Response of lysozyme activity to Vibrio anguillarum infection in different tissues of Scapharca broughtonii

In order to effectively prevent the harm of bacteria and other pathogenic microorganisms to S. broughtonii, we observed the response process of the lysozyme activity in different tissues of S. broughtonii infected by Vibrio anguillarum, and explored the immune function of the lysozyme in the body of S. broughtonii. In this experiment, 20-month-old S. broughtonii individuals were infected by injecting live bacteria, and 16 individuals were randomly selected. And 1 mL (about 1×10⁹ bacteria) V. anguillarum suspension was injected into the axe foot of each individual as the infection group. 16 randomly selected individuals were not injected with V. anguillarum as the control group. The two groups were cultivated in clean seawater for 4, 12, 24 and 48 h. In each group, randomly selected 4 S. broughtonii individuals were dissected for the blood, mantle, gill, axe foot, hepatopancrea and adductor muscle tissues. The concentration of lysozyme was determined by ELISA kit. The results showed that for the invasion of V. anguillarum, the lysozyme content in the blood of S. broughtonii rapidly increased from the normal low value and maintained a high level, indicating that the blood is one of the main immune tissues of S. broughtonii body defending against pathogen. In the case of no infection, S. broughtonii mantle always maintained a high lysozyme concentration to prevent the interference of the external water environment. The concentration of lysozyme in infected gills and axe foot are significantly higher than the normal values after the injection for 24 hours, indicating that the mantle, gills and axe foot were the first barriers for S. broughtonii body to contact with the outside world which can also respond to the invasion of pathogenic bacteria, but the response was delayed compared with the blood. The lysozyme content of hepatopancrea and adductor muscle did not change significantly. And it was speculated that hepatopancrea and adductor muscle were not important immune tissues or organs of S. broughtonii. The results of this study can provide relevant parameters for the study of disease resistance and immune mechanism of S. broughtonii.