Innate and adaptive immune responses of turbot, Scophthalmus maximus (L.), following experimental infection with Enteromyxum scophthalmi (Myxosporea: Myxozoa)

Sharpsnout sea bream (Diplodus puntazzo) humoral immune response against the parasite Enteromyxum leei (Myxozoa)

The humoral innate immune response of sharpsnout seabream Diplodus puntazzo against the myxozoan Enteromyxum leei was studied. Enteromyxosis was transmitted by cohabitation and a group of uninfected fish served as control. At 5, 12, 19, 26, 40 and 55 days post-exposure (p.e.), control and recipient fish were sampled to determine the prevalence of infection and some humoral innate immune parameters (antiprotease, antitumoral and peroxidase activities). Prevalence of infection was high from day 12 p.e. and reached 100% at days 40 and 55, when intensity of infection was medium to severe. The antiprotease activity was significantly increased in E. leei-exposed fish with respect to control fish at days 12 and 19 p.e. The serum antitumoral activity was slightly lower in recipient than in control fish at all sampling times, except at 40 days p.e., though no statistically significant differences were observed. Serum peroxidases were higher in all recipient fish than in control ones, with the highest stimulation index at 40 days p.e. Within recipient fish, no differences were detected between sampling times in any of the measured activities. The possible implication of these immune factors in the high susceptibility of D. puntazzo to this enteromyxosis is discussed.

Cell-mediated cytotoxicity is the main innate immune mechanism involved in the cellular defence of gilthead seabream (Teleostei: Sparidae) against Enteromyxum leei (Myxozoa)

The cellular innate immune response of gilthead seabream (Sparus aurata L.) against the myxozoan Enteromyxum leei was studied. Enteromyxosis was transmitted by maintaining uninfected fish (recipients) together with infected animals. A group of fish not exposed to the infection served as controls. After 10, 22, 38, 52 and 108 days, control and recipient fish were sampled and leucocyte subpopulations and cellular immune responses (leucocyte peroxidases, phagocytosis, respiratory burst and cytotoxicity) of the head-kidney leucocytes were determined. The percentage of acidophilic granulocytes was significantly lower in non-parasitized and parasitized recipient fish than in control fish after 22 days but no significant differences were seen between non-parasitized and parasitized recipient animals. The leucocyte peroxidase content, phagocytosis and respiratory burst activity were seen to have decreased significantly at different sampling times in both non-parasitized and parasitized recipient fish with respect to the controls, whereas cytotoxic activity was up to 2.3 times higher than in control fish. Within the recipient group, little difference was observed in the studied parameters between non-parasitized and parasitized fish. These data demonstrate that cytotoxic activity may have an important role in the defence of gilthead seabream against the myxosporean E. leei. Immunological implications of E. leei infections are discussed.

Response of Ig-positive cells to Enteromyxum scophthalmi (Myxozoa) experimental infection in turbot, Scophthalmus maximus (L.): A histopathological and immunohistochemical study

In recent years, a new parasite that causes severe losses has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis that affected all portions of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was set up to gain insights into the immune response of fish against this parasitic infection. The kinetics of immunoglobulin positive (Ig+) cells in spleen, kidney and intestine from turbot experimentally infected with E. scophthalmi was studied. For evaluating both the progress of infection and the lesions induced by the parasite, we performed histopathological studies and for detecting Ig+ cells in situ we used an indirect immunohistochemical method. In fish exposed to the parasite, the number of Ig+ cells significantly increased in the intestine, the target organ of the parasite, whereas in spleen and kidney, haematopoietic organs where the parasite was not detected, the number of Ig+ cells decreased. Furthermore, the pattern of distribution of Ig+ cells changed in all three organs examined in recipient/infected fish compared with control fish (not exposed to the parasite). The results obtained in this study indicate that the infection by E. scophthalmi in turbot induced an immune response that involved changes in the number and distribution of Ig+ cells.