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C-type lectin is a type of calcium-dependent sugar recognition protein, which plays an important role in recognizing invading microorganisms as non-self and assists in the clearance of pathogenic microorganisms. In this study, a C-type lectin homolog was identified from Penaeus vannamei (PvCTL2) using RACE-PCR method and functionally characterized in detail. The open reading frame (ORF) of PvCTL2 was 1143 bp, encoding 380 amino acids, which contained a conservative carbohydrate recognition domain (CRD) and a low-density lipoprotein receptor (LDLR) domain A. The predicted molecular weight was 41.79 kDa and the theoretical isoelectric point was 6.27. PvCTL2 was relatively high expressed in muscle, intestine, heart, nerve, and hepatopancreas, and Vibrio parahaemolyticus challenge could significantly upregulate the expression level of PvCTL2 in muscle. Agglutination test of recombinant protein of PvCTL2 in vitro showed that rPvCTL2 was a Ca2+-dependent C-type lectin, which could agglutinate five types of bacteria, including Gram-negative bacteria and fungi, as well as bind different concentrations of monosaccharides. RNAi-based silencing of PvCTL2 gene resulted in significantly higher mortality rate when shrimp was challenged with Vibrio parahaemolyticus, and the median lethal time was significantly shorter than the control. These results suggested that PvCTL2 could be involved in the immune response against bacterial challenge and contributed to non-self recognition as a pattern recognition receptor in the innate immune system of shrimp P. vannamei. [ABSTRACT FROM AUTHOR]

Twenty-three species of dry Traditional Chinese herbs (TCHs) were examined for the experiment. Bacteriostasis experiments in vitro were carried out for screening 23 TCHs on inhibiting Vibrio harveyi and four screened species (Galla chinensis, Terminalia chebula, Scutellaria baicalensis, Rheum officinale) which have antibacterial activity were decoct, concentrated, and mixed with diets at 2%, respectively. After feeding for 28 days, shrimps were challenged by V. harveyi, and then mortality was recorded. With regard to hemocyte phagocytic activity, activities of lysozyme (LZM) were measured on day 0, 7, 14, 21, and 28. Relative percentage survival (RPS) was also investigated in each TCH group. Phagocytic activity (PA) phagocytic index (PI), LZM, and RPS (with the exception of T. chebula and R. officinale) of Pacific white shrimp can be significantly increased when fed 2% TCH extracts. RPS of S. baicalensis was the highest, reaching 51.86% on day 28, then the G. chinensis group, whereas R. officinale group was the lowest, when the Pacific white shrimp challenged with V. harveyi. It can be concluded that S. baicalensis and G. chinensis could be used to enhance shrimp's immunity and disease resistance in cultured Pacific white shrimp. [ABSTRACT FROM AUTHOR]