title: Investigations on the pattern recognition molecule M-ficolin: quantitative aspects of bacterial binding and leukocyte association.
abstract: M-ficolin is a PRM of the innate immune system, found in serum and associated with leukocytes. We used the soluble form to study specificity toward Gram-positive bacteria and characterized and quantified cell-associated M-ficolin. The binding of M-ficolin to capsulated and noncapsulated strains of Streptococcus agalactiae (GBS) and Staphylococcus aureus was investigated. We did not observe binding of M-ficolin to any of 13 serotypes of S. aureus. Dose-dependent binding of M-ficolin was demonstrated for all of the capsulated GBS strains. The binding was abolished by prior treatment of the bacteria with sialidase, indicating that sialic acid is the ligand for M-ficolin on these bacteria. GlcNAc could inhibit the binding, suggesting that M-ficolin binds via its FBG. M-ficolin was found associated with the complement-activating enzyme in serum, and M-ficolin bound to GBS mediated activation of the complement system. M-ficolin expression on leukocytes was evaluated by flow cytometry with anti-M-ficolin mAb. Total M-ficolin of different leukocytes was quantified in detergent extracts. Monocytes and granulocytes showed similar M-ficolin surface expression, 1.1 × 10(5) and 0.7 × 10(5) M-ficolin molecules/cell, respectively. The total M-ficolin content of the cells was 1.5 × 10(6) molecules/monocyte and approximately one-third of this for granulocytes. Lymphocytes contained <1.5% of the amount estimated for monocytes, and none was revealed on the surface of lymphocytes by flow cytometry. Immunohistochemical analysis of the distribution of M-ficolin in 25 tissues revealed staining of only granulocytes and monocytes. Reported M-ficolin expression by type II pneumocytes could not be verified. We demonstrate the specific binding of M-ficolin to sialic acids in the capsule of GBS and give quantitative aspects of the cell-associated M-ficolin.
authors: Aarhus University, Wilhelm Meyers Allé 4, DK-8000 Aarhus C, Denmark.
authors: Troels R
authors: TR
authors: Kjaer
authors: Annette G
authors: AG
authors: Hansen
authors: Uffe B S
authors: UB
authors: Sørensen
authors: Ole
authors: O
authors: Nielsen
authors: Steffen
authors: S
authors: Thiel
authors: Jens C
authors: JC
authors: Jensenius
mesh_terms: D003167:Complement Activation; D006098:Granulocytes / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D037102:Lectins / Q000276:immunology / Q000378:metabolism*; D007962:Leukocytes / Q000378:metabolism*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000378:metabolism; D009000:Monocytes / Q000276:immunology / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D011485:Protein Binding; D013203:Staphylococcal Infections / Q000276:immunology / Q000378:metabolism; D013211:Staphylococcus aureus / Q000276:immunology / Q000378:metabolism*; D013290:Streptococcal Infections / Q000276:immunology / Q000378:metabolism; D013292:Streptococcus agalactiae / Q000276:immunology / Q000378:metabolism*; D000097604:Ficolins
chemical_list: D037102:Lectins; D050606:Mannose-Binding Protein-Associated Serine Proteases; D019158:N-Acetylneuraminic Acid; D000097604:Ficolins