Comparación de parámetros inmunológicos entre poblaciones de Ostrea edulis con diferente supceptibilidad a la bonamiosis y la especie resistente crassostrea gigas

Resumo

The flat oyster, Ostrea edulis, farming in Europe is suffering a serious setback due to an infectious disease caused by the protozoa Bonamia ostreae. The introduction of the resistant species Crassostrea gigas has been a breathtaking for the farmers whereas the selection of an O. edulis strain tolerant to bonamiosis is reduced to isolated efforts in an Irish farm and in research laboratories in France and Galicia (Spain). Galician populations of O. edulis are living with bonamiosis since the beginning of the outbreak in Europe. In Ireland, still some flat oysters populations are naïve for B. ostreae, whereas others have been selectively breeding after years of coexistence with the infection, showing less susceptibility to bonamiosis in terms of mortality, prevalence and intensity. However, the cellular or molecular bases of this differential susceptibility remain unknown. Looking for a molecular explanation of the differences in intra or interspecific oyster susceptibility to bonamiosis a comparison of some immune parameters in O. edulis and C. gigas was accomplished. In the winter of 2003-04, naïve and tolerant flat oyster groups from Ireland and Galicia and a group of resistant C. gigas were hung up in a Galician area affected by bonamiosis. Haemolymph samples were taken in February and May 2004 and April 2005. In November 2004, new sets of Irish flat oysters and C. gigas were deployed in Ireland and a third haemolymph sampling was performed in June 2005. Several immune parameters were measured: total and diferential haemocyte count (THC and DHC), phagocytic activity, respiratory burst (superoxide anion [O2-], hydrogen peroxide [H2O2] and nitric oxide [NO] productions), several protease (papain- /thermolysin- /trypsin- /quimotrypsin-) inhibitory activity (PIA), bactericidal activity against Vibrio splendidus and Micrococcus spp.(ABA), phenoloxidase (POA), acid phosphatase (APA) and N-ß-acetyl-glucosaminidase (NAGA) activities and heat shock proteins (HSP70) in serum and /or haemocyte lysate supernatant (HLS). The comparison of the parameters was carried out at 3 levels: (1) among O. edulis groups with different susceptibility to bonamiosis, (2) between O. edulis and C. gigas and (3) between Bonamia-infected (BI) and Bonamia non-detected (ND) subgroups of the O. edulis groups. Additionally, in 2006 we focused on interspecific differences in the defence parameters during in vitro interactions of the parasite with haemocyte of both species, with several contact experiments between Bonamia cells and haemocytes of O. edulis or C. gigas, measuring the respiratory burst and the non specific esterase activity (NSE) by flow cytometry. A steadier THC and a bigger proportion of basophilic granulocytes were observed in C. gigas in comparison with O. edulis groups. Similar O2- productions were found between species and lower in the BI subgroups. The H2O2 production was variable among the O. edulis groups and was inhibited in the stimulated C. gigas haemocytes. Generally, C. gigas showed lower PIA, POA, and NAGA than the O. edulis groups. Similar values of phagocytic activity, NO and ABA were found in all the oysters groups. Only APA was higher in C. gigas than in O. edulis groups. All the BI subgroups of O. edulis showed fewer activities than the corresponding ND subgroups except for NAGA. The HSP70 expression was higher in C. gigas, which might be very useful to overcome parasitic infections. The in vitro contact experiments between haemocytes and the parasite showed an inhibition of the respiratory burst and NSE activity in O. edulis haemocytes, whereas these parameters remained unchangeable in the case of C. gigas haemocytes. Some of the analysed parameters may explain, at least in part, the differences in susceptibility to bonamiosis between C. gigas and O. edulis whereas none of them would explain the differences in susceptibility to bonamiosis among O. edulis groups. Overall, the results showed that a higher tolerance to B. ostreae in O. edulis implied a selection restricted to this specific pathogen rather than a more powerful general defence system.