Immunological Responses to Bacterial Pathogens in Eel Species

Eel species such as Anguilla anguilla and Anguilla japonica possess a multifaceted immune system that integrates innate barriers, cellular defences and adaptive mechanisms to contend with bacterial pathogens. The primary sites of immune activity include the skin and gill mucosa, where antimicrobial peptides, lectins and lysozyme constitute the first line of defence. Beneath this, phagocytic cells in the head kidney and spleen patrol for invading bacteria, initiating inflammatory cascades via pattern‐recognition receptors such as toll‐like receptors. Subsequent activation of complement pathways, pro‐inflammatory cytokine release and antigen presentation coordinate the recruitment and maturation of B and T lymphocytes. B cells secrete specific immunoglobulins in serum and mucus, while cytotoxic T cells eliminate infected cells. Recent advances in transcriptomics and proteomics have revealed the dynamic regulation of immune‐related genes, cytokines and antimicrobial effectors during infection with Vibrio anguillarum, Edwardsiella tarda and Aeromonas hydrophila. Understanding these responses is critical for the development of targeted vaccines and immunostimulants, with the dual aim of improving eel health in aquaculture and mitigating economic losses associated with bacterial disease outbreaks.

Research from Nature Portfolio

Recent studies have employed high‐throughput transcriptome sequencing to characterise gene expression in European eel immune organs following Vibrio anguillarum challenge. These analyses revealed upregulation of genes encoding pro‐inflammatory cytokines (such as interleukin‐1β and tumour necrosis factor‐α), complement factors and antimicrobial peptides, signalling a robust innate response. Complementary proteomic profiling of skin mucus in Japanese eel infected with Edwardsiella tarda identified an expanded repertoire of lectins and lysozyme isoforms that collectively enhance mucosal barrier integrity. Furthermore, functional genomics approaches utilising CRISPR interference have demonstrated that disruption of toll‐like receptor 5 impairs flagellin recognition and diminishes recruitment of macrophages and neutrophils to the site of infection. Together, these studies elucidate the coordinated interplay between mucosal and systemic defences and underscore key molecular targets for vaccine design.

Immunological Responses to Bacterial Pathogens in Eel Species publication trend

The graph below shows the total number of articles in immunological responses to bacterial pathogens in eel species across all publications each year (not limited to Nature Index journals).

Technical terms

Toll‐like receptor (TLR): A class of pattern‐recognition receptors that detect conserved bacterial molecules (for example lipopolysaccharide or flagellin) and initiate innate immune signalling.

Antimicrobial peptide (AMP): Small, cationic peptides produced by epithelial and immune cells that disrupt bacterial membranes and modulate immune responses.

Lysozyme: An enzyme present in mucus and serum that hydrolyses bacterial cell‐wall peptidoglycan, contributing to direct bacterial killing.

Complement system: A cascade of plasma proteins that opsonise pathogens, recruit immune cells and form membrane‐attack complexes.

Head kidney: A primary haematopoietic and immune organ in teleost fish, analogous to mammalian bone marrow and lymphoid tissues.

References

1. Immunogenicity of a bivalent protein as a vaccine against Edwardsiella anguillarum and Vibrio vulnificus in Japanese eel (Anguilla japonica). MicrobiologyOpen (2018).