title: Functional characterization of a ficolin-mediated complement pathway in amphioxus.
abstract: The ficolin-mediated complement pathway plays an important role in vertebrate immunity, but it is not clear whether this pathway exists in invertebrates. Here we identified homologs of ficolin pathway components from the cephalochordate amphioxus and investigated whether they had been co-opted into a functional ficolin pathway. Four of these homologs, ficolin FCN1, serine protease MASP1 and MASP3, and complement component C3, were highly expressed in mucosal tissues and gonads, and were significantly up-regulated following bacterial infection. Recombinant FCN1 could induce hemagglutination, discriminate among sugar components, and specifically recognize and aggregate several bacteria (especially gram-positive strains) without showing bactericidal activity. This suggested that FCN1 is a dedicated pattern-recognition receptor. Recombinant serine protease MASP1/3 formed complexes with recombinant FCN1 and facilitated the activation of native C3 protein in amphioxus humoral fluid, in which C3 acted as an immune effector. We conclude that amphioxus have developed a functional ficolin-complement pathway. Because ficolin pathway components have not been reported in non-chordate species, our findings supported the idea that this pathway may represent a chordate-specific innovation in the evolution of the complement system.
authors.affiliation: Department of Biochemistry, College of Life Sciences, State Key Laboratory of Biocontrol, National Engineering Research Center of South China Sea Marine Biotechnology, Sun Yat-sen University, Guangzhou 510275, People's Republic of China.
authors.forename: Huiqing
authors.initials: H
authors.lastname: Huang
authors.forename: Shengfeng
authors.initials: S
authors.lastname: Huang
authors.forename: Yingcai
authors.initials: Y
authors.lastname: Yu
authors.forename: Shaochun
authors.initials: S
authors.lastname: Yuan
authors.forename: Rui
authors.initials: R
authors.lastname: Li
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.forename: Hongchen
authors.initials: H
authors.lastname: Zhao
authors.forename: Yanhong
authors.initials: Y
authors.lastname: Yu
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Manyi
authors.initials: M
authors.lastname: Yang
authors.forename: Liqun
authors.initials: L
authors.lastname: Xu
authors.forename: Shangwu
authors.initials: S
authors.lastname: Chen
authors.forename: Anlong
authors.initials: A
authors.lastname: Xu
mesh_terms: D000818:Animals; D002816:Chordata, Nonvertebrate / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D003176:Complement C3 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D019143:Evolution, Molecular; D005786:Gene Expression Regulation / Q000502:physiology*; D006094:Gram-Positive Bacteria / Q000276:immunology*; D037102:Lectins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D009928:Organ Specificity / Q000502:physiology; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D000097604:Ficolins
chemical_list: D003176:Complement C3; D037102:Lectins; D011994:Recombinant Proteins; D000097604:Ficolins