The Comparative Immunological Study On Two Scallops Chlamys Farreri And Argopecten Irradians

Scallop aquaculture is a big industry and contributes enormously to the economic development of coastal provinces in China. Since the summer of 1997, large-scale mortality of cultured scallop has caused catastrophic losses to scallop aquaculture, which resulted in the production decreasing drastically. There are a range of factors causing the mortality, which could be divided into three subgroups as pathogens, breed degeneration and deteriorative environment. Intensive investigation on scallop immune defense mechanism, looking for ways to enhance resistance to diseases and improving breed quality would be the final solution to the problems of scallop aquaculture and would be of great importance to sustainable development of aquaculture in China.In this paper, comparative study on immune parameters of Zhikong scallop and bay scallop was executed under both stress and stressless condition. The comparison of HSP70 and HSP90 gene expression between the two scallops under heavy metal stress was made. This will help to better understanding the internal defense mechanisms of scallop immunity, to select disease-resistant strains, and provide basic data for diseases prevention in shellfish aquaculture.Flow-cytometric method was adopted to determine hemocyte mortality, phagocytosis capacity and the respiratory burst of Zhikong scallop and bay scallop. There were slightly differences in hemocyte mortality and respiratory burst between the two scallops. But the phagocytosis rate in bay scallop was significantly higher than that of Zhikong scallp. In haemolymph and hepatopancreas, bay scallop had a significantly higher SOD and ACP activities than Zhikong scallop. MDA content in bay scallop was also higher, but there was no significant difference between the two scallops. In the Vibrio anguilarum infection experiment, Zhikong scallop displayed a higher accumulated mortality rate. It indicated that bay scallop was more capable of destroying invading pathogens and protect organism from oxidative damage than Zhikong scallop.Under the stress of different Pb2+ stress, the haemocyte mortality rate was lower in bay scallop than that of Zhikong scallop. Bay scallop also had a higher phagocytosis rate and respiratory burst. Measurement of humoral immunity parameter showed that SOD, ACP activities and MDA content was higher in bay scallop than in Zhikong scallop. These parameters demonstrated both scallops encountered oxidative stress exposed to Pb2+ but the immunity of bay scallop was less affected.The full length cDNA of bay scallop Argopecten irradians HSP90 (designated AiHSP90) was cloned by the techniques of homology cloning and rapid amplification of cDNA ends (RACE). It was of 2669 bp, including a 5'-terminal untranslated region (UTR) of 90 bp, a 3'-terminal UTR of 404 bp with a canonical polyadenylation signal sequence AATAAA, a poly (A) tail, and an open reading frame (ORF) of 2175 bp encoding a polypeptide of 724 amino acids, with a predicted molecular weight of 83.08 kDa and theoretical isoelectric point of 4.81.Fluorescent real-time quantitative RT-PCR was used to examine the expression pattern of AiHSP90 mRNA in haemocytes of scallops challenged by Gram-negative bacteria Vibrio anguillarum and Gram-positive bacteria Micrococcus luteus. In both bacterial challenged groups, AiHSP90 mRNA level increased and reached maximal level at 9h after injection and then dropped progressively. The increase of AiHSP90 transcript was higher in V. anguillarum challenged groups than that in M. luteus challenged groups, which suggested that V. anguillarum was a stronger inducer of AiHSP90. This is the first time such a response of HSP90 has been observed in a molluscan species, which indicated that AiHSP90 was involved in scallop's response to bacteria infection. Such data could help to understand the significance of HSP expression to scallop immune defence.Fluorescent real-time quantitative RT-PCR was used to examine the mRNA expression pattern of HSP70 and HSP90 from Zhikong scallop (designated CfHSP70 and CfHSP90, respectively) and bay scallop (designated AiHSP70 and AiHSP90, respectively) in haemocytes of scallops under the stress of different concentrations of Cd2+, Pb2+ and Cu2+. CfHSP70 mRNA expression was at high level after 10 days of Cd2+ or Pb2+ exposure. After 20 days of exposure, CfHSP70 in Cd2+ group recovered to nearly the same level of control group and in Pb2+ group CfHSP70 also displayed a trend to decline. On the contrary, AiHSP70 mRNA expression reached high level only after 20 days of Cd2+ or Pb2+ exposure. Cu2+ treatment showed similar effects on both HSP70s of the two scallops. But a higher induction of HSP70 was observed in bay scallop. For the same heavy metal, different concentrations led to different induction of HSP70. For HSP90, AiHSP90 showed a higher expression than CfHSP90 in all the three heavy metal treated groups and a longer exposure induced higher expression of AiHSP90. For the same heavy metal, different concentrations led to different induction of HSP90. The results indicated that gene expression manner of HSP70 and HSP90 was different under heavy metal stress. Considering bay scallop living better under stress, which was demonstrated in the former experiments, the comparison of HSPs gene expression between the two scallops under heavy metal stress indicated that higher expression of Zhikong scallop HSP70 implied weaker resistance to stress while higher expression of bay scallop HSP90 implied stronger resistance to stress. Further investigations on more stress experiments such as heat, pathogen challenges shoud be carried out to testify the deduction.