Immune gene expression in salmon keratocytes upon bacterial exposure

Pathogens pose a significant threat to farmed salmon, adversely affecting their health and welfare, which results in substantial economic losses. The outermost skin epithelial cells, including skin keratocytes, serve as a critical defense barrier against environmental stressors, such as bacterial infections. Understanding the features and properties of these cells, particularly skin keratocytes, is essential as they play a crucial role in wound healing and tissue regeneration. Additionally, we were curious whether corneal epithelial cells (corneal keratocytes), which protect the fish eye, exhibit similar features and immune functions. To investigate the properties of skin keratocytes, we utilized flow cytometry to analyze scale-derived cells. The analysis revealed that more than 85% of the cells were skin keratocytes, although the remaining cells could not be characterized using this method. Microscopic analysis confirmed that the majority of these cells exhibited the typical morphology of keratocytes and were positive for a pan-keratin antibody. To assess the immune function of skin keratocytes, we exposed scale-derived keratocytes to various fish pathogenic bacteria and evaluated their ability to ingest bacteria and examined the regulation of innate immune genes. Additionally, we analyzed the expression of immune-related markers, including mhcii, in both skin and corneal cells. Our findings demonstrated that scale-derived skin keratocytes internalized bacteria within 3–6 hours of exposure. This bacterial interaction led to the significant upregulation of several key immune-related genes. Interestingly, both skin and corneal cells expressed mhcii, suggesting a potential role in adaptive immunity in addition to their participation in innate immune responses. These results highlight the vital role of skin and corneal cells in the innate immune response against bacterial infections and their possible contribution to adaptive immunity.