The sea urchin complement homologue, SpC3, functions as an opsonin

Lori A. Clow, David A. Raftos, Paul S. Gross, L. Courtney Smith*

*Corresponding author for this work

Research output: Contribution to journalArticle

67 Citations (Scopus)


The purple sea urchin Strongylocentrotus purpuratus expresses a homologue of complement component C3 (SpC3), which acts as a humoral opsonin. Significantly increased phagocytic activity was evident when yeast target cells were opsonized after incubation with coelomic fluid containing SpC3. SpC3 could be detected on the surface of yeast, and phagocytic activity could be inhibited by an anti-SpC3 antibody. This indicates that SpC3 promotes phagocytosis by physically tagging target cells for ingestion. Confocal microscopy showed that opsonized yeast were phagocytosed by a single coelomocyte type (polygonal phagocytes), presumably because these cells express SpC3 receptors. Overall, these data indicate that SpC3 is a major humoral opsonin in S. purpuratus coelomic fluid.

Original languageEnglish
Pages (from-to)2147-2155
Number of pages9
JournalJournal of Experimental Biology
Issue number12
Publication statusPublished - May 2004

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