Abstract
Phagocytosis is the cellular defense mechanism used to eliminate antigens derived from dysregulated or damaged cells, and microbial pathogens. Phagocytosis is therefore a pillar of innate immunity, whereby foreign particles are engulfed and degraded in lysolitic vesicles. In hexacorallians, phagocytic mechanisms are poorly understood, though putative anthozoan phagocytic cells (amoebocytes) have been identified histologically. We identify and characterize phagocytes from the coral Pocillopora damicornis and the sea anemone Nematostella vectensis. Using fluorescence-activated cell sorting and microscopy, we show that distinct populations of phagocytic cells engulf bacteria, fungal antigens, and beads. In addition to pathogenic antigens, we show that phagocytic cells engulf self, damaged cells. We show that target antigens localize to low pH phagolysosomes, and that degradation is occurring within them. Inhibiting actin filament rearrangement interferes with efficient particle phagocytosis but does not affect small molecule pinocytosis. We also demonstrate that cellular markers for lysolitic vesicles and reactive oxygen species (ROS) correlate with hexacorallian phagocytes. These results establish a foundation for improving our understanding of hexacorallian immune cell biology.
Highlights
Innate immunity is an important protective defense response used to recognize and destroy nonself
Using fluorescence-activated cell sorting (FACS) and microscopy, we show that a distinct population of phagocytic cells are competent to engulf bacteria and carboxylated fluorescent beads
We demonstrate that cellular markers for lysolitic vesicles and reactive oxygen species (ROS) activity are present in hexacorallian phagocytes
Summary
Innate immunity is an important protective defense response used to recognize and destroy nonself. Coral reefs are currently one of the most endangered ecosystems on the planet due to anthropogenic climate change and local human impacts [9,10,11,12,13,14] These anthropogenic impacts have caused an increase in disease outbreaks and virulence, as well as an increase in bleaching events, all culminating in negative impacts on coral immune function [10, 11, 13,14,15,16,17,18]. We know that many candidate immune genes including those involved in pathogen recognition, proteolytic response, coagulation, antimicrobial peptide precursors, and the regulation of inflammation and apoptosis are expressed in response to both coral bleaching events and disease exposure, supporting the hypothesis that innate immune responses are associated with these environmental stressors [5, 6, 8, 25, 31, 39]
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