Collections and ficolins: humoral lectins of the innate immune defense.
Collectins and ficolins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune systems, which recognize pathogen-associated molecular patterns. The human collectins, mannan-binding lectin (MBL) and surfactant protein A and D (SP-A and SP-D), are oligomeric proteins composed of carbohydrate-recognition domains (CRDs) attached to collagenous regions and are thus structurally similar to the ficolins, L-ficolin, M-ficolin, and H-ficolin. However, they make use of different CRD structures: C-type lectin domains for the collectins and fibrinogen-like domains for the ficolins. Upon recognition of the infectious agent, MBL and the ficolins initiate the lectin pathway of complement activation through attached serine proteases (MASPs), whereas SP-A and SP-D rely on other effector mechanisms: direct opsonization, neutralization, and agglutination. This limits the infection and concurrently orchestrates the subsequent adaptive immune response. Deficiencies of the proteins may predispose to infections or other complications, e.g., reperfusion injuries or autoimmune diseases. Structure, function, clinical implications, and phylogeny are reviewed.
Holmskov
Uffe
U
Department of Medical Biology, University of Southern Denmark, DK5000, Odeuse, Denmark. UHolmskov@health.sdu.dk
Thiel
Steffen
S
Jensenius
Jens C
JC
D000818:Animals; D001419:Bacteria / Q000276:immunology; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D037222:Collectins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D003167:Complement Activation; D005658:Fungi / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D037102:Lectins; D037601:Mannose-Binding Lectin / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D050606:Mannose-Binding Protein-Associated Serine Proteases; D051379:Mice; D008958:Models, Molecular; D010802:Phylogeny; D011110:Polymorphism, Genetic; D037662:Pulmonary Surfactant-Associated Protein A / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D037663:Pulmonary Surfactant-Associated Protein D / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D011971:Receptors, Immunologic / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D014780:Viruses / Q000276:immunology; D000097604:Ficolins
D002352:Carrier Proteins; D037222:Collectins; D037102:Lectins; D037601:Mannose-Binding Lectin; D050606:Mannose-Binding Protein-Associated Serine Proteases; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D011971:Receptors, Immunologic; D012697:Serine Endopeptidases; D000097604:Ficolins