Enhancement of microbicidal activity in the tiger shrimp Penaeus monodon via immunostimulation

We studied the clearance ability of hemolymph drawn from the tiger shrimp Penaeus monodon immersed in a viable cell suspension of Vibrio vulnificus. Results show that Vibrio cells were largely eliminated from shrimp hemolymph within 12 h following invasion and completely undetectable at 24 h. We also examined the anti-E coli activity of plasma, phenoloxidase (PO) activity, as well as the production of superoxide anion (O-2(-)) by shrimp hemocytes following treatment with each of these 3 immunostimulants. Resultant survival indexes show that some plasma, but not all, exhibits anti-E. coli activity. However, such an activity in all plasma tested could be enhanced by beta-glucan or zymosan up to 24 h following treatment, and slightly enhanced at 6 h following treatment with a Vibrio antigen. PO activity and O-2(-) generation were stimulated by all 3 immunostimulants. Enhanced PO activities were observed from 5 min to 24 h following treatment, with the highest activity occurring at 3 h; the activity recovered to normal on day 3. Increased O-2(-) production was observed from 3-12 h in both glucan- and zymosan-treated shrimp, and at 6 h in shrimp treated with Vibrio antigen. These results show that: (1) some microbicidal reactions may be involved in the clearance of invasive V. vulnificus from shrimp hemolymph; (2) the 3 immunostimulants have the ability to enter shrimp via immersion treatment, thus leading to activation of both the plasma-related factors and hemocytes and the strengthening of PO activity and O-2(-) production; and (3) these enhanced microbicidal reactions exhibit a rapid response that is short in duration.