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Echinochrome A Release by Red Spherule Cells Is an Iron-Withholding Strategy of Sea Urchin Innate Immunity

Christopher Coates Orcid Logo, Claire McCulloch, Joshua Betts, Tim Whalley

Journal of Innate Immunity, Volume: 10, Issue: 2, Pages: 119 - 130

Swansea University Author: Christopher Coates Orcid Logo

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DOI (Published version): 10.1159/000484722

Abstract

Cellular immune defences in sea urchins are shared amongst the coelomocytes – a heterogeneous population of cells residing in the coelomic fluid (blood equivalent) and tissues. The most iconic coelomocyte morphotype is the red spherule cell (or amebocyte), so named due to the abundance of cytoplasmi...

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Published in: Journal of Innate Immunity
ISSN: 1662-811X 1662-8128
Published: Karger 2018
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URI: https://cronfa.swan.ac.uk/Record/cronfa36406
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Abstract: Cellular immune defences in sea urchins are shared amongst the coelomocytes – a heterogeneous population of cells residing in the coelomic fluid (blood equivalent) and tissues. The most iconic coelomocyte morphotype is the red spherule cell (or amebocyte), so named due to the abundance of cytoplasmic vesicles containing the naphthoquinone pigment, echinochrome A. Despite their identification over a century ago, and evidence of anti-septic properties, little progress has been made in characterising the immune-competence of these cells. Upon exposure of red spherule cells from sea urchins, Paracentrotus lividus and Psammechinus miliaris, to microbial ligands, intact microbes and damage signals, we observed cellular degranulation and increased detection of cell-free echinochrome in the coelomic fluid ex vivo. Treatment of the cells with ionomycin, a calcium-specific ionophore, confirmed that an increase in intracellular levels of Ca2+ ¬is a trigger of echinochrome release. Incubating Gram-positive/negative bacteria as well as yeast with lysates of red spherule cells led to significant reductions in colony-forming units. Such antimicrobial properties were counteracted by the addition of ferric iron (Fe3+), suggesting that echinochrome acts as a primitive iron chelator in echinoid biological defences.
Item Description: C.J.C. and T.W. designed the research. All authors performedthe experiments. C.J.C. collated and analysed the data. C.J.C. preparedthis paper with input from T.W.
Keywords: coelomocytes; antimicrobial; damage response; degranulation; invertebrate immunity; Paracentrotus lividus; Psammechinus miliaris;
College: College of Science
Issue: 2
Start Page: 119
End Page: 130