Differential time-series expression of immune-related genes of Pacific white shrimp Litopenaeus vannamei in response to dietary inclusion of β-1,3-glucan

Time-series changes in transcript abundance of nine genes encoding important immune proteins in haemocytes or hepatopancreas of Pacific white shrimp Litopenaeus vannamei fed daily in a 1-week feeding trial diets containing three levels (0%, 0.2% or 1%) of β-1,3-glucan from Schizophyllum commune were quantified by real-time PCR. As a whole, the immune modulation elicited by β-glucan is bimodal, one swift reaction of up- or down-regulation occurred within 24 h and a delayed regulation was commenced as late as 3–7 days. Haemocyanin, crustin, prophenoloxidase (proPO) and transglutaminase (TGase) did not respond to the glucan treatment. While penaeidin 3 (Litvan PEN3) was swiftly down-regulated (0–24 h), lysozyme and cytosolic manganese superoxide dismutase (cMnSOD) were swiftly up-regulated (0–24 h). In contrast, the two pattern recognition proteins (PRPs), β-glucan binding protein–high density lipoprotein (BGBP-HDL) and lipopolysaccharide/β-glucan binding protein (LGBP), showed a delayed up-regulation. Their expressions were not maximized until as late as 72 h or 7 days, respectively, which coincide with the initiation of reported immune enhancement (6–24 days) of PO and SOD activity, phagocytosis and superoxide anion production in penaeid shrimp receiving glucan-containing diet. These immune responses could be the downstream effects of the two PRP gene up-regulation that predispose the shrimp to a state of high immune responsiveness. Increased dosage of β-glucan from 2 to 10 g kg−1 diet did not affect the expressions of the genes, indicating the sufficiency of β-glucan supplementation at 2 g kg−1 diet.