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Published on: August 11, 2014
Francisella noatunensis subsp. noatunensis invades, survives and replicates in Atlantic cod cells
Kathrine R Bakkemo1, Helene Mikkelsen, Audny Johansen
1PHARMAQ AS, 0213 Oslo, Norway.
Abstract:
Systemic infection caused by the facultative intracellular bacterium Francisella noatunensis subsp. noatunensis remains a disease threat to Atlantic cod Gadus morhua L. Future prophylactics could benefit from better knowledge on how the bacterium invades, survives and establishes infection in its host cells. Here, facilitated by the use of a gentamicin protection assay, this was studied in primary monocyte/macrophage cultures and an epithelial-like cell line derived from Atlantic cod larvae (ACL cells). The results showed that F. noatunensis subsp. noatunensis is able to invade primary monocyte/macrophages, and that the actin-polymerisation inhibitor cytochalasin D blocked internalisation, demonstrating that the invasion is mediated through phagocytosis. Interferon gamma (IFNγ) treatment of cod macrophages prior to infection enhanced bacterial invasion, potentially by stimulating macrophage activation in an early step in host defence against F. noatunensis subsp. noatunensis infections. We measured a rapid drop of the initial high levels of internalised bacteria in macrophages, indicating the presence and action of a cellular immune defence mechanism before intracellular bacterial replication took place. Low levels of bacterial internalisation and replication were detected in the epithelial-like ACL cells. The capacity of F. noatunensis subsp. noatunensis to enter, survive and even replicate within an epithelial cell line may play an important role in its ability to infect live fish and transverse epithelial barriers to reach the bacterium's main target cells-the macrophage.
Insights
Francisella noatunensis subsp. noatunensis invades Atlantic cod macrophages via phagocytosis, with interferon gamma enhancing entry. The bacterium
Area of Science:
- Fish immunology
- Bacterial pathogenesis
- Cellular microbiology
Background:
- Francisella noatunensis subsp. noatunensis poses a significant disease risk to Atlantic cod (Gadus morhua L.).
- Understanding host-pathogen interactions is crucial for developing effective prophylactics against this bacterial infection.
Purpose of the Study:
- To investigate the invasion mechanisms of Francisella noatunensis subsp. noatunensis in Atlantic cod host cells.
- To elucidate the role of macrophages and epithelial cells in the early stages of infection.
Main Methods:
- Utilized a gentamicin protection assay to quantify intracellular bacterial survival.
- Employed primary monocyte/macrophage cultures and an Atlantic cod larval epithelial cell line (ACL cells).
- Investigated the effect of cytochalasin D and interferon gamma (IFNγ) on bacterial invasion.
Main Results:
- Francisella noatunensis subsp. noatunensis invasion into macrophages is mediated by phagocytosis, inhibited by cytochalasin D.
- Interferon gamma (IFNγ) treatment enhanced bacterial uptake by cod macrophages, suggesting a role in immune activation.
- Macrophages exhibited a rapid reduction in intracellular bacteria, indicating an early immune response, while epithelial cells showed lower invasion and replication.
Conclusions:
- Francisella noatunensis subsp. noatunensis utilizes phagocytosis to invade Atlantic cod macrophages.
- Epithelial cells may facilitate bacterial dissemination and access to target macrophages, contributing to systemic infection.
- Early immune responses in macrophages limit bacterial proliferation, but epithelial cell interaction is key for infection establishment.
