Corals and sea anemones have at least two populations of immune cells and that these specialized cells make up about 3% of the total cell population, according to new research.
Snyder et al. show that distinct populations of phagocytic cells in cauliflower corals (Pocillopora damicornis) and starlet sea anemones (Nematostella vectensis) engulf bacteria, fungal antigens, and beads. The image shows a cauliflower coral cell challenged with Staphylococcus aureus. Yellow arrow shows an internalized, pH-activated Staphylococcus aureus particle that fluoresces bright green at a low pH. White arrows indicate the cocci bacterial particles. Staphylococcus aureus particles are fluorescent after the fusion of the bacteria with the lysolitic vesicle, which leads to lowered pH. Scale bar – 10 μm. Image credit: Snyder et al., doi: 10.3389/fimmu.2021.662803.
“Phagocytosis is the cellular defense mechanism used to eliminate antigens derived from dysregulated or damaged cells, and microbial pathogens,” said Dr. Nikki Traylor-Knowles, a researcher in the Rosenstiel School of Marine and Atmospheric Science at the University of Miami, and her colleagues.
“Phagocytosis is therefore a pillar of innate immunity, whereby foreign particles are engulfed and degraded in vesicles.”
“In corals and sea anemones, phagocytic mechanisms are poorly understood.”
In their new study, the researchers exposed foreign particles such as bacteria, fungal antigens, and beads into the cauliflower coral (Pocillopora damicornis) and the starlet sea anemone (Nematostella vectensis).
They then isolated different cell populations using fluorescence-activated cell sorting and microscopy.
They found that specialized cells called phagocytes engulfed the foreign particles, while small, fluid-filled structures inside the cells, called phagosomes, worked to destroy the invaders as well as their own damaged cells.
“Our findings are important because they show that corals have the cellular capabilities to fight infection and that they have unique cell types that were previously not known,” Dr. Traylor-Knowles said.
“We need to have a better understanding of how coral cells perform specialized functions such as fight infections as the climate change crisis drastically reduces global coral reef biomass and diversity worldwide.”
“Our findings can help in the development of diagnostic tools for assessing coral health.”
The study was published in the journal Frontiers of Immunology.
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Grace A. Snyder et al. Functional Characterization of Hexacorallia Phagocytic Cells. Front. Immunol, published online July 26, 2021; doi: 10.3389/fimmu.2021.662803
