Pathogenic anti-beta2-glycoprotein I antibodies recognize domain I of beta2-glycoprotein I only after a conformational change.
Recently, we published the existence of 2 populations of anti-beta2-glycoprotein I (beta2- GPI) IgG antibodies. Type A antibodies recognize epitope G40-R43 in domain I of beta2- GPI and are strongly associated with thrombosis. Type B antibodies recognize other parts of beta2- GPI and are not associated with thrombosis. In this study we demonstrate that type A antibodies only recognize plasma-purified beta2- GPI when coated onto a negatively charged surface and not when coated onto a neutrally charged surface. The affinity of type B antibodies toward plasma-purified beta2- GPI was independent of the charge of the surface to which beta2- GPI was coated. Type A antibodies did not recognize plasma-purified beta2- GPI in solution, whereas they did recognize recombinant beta2- GPI both in solution and coated onto a neutrally charged plate. When the carbohydrate chains were removed from plasma-purified beta2- GPI, we found that type A antibodies did recognize the protein in solution. This supports the hypothesis that the difference in recognition of plasma-purified and recombinant beta2- GPI is caused by the difference in glycosylation and that epitope G40-R43 of plasma-purified beta2- GPI is covered by a carbohydrate chain. Type A anti-beta2-GPI antibodies can only recognize this epitope when this carbohydrate chain is displaced as a result of a conformational change. This finding has major implications both for the detection of pathogenic anti-beta2-GPI antibodies and the comprehension of the pathophysiology of the antiphospholipid syndrome.[1]References
- Pathogenic anti-beta2-glycoprotein I antibodies recognize domain I of beta2-glycoprotein I only after a conformational change. de Laat, B., Derksen, R.H., van Lummel, M., Pennings, M.T., de Groot, P.G. Blood (2006) [Pubmed]
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