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Opsonic complement component C3 in the solitary ascidian, Halocynthia roretzi
1Department of Biochemistry, Nagoya City University Medical School, Japan. mnonaka@biol.s.u-tokyo.ac.jp
Journal of Immunology (Baltimore, Md. : 1950)
|January 14, 1999
Summary
The study identified ascidian complement C3 (AsC3), revealing a primitive innate immune system in urochordates. This ancient complement system enhances phagocytosis, predating vertebrate immunity.
Area of Science:
- Immunology
- Evolutionary Biology
- Marine Biology
Background:
- Mannose-binding lectin-associated serine proteases in Halocynthia roretzi suggest a complement system in urochordates.
- Investigating this primitive complement system is crucial for understanding early immune evolution.
Purpose of the Study:
- To elucidate the structure and function of the ascidian complement system.
- To isolate and characterize ascidian C3 (AsC3) and its role in innate immunity.
Main Methods:
- Isolation of cDNA clones for ascidian C3 (AsC3).
- Purification of AsC3 protein from ascidian body fluid.
- Analysis of AsC3 primary structure and activation site.
- Assay of opsonic activity in ascidian body fluid.
Main Results:
- Deduced AsC3 structure shows similarity to mammalian C3, including a functional thioester site.
- AsC3 activation involves cleavage of the alpha-chain near the N terminus.
- Ascidian body fluid exhibits opsonic activity enhancing phagocytosis, which is inhibited by anti-AsC3 antibodies.
Conclusions:
- The complement system played a key role in innate immunity via phagocytosis enhancement before vertebrate emergence.
- This finding predates the establishment of adaptive immunity, highlighting the ancient origins of immune defense mechanisms.