Binding of high-avidity anti-β2-glycoprotein I antibodies

Objectives. We studied the influence of different binding conditions on the interaction between high- or low-avidity IgG anti-β2-glycoprotein I antibodies (anti-β2-GPI) and β2-GPI, which was either free in solution or bound to microtitre plates or nitrocellulose membranes. Methods. Sera from 30 pati...

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Bibliographic Details
Published in:Rheumatology (Oxford, England) England), 2004-11, Vol.43 (11), p.1353-1356
Main Authors: Čučnik, S., Kveder, T., Rozman, B., Božič, B.
Format: Article
Language:English
Subjects:
Affinity
Anti-β2-glycoprotein I antibodies
Antiphospholipid syndrome
Avidity
Biological and medical sciences
Diseases of the osteoarticular system
Fab fragments
Hematologic and hematopoietic diseases
Medical sciences
Platelet diseases and coagulopathies
Systemic lupus erythematosus
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Summary:Objectives. We studied the influence of different binding conditions on the interaction between high- or low-avidity IgG anti-β2-glycoprotein I antibodies (anti-β2-GPI) and β2-GPI, which was either free in solution or bound to microtitre plates or nitrocellulose membranes. Methods. Sera from 30 patients with antiphospholipid syndrome and/or systemic lupus erythematosus were selected on the basis of anti-β2-GPI positivity. Avidity of IgG anti-β2-GPI was determined by chaotropic ELISA, using increased NaCl concentration during the antibody binding. Immunodetection on nitrocellulose membrane followed reducing or non-reducing sodium dodecyl sulphate–polyacrylamide gel electrophoresis (PAGE) of β2-GPI. In converted, non-reducing PAGE, the preparation with high-affinity Fab fragments (obtained by papain digestion) was subjected to electrophoresis, while purified β2-GPI was used as the sample in immunodetection. Results. Anti-β2-GPI antibodies of high, low or heterogeneous (low and high) avidity were found in 5/30, 9/30 and 16/30 sera, respectively. The density of β2-GPI, which was 20–30 times higher on the nitrocellulose membrane than on the surface of ELISA plates, was not sufficient for the recognition of the antigen by anti-β2-GPI: 2/5 high-avidity samples reacted only with non-reduced β2-GPI, 3/9 low-avidity samples recognized only denatured and reduced β2-GPI, and 1/16 samples with heterogeneous-avidity antibodies reacted with reduced and non-reduced β2-GPI. Conclusions. Our results suggest that neither high density of the antigen nor high avidity of the antibodies (or Fab fragments) alone was sufficient for the binding of anti-β2-GPI to β2-GPI. Some conformational modifications and, consequently, exposed neo-epitopes are required for the recognition of β2-GPI by polyclonal anti-β2-GPI antibodies.
ISSN:1462-0324
1462-0332
DOI:10.1093/rheumatology/keh349