Spirulina elicits the activation of innate immunity and increases resistance against Vibrio alginolyticus in shrimp.

The effect of Spirulina dried powder (SDP) on the immune response of white shrimp Litopenaeus vannamei was studied in vitro and in vivo. Incubating shrimp haemocytes in 0.5 mg ml(-1) SDP caused the degranulation of haemocytes and a reduction in the percentage of large cells within 30 min. Shrimp haemocytes incubated in 1 mg ml(-1) SDP significantly increased their phenoloxidase (PO) activity, serine proteinase activity, and respiratory burst activity (RB, release of superoxide anion). A recombinant protein of lipopolysaccharide and ß-1,3-glucan binding protein (LGBP) of the white shrimp was produced, named rLvLGBP, and examined for its binding with SDP. An ELISA binding assay showed that rLvLGBP binds to SDP with a dissociation constant of 0.0507 µM. In another experiment, shrimp fed diets containing SDP at 0 (control), 30, and 60 g kg(-1) after four weeks were examined for LGBP transcript level and lysozyme activity, as well as phagocytic activity, clearance efficiency, and resistance to Vibrio alginolyticus. These parameters were significantly higher in shrimp receiving diets containing SDP at 60 g kg(-1) or 30 g kg(-1) than in controls. In conclusion, shrimp haemocytes receiving SDP provoked the activation of innate immunity as evidenced by the recognition and binding of LGBP, degranulation of haemocytes, reduction in the percentage of large cells, increases in PO activity, serine proteinase activity, superoxide anion levels, and up-regulated LGBP transcript levels. Shrimp receiving diets containing SDP had increased lysozyme activity and resistance against V. alginolyticus infection. This study showed the mechanism underlying the immunostimulatory action of Spirulina and its immune response in shrimp.

White shrimp Litopenaeus vannamei that had received the hot-water extract of Spirulina platensis showed earlier recovery in immunity and up-regulation of gene expressions after pH stress.

White shrimp Litopenaeus vannamei which had been immersed in seawater (35‰, pH 8.2) containing the hot-water extract of Spirulina platensis at 0 (control), 200, 400, and 600 mg L(-1) for 3 h, were transferred to seawater at pH 6.8, and the immune parameters and transcripts of the lipopolysaccharide- and ß-glucan-binding protein (LGBP), peroxinectin (PX), and integrin ß (IB) were examined 6-96 h post-transfer. Shrimp with no exposure to the hot-water extract and no pH change served as the background control. Results indicated that the hyaline cells, granular cells (including semi-granular cells), total haemocyte count, phenoloxidase activity, respiratory burst, superoxide dismutase activity, glutathione peroxidase activity, and lysozyme activity of shrimp transferred to seawater at pH 6.8 significantly decreased to the lowest at 6 h post-transfer. These immune parameters of shrimp immersed in 600 mg L(-1) of the extract were significantly higher than those of control shrimp at 24-96 h post-transfer, and had returned to the background values earlier at 48-72 h post-transfer with significant transcripts of LGBP, PX, and IB at 24, 6, and 24 h, respectively, whereas these parameters of control shrimp returned to the original values at ≥96 h post-transfer.

Administration of the hot-water extract of Spirulina platensis enhanced the immune response of white shrimp Litopenaeus vannamei and its resistance against Vibrio alginolyticus.

White shrimp Litopenaeus vannamei which had been injected with the hot-water extract of Spirulina platensis at 6, 10, and 20 microg g(-1), or immersed in aerated seawater containing extract at 200, 400, and 600 mg L(-1) were challenged with Vibrio alginolyticus at 1.5 x 10(6) or 1.4 x 10(6) colony-forming units (cfu) shrimp(-1), and then placed in seawater. Survival rates of shrimp that received the extract of S. platensis at 6-20 microg g(-1), and those of shrimp immersed in seawater containing the extract at 400 and 600 mg L(-1) were significantly higher than those of control shrimp after 24-96 and 48-96 h, respectively. In a separate experiment, the hyaline cell (HC) count, granular cell (GC, including semi-granular cell) count, total haemocyte count (THC), phenoloxidase (PO) activity, respiratory burst (RB), superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, and lysozyme activity were measured when shrimp were injected with the extract at 6, 10, and 20 microg g(-1), and immersed in seawater containing the extract at 200, 400, and 600 mg L(-1). These parameters directly increased with the concentration, and significantly increased when shrimp were immersed in the seawater containing the extract at 0.5-4 h. L. vannamei that received all doses of the extract via injection or via immersion all had increased phagocytic activity and clearance efficiency to V. alginolyticus at 12-72 h and 3-4 h, respectively. It was concluded that L. vannamei that received the hot-water extract of S. platensis had enhanced innate immunity and increased resistance against V. alginolyticus infection.