Identification and expression of immune genes in the flat oyster Ostrea edulis in response to bonamiosis

Abstract

The European flat Ostrea edulis is highly susceptible to infection by the protozoan Bonamia ostreae and Bonamia exitiosa, intracellular parasites able to survive and proliferate within the oyster haemocytes. The parasite, once phagocytosed by the haemocyte, the main cellular effector of the immune system, appears to have some counter mechanism that turns off the haemocyte's metabolic destructive capacity, so that the parasite survives within the cell. To further understand the molecular basis of the immune response of the flat oyster against the bonamiosis, suppression subtractive hybridization and Q-PCR approaches were combined to identify genes involved in the development of the infection both in early and advanced phases. Four subtractive cDNA libraries were constructed and sequenced, obtaining a high number of ESTs that were seen to be up or down-regulated in the infection. A group of ESTs that play a role in the immune response, such as cytokines, stress proteins, eicosanoids, proteins implicated in phagocytosis and cell junction as well as in transcription signalling were identified and their expression was analysed at different infection levels by Q-PCR. The results here reported can help to enrich our understanding about the immune response of O. edulis against bonamiosis and improve our knowledge of the immune mechanisms of oysters.