beta-1,3-glucans, natural polysaccharide groups, exert immunomodulatory effects to improve the innate response and disease resistance in aquatic species and mammals. However, this beta-glucan stimulant is yet to be assayed in swimming crab (Portunus trituberculatus) hemocytes. In this study, we explored the immunomodulatory effect of beta-1,3-glucans (derived from Euglena gracilis) via in vitro 24 h stimulation assays in swimming crab hemocytes. We found that this algal beta-1,3-glucans in crab hemocytes significantly elevated cellular enzymes related parameters, including phenoloxidase (PO), lysozyme, acid phosphatase (ACP) activities, and superoxide anion generation (O-2(-)) rate both at intracellular (P < 0.05) and extracellular (P < 0.05) levels. Besides, alkaline phosphatase (AKP) in hemocytes exhibited no significant differences across the groups (P > 0.05). beta-glucan significantly influenced (P < 0.05) the activities of the antioxidant enzyme, superoxide dismutase (SOD) in hemocytes. Moreover, the relative mRNA expression of numerous immune-related genes, including proPO, TLR2, Alf-1, NOX, Lysozyme, Crustin-1, and Cuznsod, was significantly higher stimulated hemocytes than in control (P < 0.05). We also reported the dose-dependent antiparasitic activity against Mesanophyrs sp., in stimulated hemocytes than in the control (P < 0.05). The present study collectively demonstrated that beta-glucan potentially stimulates innate immunity by elevating cellular enzyme responses and up-regulating the mRNA expression of genes associated with crab innate immunity. Thus, beta-glucan is a promising immunostimulant for swimming crab farming in crustaceans aquaculture.
