Infection-induced changes in expression of antibacterial and cytokine genes in the gill epithelial cells of Atlantic cod, Gadus morhua during incubation with bacterial pathogens

The molecular processes of immune responses in mucosal tissues, such as the gills, during infection with bacterial pathogens are poorly understood. In the present study, we analyzed the transcriptional profiles of selected antibacterial genes and cytokines in the gills of a cold-water fish, Atlantic cod, Gadus morhua following in vitro infection with bacterial pathogens, Vibrio anguillarum and atypical Aeromonas salmonicida using semi-quantitative RT-PCR. There was significant upregulation in the transcripts of the antibacterial genes: bactericidal permeability-increasing protein/lipopolysaccharide-binding protein (BPI/LBP), g-type lysozyme, transferrin, metallothionein, galectin and hepcidin at 3 h post-incubation with the two pathogens. The expression of cathelicidin in the gills was significantly enhanced by A. salmonicida, but not by V. anguillarum. At 24 h post-incubation, most of these genes were still significantly upregulated, although some genes returned to their basal expression levels. The transcription levels of cytokines such as interleukin (IL)-1β, IL-8 and interferon (IFN)-γ significantly increased at 3 h post-incubation with the pathogens. IL-22 and CC-chemokine type 1 transcripts were enhanced by A. salmonicida, but not by V. anguillarum. There was down-regulation of expression in CC-chemokine type-2 and -3 by V. anguillarum, while the expression levels of IL-10 remained unchanged upon infection with either of the two bacterial pathogens. The early upregulation of antibacterial genes in the gills could signal the onset of the acute phase response following bacterial infection and the differential modulation of some cytokine genes could be related to host–pathogen interactions that trigger immune response cascades in mucosal tissues of the host.