Time-course analysis of peroxinectin mRNA in the shrimp Litopenaeus vannamei after challenge with Vibrio campbellii

Peroxinectin (Pox), which promotes cell adhesion and encapsulation of bacteria in crustaceans, is synthesized in granular and semigranular hemocytes. In this study, real-time PCR was used to quantify Pox transcripts in individual tissues of the Pacific white shrimp, Litopenaeus vannamei, over 48 h following injection of a sublethal dose of the shrimp pathogen Vibrio campbellii. The resulting data were used to infer the movements of hemocytes among the tissues in response to bacterial challenge. Over all times and treatments, Pox transcripts (ng total RNA)(-1) varied by orders of magnitude among individual tissues, such that circulating hemocytes >> gills >> heart lymphoid organ hepatopancreas approximately muscle. Relatively low constitutive expression of Pox in the lymphoid organ compared to circulating hemocytes, gills, and heart supports a primary role for this organ in bacteriostasis and degradation, rather than encapsulation of invasive bacteria. Numbers of Pox transcripts increased significantly at the injection site within 4 h and remained significantly elevated for 48 h, consistent with a rapid and sustained recruitment of hemocytes to the site of injection. Transcripts increased significantly in the gill but not in other tissues over the time-course of this experiment. These expression data reinforce the role of the gill in trapping and encapsulating invasive bacteria as a primary strategic focus during the early phase of the crustacean immune response and, by comparison with earlier studies of lysozyme expression in the same tissues, suggest differential roles for various tissues in a successful immune response.