White shrimp Litopenaeus vannamei hemocytes receiving fucoidan release endogenous molecules that activate and synergize innate immunity in the presence of fucoidan

Fucoidan is widely acknowledged as an immunostimulant and used to increase immune parameters of shrimp and resistance against pathogen in aquaculture. The present study evaluated the effect of shrimp hemocytes receiving fucoidan. White shrimp Litopenaeus vannamei hemocytes receiving fucoidan at 1 mg ml(-1) exhibited a reduction in the percentage of viable hemocytes, caused cell necrosis in hemocytes, and released endogenous molecules, namely EM-F with three major bands at 71, 72, and 73 kDa in Coomassie blue stain, and six bands at 23, 47, 62, 72, 73, and 180 kDa in silver stain. An analysis of LC-MS/MS identified that EM-F contained HMGBb, HSP90, H2A, H2B, H4 and other immune-related molecules like tubulin, organellar Rab, SOD, crustin I, KPI, sarcoplasmic calcium-binding protein, GTP-binding nuclear protein, and single VMC domain. Shrimp hemocytes receiving fucoidan, EM-F, and the mixture of fucoidan plus EM-F (fucoidan + EM-F) increased their phenoloxidase (PO) activity and respiratory burst (RB). PO activity and RB in shrimp hemocytes receiving the mixture of fucoidan + EM-F were significantly higher than in shrimp hemocytes receiving fucoidan alone and EM-F alone. In conclusion, shrimp hemocytes receiving the non-self-molecule fucoidan undergo a necrosis of hemocytes and dying cells that release the endogenous molecules, EM-F that leads to the downstream activation and synergization of innate immunity in the presence of fucoidan.