Expression of Mhc class I and II mRNA in a macrophage-like cell line (SHK-1) derived from Atlantic salmon, Salmo salar L., head kidney

A cell-line derived from Atlantic salmon (Salmo salar L.) head kidney (SHK-1) consisting of macrophage-like cells was investigated for major histocompatibility complex (Mhc) class I and class II messenger ribonucleic acid (mRNA) expression following stimulation with lipopolysaccaride (LPS), human recombinant insulin-like growth factor-I (IGF-I), and virus infection. A reverse transcriptase-polymerase chain reaction (RT-PCR) was used to provide a semi-quantitative comparison of specific mRNA levels. Incubation with LPS from Escherichia coli (100 μg ml−1) resulted in a decrease in the expression of Mhc class I heavy chain mRNA after 24 h followed by a weak increase or slightly reduced expression. Incubation with LPS from Aeromonas salmonicida subsp. salmonicida (10 μg ml−1and 100 μg ml−1) induced a more marked reduction in expression after 24 h than LPS from E. coli, and a greater increase in expression after 72 h. Similar observations were also recorded with respect to Mhc class II mRNA expression. Following infection with two different viruses that are pathogenic for Atlantic salmon (infectious salmon anaemia (ISA) virus, and infectious pancreatic necrosis (IPN) virus), the level of expressed mRNA for both Mhc classes increased at 24 h post-infection, whereas the level was markedly reduced or absent 72 h post-infection. IGF-I (10 μg ml−1and 100 μg ml−1) induced either a reduction or absence of Mhc transcripts following 3 h and 48 h incubation. The present study shows that a cell-line consisting of macrophage-like cells expresses Mhc class I and class II, and that the expression can be modified in response to bacterial components, infective viruses, and hormonal stimulation. The study demonstrates a link in expression between the two Mhc classes, indicating common regulatory mechanisms.