Skin transcriptome of lenok trout (Brachymystax lenok) provides new insight on lectin genes and immune response mechanisms to Aeromonas salmonicida infection.

Brachymystax lenok is an economically valuable cold-water fish species that has shown lower morbidity during pathogen outbreaks compared to other cold-water species. To elucidate the innate immune mechanisms in B. lenok in response to Aeromonas salmonicida infection, the transcriptome sequencing of the skin was performed. A total of 297,142 unigenes were generated, with 64.21 % (190,809) successfully annotated. Differential expression analysis identified 9238 differentially expressed genes (DEGs), with significant enrichment in immune-related pathways, including NOD-like receptor, C-type lectin receptor, and Toll-like receptor signalling pathways. These pathways may play crucial role in pathogen recognition, immune activation, inflammation, and the induction of adaptive immune responses in B. lenok. Further analysis revealed significant upregulation of pro-inflammatory cytokines, complement system components, and antimicrobial peptides such as hepcidin and cathelicidin, highlighting their pivotal roles in B. lenok's immune defense. Moreover, a notable finding was the dynamic expression of various lectin families, including C-type lectins, plectins, galectin-3, and β-galactoside-binding lectins, which are involved in pathogen recognition, immune modulation, and cell signalling. Lectins may also contribute to resistance mechanisms by affecting bacterial membrane permeability, disrupting vital metabolic processes, and enhancing synergy with antimicrobial peptides. In the pathological experiments, histological examination correlated the upregulation of inflammatory mediators and complement components with tissue damage, immune cell infiltration, and lesion development, further supporting the involvement of these genes in the immune response. These results will enrich the information in understanding the immune response in B. lenok, and provide basic data for the following proteomics and functional assays that can verify the protein-level activity of these immune-related genes and clarify their specific roles in host defense and resistance mechanisms. This comprehensive transcriptome analysis provides insights into the immune response mechanisms of B. lenok, with particular emphasis on the role of lectins in pathogen recognition and resistance. These findings offer a foundation for further research on immune mechanisms in fish and the development of therapeutic strategies to mitigate infections in aquaculture.