the valves of S. dicentrarch i spores in immunohistochemistry. Serum antibodies could not be detected us ing immunoblot assay. All these results show that immunization with S. dice ntrarchi resulted in the activation of the non-specific immune response, ma inly 7 days p.i. A specific humoral response against the parasite was also demonstrated but it had a low magnitude.