title: Biosensor analysis of beta2-glycoprotein I-reactive autoantibodies: evidence for isotype-specific binding and differentiation of pathogenic from infection-induced antibodies.
abstract: BACKGROUND
  For the laboratory diagnosis of the antiphospholipid syndrome (APS) we developed a biosensor with the ability to distinguish between disease-relevant anti-beta2-glycoprotein I (beta2GPI) autoantibodies (anti-beta2GPI) and pathogen-specific beta2GPI cross-reactive antibodies that occur transiently during infections.
  
  
  METHODS
  We used a surface plasmon resonance (SPR) biosensor device. For the detection of anti-beta2GPI in serum samples, affinity-purified human beta2GPI was covalently attached to a functionalized n-alkanethiol self-assembling monolayer on the biosensor chip. After verifying the specificity of the biosensor system with a panel of monoclonal antibodies to beta2GPI, we analyzed sera from healthy donors and patients suffering from APS, systemic lupus erythematosus (SLE), syphilis, or parvovirus B19 infections. The SPR results were compared with beta2GPI-specific ELISA.
  
  
  RESULTS
  Using the SPR biosensor, we recorded antigen binding curves with response levels in the range of 50-500, resonance units (RU) for anti-beta2GPI ELISA-positive APS patient sera. The amplitudes of the antiphospholipid antibody (APL) responses in the biosensor correlated with the overall IgG and IgM anti-beta2GPI ELISA titers with a correlation coefficient of 0.87. Moreover, we observed immunoglobulin isotype-specific association and dissociation profiles for APL binding of different APS patient sera to the biosensor-immobilized beta2GPI. In contrast to APS patient samples, no significant anti-beta2GPI binding (response levels <35 RU) was observed in samples from healthy individuals or from patients suffering from SLE, syphilis, or parvovirus B19 infection.
  
  
  CONCLUSIONS
  The SPR biosensor system enables specific detection of APS-associated beta2GPI-reactive APL and differentiation from beta2GPI cross-reactive antibodies that occur frequently during acute infections. The established association/dissociation plot for anti-beta2GPI responses in APS patient sera gives additional information regarding the influence of anti-beta2GPI IgG and IgM isotype distribution.
authors: Institute of Clinical Chemistry and Pathobiochemistry, Klinikum Rechts der Isar der TU München, München, Germany.
authors: Jochen
authors: J
authors: Metzger
authors: Philipp
authors: P
authors: von Landenberg
authors: Marcus
authors: M
authors: Kehrel
authors: Alexander
authors: A
authors: Buhl
authors: Karl J
authors: KJ
authors: Lackner
authors: Peter B
authors: PB
authors: Luppa
mesh_terms: D017152:Antibodies, Antiphospholipid / Q000097:blood; D000942:Antigens, Bacterial / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D015374:Biosensing Techniques; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007132:Immunoglobulin Isotypes / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D010322:Parvoviridae Infections / Q000276:immunology*; D016732:Parvovirus B19, Human / Q000276:immunology; D011485:Protein Binding; D020349:Surface Plasmon Resonance; D013587:Syphilis / Q000276:immunology*; D014210:Treponema pallidum / Q000276:immunology; D053482:beta 2-Glycoprotein I / Q000276:immunology*
chemical_list: D017152:Antibodies, Antiphospholipid; D000942:Antigens, Bacterial; D000956:Antigens, Viral; D001323:Autoantibodies; D007132:Immunoglobulin Isotypes; D053482:beta 2-Glycoprotein I