The role of the carbohydrate chains in complement (C3) fixation by solid-phase-bound human IgA.
In contrast to antigen-antibody complexes containing native human IgA, solid-phase-deposited IgA activates the alternative complement pathway and binds C3b. To investigate the role of carbohydrate chains in this, various human IgA preparations were treated with neuraminidase alone or together with N-glycanase or O-glycanase, or with mixed glycosidases from the oral bacterium, Streptococcus mitis. Depletion of oligosaccharides was determined by carbohydrate analysis. Removal of sialic acid and N-linked glycan chains greatly increased the C3b-fixing properties of normal serum IgA1 and IgA2. Myeloma IgA1 and IgA2 proteins and secretory IgA had higher C3b-binding activity than normal serum IgA, and this was further increased by removal of sialic acid and N-linked glycans. Fc alpha and Fc alpha-SC fragments of myeloma and secretory IgA1, respectively, but not Fab alpha fragments, obtained by cleavage with bacterial IgA1 proteases and also free secretory component, fixed C3b by the alternative pathway.
Nikolova
E B
EB
Department of Microbiology, University of Alabama at Birmingham 35294.
Tomana
M
M
Russell
M W
MW
D003179:Complement C3b / Q000276:immunology*; D003170:Complement Pathway, Alternative / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D006026:Glycoside Hydrolases; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology*; D007071:Immunoglobulin A, Secretory / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D007136:Immunoglobulins / Q000276:immunology; D009194:Myeloma Proteins / Q000276:immunology; D009844:Oligosaccharides / Q000276:immunology*; D010447:Peptide Hydrolases; D010969:Plastics; D011134:Polysaccharides; D012794:Sialic Acids
D007070:Immunoglobulin A; D007071:Immunoglobulin A, Secretory; D007074:Immunoglobulin G; D007136:Immunoglobulins; D009194:Myeloma Proteins; D009844:Oligosaccharides; D010969:Plastics; D011134:Polysaccharides; D012794:Sialic Acids; C017551:myeloma immunoglobulins; D003179:Complement C3b; D006026:Glycoside Hydrolases; D010447:Peptide Hydrolases