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Abstract

In this review paper, we summarize the immune system of penaeid shrimp. This review includes the clotting system comprising clot protein and clotting enzyme (transglutaminase II), as well as the prophenoloxidase (proPO) activation system including proPO-activating enzyme (PPAE), proPO and clip domain serine protease homolog (c-SPH). In addition, several shrimp cytokines or cytokine-like molecules found in tiger shrimp Penaeus monodon participating in the defense responses are also discussed. C-SPH could enhance hemocyte adhesion. Shrimp astakine promoted hemocyte proliferation in the hematopoietic tissues and could be down-regulated at the post-transcriptional level by the binding of intracellular molecules such as transglutaminase I and crustin Pm4 to its 3’-untranslatd region. Penaeidin is found to be a dual function molecule as an antimicrobial peptide and an autocrine-acting cytokine. Yet, other antimicrobial substances such as quinone and melanine which are generated during the proPO activation pathway and the reactive oxygen and nitrogen intermediates (ROI and RNI) which are generated during the phagocytic process can also kill and clear the invading microorganisms directly. In addition, Dscam (Down syndrome cell adhesion molecule), a member of the immunoglobulin superfamily (IgSF) which plays an essential role in the alternative adaptive immune system of invertebrates, has also been characterized in shrimp. Penaeid shrimp is one of the most important commercially available aquaculture resources. Although, the culture techniques and field management skills have significantly improved in the recent years, infectious diseases are still a threat to the industry. The study of shrimp immune system could be important in designing the strategies against pathogen infection. For shrimp, the innate immune responses play a major role in combatting invading pathogens and prevent them against diseases. The immune responses involve different factors such as physical barrier, bacteria clearance, encapsulation, clotting reactions, prophenoloxidase system, reactive oxygen intermediates, and antimicrobial activity. The innate immune system uses a variety of pattern recognition receptors (PRR) on the hemocyte membrane to detect the pathogenassociated molecule pattern (PAMP) and transduce signals during pathogen invasion. Hemocytes are then activated and the defense molecules are degranulated against the pathogens.

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