The regulatory roles of choline in the immune response induced by LPS and transplantation in pearl oysters Pinctada fucata martensii

Choline (Cho) plays a pivotal role in cellular and organismal homeostasis. In this study, transcriptome and serum immune indicator analysis were used to focus on the immune regulatory roles of Cho in the LPS and transplantation induced immune responses in pearl oysters Pinctada fucata martensii. The oysters (1.5 years old) were divided into four groups: ChoL and ConL (with or without choline pre-treatment prior to LPS), ChoT and ConT (with or without choline pre-treatment prior to transplantation). The results showed that the pearl oysters in the ChoL group have decreased serum levels of TNF-α and IL-17 (P < 0.05), increasing activity of superoxide dismutase (SOD) and catalase (CAT) (P < 0.05), and suppressing NOD-like receptor (NLR) and FoxO signal pathways, compared with the pearl oysters from the ConL group. In the pearl oysters from the ChoT group, the TNF and NF-kappa B signaling pathways, Calmodulin (CaM) genes and serum TNF-α and IL-17 levels (P < 0.05) were suppressed, and SOD and CAT activity were increased (P < 0.05), compared with ConT. In vitro incubation of hemocytes with Cho after 12 and 24 h, the intracellular Ca²⁺ levels were significantly decreased (P < 0.05). Moreover, Cho treatment before transplantation increased the nucleus retention rate of the transplanted pearl oysters. These findings indicate that Cho suppresses immune responses via decreasing pro-inflammatory cytokines (TNF-α and IL-17), enhancing antioxidant enzyme activities, suppressing NLR and other signaling pathways, and modulating calcium homeostasis, ultimately leading to an improved nucleus retention rate, suggesting potential targets for modulating immune responses during pearl production.