Related Experiment Videos
The role of the carbohydrate chains in complement (C3) fixation by solid-phase-bound human IgA
E B Nikolova1, M Tomana, M W Russell
1Department of Microbiology, University of Alabama at Birmingham 35294.
Immunology
|June 1, 1994
Summary
Solid-phase immunoglobulin A (IgA) activates the alternative complement pathway. Removing carbohydrate chains, like sialic acid and N-linked glycans, significantly boosts IgA
Area of Science:
- Immunology
- Glycobiology
- Complement System
Background:
- Native immunoglobulin A (IgA) in antigen-antibody complexes does not activate the alternative complement pathway.
- Solid-phase deposited IgA, however, can activate this pathway and bind C3b.
Purpose of the Study:
- To investigate the role of carbohydrate chains in IgA's activation of the alternative complement pathway.
- To determine how glycosylation affects IgA's C3b-binding properties.
Main Methods:
- Treatment of human IgA preparations with various glycosidases (neuraminidase, N-glycanase, O-glycanase, Streptococcus mitis glycosidases).
- Carbohydrate analysis to determine oligosaccharide depletion.
- Assessing C3b-fixing properties and C3b-binding activity of treated IgA.
Main Results:
- Removal of sialic acid and N-linked glycans significantly enhanced C3b-fixing properties of normal serum IgA1 and IgA2.
- Myeloma IgA and secretory IgA exhibited higher C3b-binding activity than normal serum IgA, further increased by glycan removal.
- Fc alpha and Fc alpha-SC fragments, but not Fab alpha fragments, fixed C3b via the alternative pathway.
Conclusions:
- Carbohydrate chains, particularly sialic acid and N-linked glycans, play a crucial role in modulating IgA's interaction with the alternative complement pathway.
- Glycosylation state significantly influences the C3b-binding capacity of IgA, with deglycosylation promoting complement activation.
- Specific IgA fragments (Fc alpha, Fc alpha-SC) are involved in C3b fixation.