Study on immune regulation in Hyriopsis cumingii Lea: Effect of pearl-nucleus insertion in the visceral mass on immune factors present in the hemolymph

This study was aimed at elucidating the mechanism of immune responses in fresh water mussels during pearl culture. Alpha-2 macroglobulin gene (α2M) expression, acid phosphatase (ACP) and superoxide dismutase (SOD) activities, and hemocyte counts were evaluated after inserting a pearl nucleus into the visceral mass of Hyriopsis cumingii Lea (H. Lea). We selected 60 H. Leas and randomly assigned them to 2 groups (each group contained 3 replicates of 10 individuals), and individuals among one group were treated by inserting pearl nucleus into the visceral mass. Real-time quantitative polymerase chain reaction (Q-PCR) was used to evaluate α2M gene expression, and the activities of ACP and SOD in hemocytes and serum were determined after 1, 2, 3, 5, and 10 days after nucleus insertion. Hemocyte morphologies and numbers on the 5th day after insertion were studied using phase-contrast microscope (PCM), optical microscope and flow cytometry (FCM). All observations suggested that the insertion of the pearl nucleus in the visceral mass had a significant effect on α2M gene expression, ACP and SOD activities, and hemocyte characteristics. The α2M gene expression was sharply up-regulated on the 3rd day after nucleus insertion, and it was significantly higher in the test groups on the 3rd, 5th, and 10th days than those in the control groups (P < 0.05). On the 1st to 3rd after treatment, ACP activity in the test group was higher than that in the control group (P < 0.05). SOD activity in the serum was remarkably higher in the test groups than in the control group, and exhibited significant differences on the 3rd, 5th, and 10th days (P < 0.05). However, the SOD activity in hemocytes was lower in the test group than in the control group, and it exhibited significant differences on all days, except on the 3rd day (P < 0.05). The hemocytes were divisible into 2 types: granulocytes (GR) and hyalinocytes (HY). The hemocyte morphology, protuberances, vesicle-like bodies, and density increased significantly (P < 0.05), and the number of GR increased, while that of HY decreased after nucleus insertion. These results indicated that the insertion of pearl nucleus enhanced the immune response in H. Lea.