Ultrastructural localization of highly variable 185/333 immune response proteins in the coelomocytes of the sea urchin, Heliocidaris erythrogramma

• Published in: Immunology and cell biology 2011-11, Vol.89 (8), p.861-869
• Main Authors: Dheilly, Nolwenn M, Birch, Debra, Nair, Sham V, Raftos, David A
• Format: Article
• Language: English
• Subjects: 185/333 proteins; Animals; Anthocidaris - immunology; Anthocidaris - metabolism; Anthocidaris - ultrastructure; Cell Membrane - immunology; coelomocytes; Cytoplasmic Vesicles - immunology; Cytoplasmic Vesicles - ultrastructure; Digestive System - immunology; Digestive System - metabolism; Intestinal Mucosa - immunology; Intestinal Mucosa - ultrastructure; intestine; invertebrate immunity; Life Sciences; Membrane Proteins - immunology; Membrane Proteins - metabolism; Phagocytes - immunology; Phagocytes - metabolism; Phagocytosis; sea urchin; transmission electron microscopy
• ISSN: 0818-9641; 1440-1711
• DOI: 10.1038/icb.2011.3

The 185/333 proteins of sea urchins represent a family of highly variable immune response molecules with unknown functions. In this study, we show that 185/333 proteins are expressed by three cell types: amoebocytes, colourless spherule cells and gut‐associated amoebocytes. A sub‐population of amoebocytes express 185/333 proteins on the membranes of vesicles emanating from the trans‐Golgi and which later fuse with the plasma membranes of the cells. The previously uncharacterized gut‐associated amoebocytes also show a high level of 185/333 protein expression on their internal vesicles and plasma membranes. Colourless spherule cells contain 185/333 proteins within large spherules (specialized intracellular vesicles). In the presence of bacteria and yeast, the ultrastucture of colourless spherule cells changes and 185/333 proteins disappear. In contrast, 185/333 proteins were not found in the phagosomes of coelomocytes. The 185/333‐positive gut amoebocytes were often associated with anuclear bodies, which appeared to incorporate material of microbial origin that was surrounded by 185/333 proteins. The association between 185/333 proteins on gut amoebocytes and anuclear bodies suggests that these proteins may be involved in the phagocytosis of microbes in the gut epithelium.