Phycobiliprotein Extract from Arthrospira platensis Boosts Immune Function in Pacific Oysters (Magallana gigas)

The utilization of functional feeds in oyster hatcheries to reduce disease-related issues and improve health in the prespawning period is expected to become essential in the near future. In the present study, an aqueous extract of phycobiliproteins (CBPs) sourced from the cyanobacterium Arthrospira platensis was tested as an immunomodulatory agent in the Pacific oyster (Magallana gigas). Adult oysters were given three distinct treatments with the aqueous extract of CBPs (2, 20 or 80 μg/mL) for 24-96 h. In vivo analysis demonstrated that the extract of CBPs enhanced phagocytosis, lysosomal content and mitochondrial membrane potential levels, but inhibited the production of reactive oxygen species in hemocytes of oysters. Higher concentrations of the extract (80 μg/mL) had a more rapid effect on phagocytosis, with significant differences found after the first 24 h of the experiment. Lower concentrations of the extract (2 μg/mL) enhanced the phagocytic activity of hemocytes at later stages of its administration. Additionally, the expression profiles of the hsp70 and hsp90 genes were monitored in gills from oysters exposed to the extract at concentrations of 2, 20 and 200 μg/mL for 48 h, considering their roles in regulating the innate immune system in bivalves. The results show that hsp70 expression was down-regulated during the first 24 h of administration, whereas it recovered to control levels after 48 h. In contrast, the expression levels of hsp90 were up-regulated throughout the entire period of extract administration. Combined, the results of the present study show that the aqueous extract of CBPs from A. platensis can rapidly enhance the cellular immune response in Pacific oysters, and could potentially be used as an immunomodulator in bivalve hatcheries.