# Development and Evaluation of Immunoprotective Efficacy of Membrane Protein Vaccine Against Scuticociliatosis

## TL;DR

This study developed a membrane protein vaccine against a parasitic disease in turbot fish, showing strong immune protection and identifying key molecular mechanisms.

## Contribution

The novel membrane protein vaccine for turbot scuticociliatosis demonstrates superior immunoprotective efficacy and provides insights into its molecular mechanisms.

## Key findings

- The membrane protein vaccine significantly increased serum IgM levels and immune enzyme activities in turbot.
- Transcriptomic analysis identified 1063 differentially expressed genes linked to immune response pathways in vaccinated turbot.
- The vaccine reduced parasite presence at wound sites by up to 87.79% after challenge.

## Abstract

Objective: To develop a novel and efficient vaccine for controlling scuticociliatosis in turbot (Scophthalmus maximus), this study targeted the parasitic ciliate Pseudocohnilembus persalinus for membrane protein vaccine preparation. Methods: The immunoprotective efficacy and underlying molecular mechanisms of the vaccine were systematically evaluated through immunization–challenge experiments, immune parameter detection, and transcriptomic analysis. Results: Results showed that the serum IgM level in turbot immunized with the membrane protein vaccine reached its peak one week after the second immunization, which was significantly higher than that in the control group and the whole-cell protein vaccine group (p < 0.05). Additionally, the activities of serum peroxidase (POD), total superoxide dismutase (T-SOD), acetylcholinesterase (ACH), and lysozyme (LZM) were significantly enhanced (p < 0.05). At 24 h and 48 h post-challenge, the relative parasite reduction rates at the wound sites in the membrane protein vaccine group were 87.79% and 74.17%, respectively. Transcriptomic analysis revealed 1063 differentially expressed genes (DEGs) in the spleen tissue of turbot immunized with the membrane protein vaccine, including 734 upregulated and 329 downregulated genes. These DEGs were significantly enriched in pathways such as glycine, serine and threonine metabolism and one carbon pool by folate, which are involved in immune responses by regulating immune cell proliferation, antioxidant defense, and immune substance synthesis. Conclusions: This study successfully developed a P. persalinus membrane protein vaccine with excellent immunoprotective efficacy and elucidated its molecular mechanisms of protection. It provides a novel vaccine candidate for the green control of turbot scuticociliatosis and offers a theoretical basis and technical support for the development of fish parasite subunit vaccines.