Antimicrobial activity of a serine proteinase inhibitor SPIPm5 from the black tiger shrimp Penaeus monodon.

A two-domain Kazal-type serine proteinase inhibitor, SPIPm5, from Penaeus monodon was studied. Its transcript was expressed in all tissues tested including the hemocytes, stomach, gill, lymphoid organ, muscle, intestine and heart albeit less in hepatopancreas and eyestalk. The expression of SPIPm5 gene was also up-regulated by heat stress, white spot syndrome virus (WSSV) infection and yellow head virus (YHV) infection. Injection of recombinant rSPIPm5 protein into normal shrimp to mimic heat stress condition did not have or had little stimulating effect on the expression of other immune genes: crustinPm1, penaeidin3, penaeidin5, Hsp70, SPIPm2 and SPIPm5. Like some other proteinase inhibitors, the rSPIPm5 could inhibit the hemolymph proPO activity. In survival experiments, the rSPIPm5 could prolong the life of WSSV-infected shrimp similar to the effect of heat stress. The rSPIPm5 also helped the YHV-, Vibrio harveyi- and V. parahaemolyticus-infected shrimp survive longer. The increased endurance against microbial infection was due to the inhibitory effects presumably activated by rSPIPm5 on viral replication and bacterial growth but not the expression of antimicrobial peptides. Therefore, the SPIPm5 plays an important role in shrimp innate immunity against the viral and bacterial infection.

Characterization of PmSpӓtzle 1 from the black tiger shrimp Peneaus monodon.

Spätzle is a signaling ligand in innate immune response that signals pathogenic infection via Toll receptor and Toll pathway into the cells for the synthesis of antimicrobial proteins. Herein, three PmSpӓtzle isoforms were identified in Penaeus monodon, namely PmSpz1, 2 and 3. The PmSpz1 was chosen for detailed study. The PmSpz1 gene was expressed in all nine tissues tested including the hemocytes, stomach, hepatopancreas, gill, lymphoid tissue, eyestalk, muscle, intestine and heart. Its expression was up-regulated upon white spot syndrome virus (WSSV) infection. Western blot analysis of hemolymph showed that the PmSpz1 mostly existed as a cleaved active form awaiting to activate the Toll pathway. Injection of a recombinant PmSpz1 rendered the shrimp less susceptible to the WSSV infection. Injection of a recombinant active form of PmSpz1 into a normal shrimp activated the synthesis of crustinPm1, crustinPm7, ALFPm3, penaeidin3 but not penaeidin5 indicating that the expression of all antimicrobial proteins but not penaeidin5 was under the regulation of Toll pathway.