IgG naturally occurring antibodies stabilize and promote the generation of the alternative complement pathway C3 convertase.

Abstract

Normal human IgG contains naturally occurring anti-C3 antibodies (anti-C3 NAbs) that have been proposed to regulate complement amplification. Here, we report a novel procedure for anti-C3 NAb purification. Pooled human IgG was fractionated on a DEAE column prior to affinity chromatography on IgG and then on C3. Anti-C3 NAbs co-purified with anti-F(ab')2 NAbs. In a refined protocol, IgG fractions were absorbed on Fc, F(ab')2, and C3, which allowed to isolate the directly accessible NAbs and to remove IgG hinge-region-specific NAbs. Since a substantial fraction of total anti-C3 NAbs in whole IgG pre-existed as complexes, IgG that did not bind to the three affinity columns was treated with urea and the affinity chromatography repeated to collect the dissociated NAbs. The urea-accessible anti-F(ab')2 NAbs were rather pure but anti-C3 NAbs yet contained substantial amounts of anti-F(ab')2 NAbs. Anti-C3 NAbs showed up to 400-fold and anti-F(ab')2 NAbs, up to 30-fold enrichment as compared to pooled normal human IgG. Anti-C3 NAb preparations exhibited nephritic factor activity that was up to 60 times stronger than that of total IgG from a patient with membranoproliferative glomerulonephritis type 2. In addition, anti-C3 NAbs promoted C3 convertase generation, when added to the convertase precursor or during convertase assembly, suggesting a non-nephritic-factor mechanism. Factors H and I reduced the overall level of activity but had no influence on the NAb dose-response curve meaning that NAbs did not interfere with factor H binding. Convertase promoting activity during assembly correlated with the content of anti-C3 NAbs in NAb complexes. In conclusion, anti-C3 NAbs associated with framework-specific anti-idiotypic NAbs stabilize C3 convertase and promote its generation but their activity is compensated for in whole IgG.

• Authors: Emiliana Jelezarova, Hans U Lutz
• Journal: Molecular immunology (Mol Immunol) Vol. 42 Issue 11 Pg. 1393-403 (Jul 2005) ISSN: 0161-5890 [Print] England
• PMID: 15950735 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antibodies, Anti-Idiotypic
• CFH protein, human
• Complement C3
• Immunoglobulin G
• Complement Factor H
• Fibrinogen
• Complement C3-C5 Convertases

Topics

• Antibodies, Anti-Idiotypic (isolation & purification, metabolism)
• Complement C3 (antagonists & inhibitors, immunology, metabolism)
• Complement C3-C5 Convertases (biosynthesis, metabolism)
• Complement Factor H (metabolism, pharmacology)
• Complement Pathway, Alternative
• Enzyme Stability
• Fibrinogen (metabolism, pharmacology)
• Humans
• Immunity, Innate
• Immunoglobulin G (isolation & purification, metabolism)
• In Vitro Techniques