title: Opsonic complement system of the solitary ascidian, Halocynthia roretzi.
abstract: To elucidate the molecular architecture and function of the possibly primitive complement system of the solitary ascidian. Halochynthia roretzi, cDNA clones for the third component (C3) and mannose-binding lectin (MBL)-associated serine protease (MASP) were isolated from the hepatopancreas cDNA library. The deduced primary structure of ascidian C3 (AsC3) shows overall similarity to mammalian C3 including a typical thioester site. Two distinct ascidian MASPs, termed AsMASPa and AsMASPb, have the same domain structure as mammalian Clr/ Cls/MASP-1/MASP-2. Both of them show a closer similarity to mammalian MASP-1 than to mammalian Clr/Cls/ MASP-2. Ascidian body fluid contains an opsonic activity which enhances phagocytosis of yeast by ascidian blood cells, and an antibody against AsC3 inhibits this opsonic activity. These results indicate that the lectin-dependent, opsonic complement system was present prior to the emergence of the vertebrates and well ahead of the establishment of adaptive immunity.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan. mnonaka@biol.s.u-tokyo.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Nonaka
authors.forename: K
authors.initials: K
authors.lastname: Azumi
mesh_terms: D000818:Animals; D003001:Cloning, Molecular; D015923:Complement C1r / Q000235:genetics; D003173:Complement C1s / Q000235:genetics; D015932:Complement C3c / Q000737:chemistry / Q000235:genetics*; D007113:Immunity, Innate; D050606:Mannose-Binding Protein-Associated Serine Proteases; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis / Q000276:immunology; D016133:Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics*; D014561:Urochordata / Q000201:enzymology / Q000235:genetics / Q000276:immunology*
chemical_list: D009895:Opsonin Proteins; D015932:Complement C3c; D050606:Mannose-Binding Protein-Associated Serine Proteases; D012697:Serine Endopeptidases; D015923:Complement C1r; D003173:Complement C1s