SHK-1

SHK-1 is a spontaneously immortalized cell line derived from primary adherent cell cultures of Atlantic salmon (Salmo salar) head kidney, established by Birgit Helene Dannevig and colleagues at the National Veterinary Institute in Oslo. The head kidney is a hematopoietic organ containing a macrophage-enriched cell population, and SHK-1 proliferating cells appeared after several weeks in culture. Morphologically, SHK-1 cells exhibit a fibroblast-like, flattened and elongated shape, with a near-euploid karyotype, and have been successfully passaged more than 60 times.

The defining advantage of SHK-1 lies in its macrophage‑like phenotype and functional relevance for fish immunology and virology research. The cells express vimentin, react with monoclonal antibodies specific for Atlantic salmon peripheral blood leukocytes, and exhibit strong reactivity for acid phosphatase, non‑specific esterase, Mg²⁺‑dependent adenosine triphosphatase and 5' nucleotidase, while lacking alkaline phosphatase activity - an enzymatic profile characteristic of macrophages. SHK-1 cells also demonstrate limited phagocytic activity against the fish pathogen Aeromonas salmonicida, although no bactericidal activity was observed over a 72‑hour period. Furthermore, SHK-1 expresses major histocompatibility complex (MHC) class I and class II mRNA, the expression of which can be modulated by bacterial components, infectious viruses, and hormonal stimulation, indicating conserved regulatory pathways.

SHK-1 is highly susceptible to infectious salmon anaemia virus (ISAV), making it an indispensable tool for ISA virus propagation, detection, and pathogenesis studies. The cell line has been widely applied to determine the effects of nucleotide concentrations on cell viability, to study the impact of silymarin in aquaculture, and as a model system for investigating innate immunity, antiviral responses and comparative transcriptomics in salmonids. Collectively, SHK-1 represents a robust, renewable resource for fish immunology and virology research, circumventing the ethical and technical limitations of primary leukocyte culture.