Functional Characterization of Hexacorallia Phagocytic Cells

Area of Science:

• Marine biology
• Immunology
• Cell biology

Background:

• Phagocytosis is a vital cellular defense mechanism in innate immunity, crucial for eliminating pathogens and cellular debris.
• In hexacorallians (corals and sea anemones), the mechanisms of phagocytosis and the identity of phagocytic cells remain poorly understood.
• Previous histological studies suggested the presence of phagocytic cells, termed amoebocytes, in anthozoans.

Purpose of the Study:

• To identify and characterize phagocytic cells in the coral *Pocillopora damicornis* and the sea anemone *Nematostella vectensis*.
• To elucidate the functional capabilities of these phagocytes, including their targets and intracellular processes.
• To establish a foundational understanding of hexacorallian immune cell biology.

Main Methods:

• Utilized fluorescence-activated cell sorting and microscopy to isolate and analyze distinct cell populations.
• Employed various antigens (bacteria, fungal antigens, beads) to assess phagocytic uptake.
• Investigated intracellular processes by examining phagolysosome formation, pH, and the role of actin filaments and reactive oxygen species (ROS).

Main Results:

• Identified distinct populations of phagocytic cells capable of engulfing bacteria, fungal antigens, and synthetic beads.
• Demonstrated that these phagocytes also engulf self, damaged cells, indicating a role beyond pathogen clearance.
• Confirmed that engulfed antigens localize to low pH phagolysosomes where degradation occurs, and that actin rearrangement is essential for efficient phagocytosis.
• Correlated cellular markers for lysolysosomal vesicles and reactive oxygen species (ROS) with identified hexacorallian phagocytes.

Conclusions:

• Established the presence and function of phagocytic cells in *Pocillopora damicornis* and *Nematostella vectensis*.
• Provided evidence that hexacorallian phagocytes handle both foreign and self-derived antigens, similar to other invertebrates.
• Highlighted the importance of phagolysosome formation, low pH, and actin dynamics in hexacorallian phagocytosis.
• Laid the groundwork for future research into the complexities of innate immunity in corals and sea anemones.