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"Anticardiolipin" autoantibodies recognize beta 2-glycoprotein I in the absence of phospholipid. Importance of Ag density and bivalent binding.
J Immunol. 1995 Jan 15; 154(2):954-60.JI

Abstract

"Anticardiolipin" autoantibodies (aCL) bind to anionic phospholipids only in the presence of beta 2-glycoprotein I (beta 2GPI), a phospholipid-binding plasma protein. The exact role of beta 2GPI in the antigenic specificity of these autoantibodies is unclear, however. Experiments were performed to determine whether aCL recognize beta 2GPI in the absence of phospholipid or neo-Ags formed as a consequence of the beta 2GPI-phospholipid interaction. Although aCL+ IgG fractions did not bind to beta 2GPI alone in ELISAs that used standard polystyrene immunoassay plates, significant specific binding was detected when beta 2GPI was coated on gamma-irradiated ("high binding") polystyrene plates. This difference was associated with the greater density of beta 2GPI immobilized on the gamma-irradiated plates. Fab' fragments of patient IgG demonstrated little or no binding to immobilized beta 2GPI in ELISA, indicating a critical role for Ab bivalency. Inhibition studies of three aCL+ IgG fractions confirmed their specificity for beta 2GPI and demonstrated low affinity binding to fluid-phase beta 2GPI (Kd values of approximately 10(-5) M). aCL binding to beta 2GPI was not a result of phospholipid contamination of the assays, as determined by microphosphate assay and by lipid extraction of IgG and beta 2GPI preparations. In summary, these experiments indicate that IgG aCL are intrinsically low affinity Abs to beta 2GPI. Ab binding to beta 2GPI on a microtiter plate or anionic phospholipid membrane is dependent upon the marked increase in avidity provided by engagement of both Ag binding sites of a given IgG molecule. The data support the hypothesis that phospholipid-bound beta 2GPI is the physiologic target of aCL.

Authors+Show Affiliations

Division of Rheumatology and Immunology, Thurston Arthritis Research Center, University of North Carolina at Chapel Hill 27599.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

7814895

Citation

Roubey, R A., et al. ""Anticardiolipin" Autoantibodies Recognize Beta 2-glycoprotein I in the Absence of Phospholipid. Importance of Ag Density and Bivalent Binding." Journal of Immunology (Baltimore, Md. : 1950), vol. 154, no. 2, 1995, pp. 954-60.
Roubey RA, Eisenberg RA, Harper MF, et al. "Anticardiolipin" autoantibodies recognize beta 2-glycoprotein I in the absence of phospholipid. Importance of Ag density and bivalent binding. J Immunol. 1995;154(2):954-60.
Roubey, R. A., Eisenberg, R. A., Harper, M. F., & Winfield, J. B. (1995). "Anticardiolipin" autoantibodies recognize beta 2-glycoprotein I in the absence of phospholipid. Importance of Ag density and bivalent binding. Journal of Immunology (Baltimore, Md. : 1950), 154(2), 954-60.
Roubey RA, et al. "Anticardiolipin" Autoantibodies Recognize Beta 2-glycoprotein I in the Absence of Phospholipid. Importance of Ag Density and Bivalent Binding. J Immunol. 1995 Jan 15;154(2):954-60. PubMed PMID: 7814895.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - "Anticardiolipin" autoantibodies recognize beta 2-glycoprotein I in the absence of phospholipid. Importance of Ag density and bivalent binding. AU - Roubey,R A, AU - Eisenberg,R A, AU - Harper,M F, AU - Winfield,J B, PY - 1995/1/15/pubmed PY - 1995/1/15/medline PY - 1995/1/15/entrez SP - 954 EP - 60 JF - Journal of immunology (Baltimore, Md. : 1950) JO - J Immunol VL - 154 IS - 2 N2 - "Anticardiolipin" autoantibodies (aCL) bind to anionic phospholipids only in the presence of beta 2-glycoprotein I (beta 2GPI), a phospholipid-binding plasma protein. The exact role of beta 2GPI in the antigenic specificity of these autoantibodies is unclear, however. Experiments were performed to determine whether aCL recognize beta 2GPI in the absence of phospholipid or neo-Ags formed as a consequence of the beta 2GPI-phospholipid interaction. Although aCL+ IgG fractions did not bind to beta 2GPI alone in ELISAs that used standard polystyrene immunoassay plates, significant specific binding was detected when beta 2GPI was coated on gamma-irradiated ("high binding") polystyrene plates. This difference was associated with the greater density of beta 2GPI immobilized on the gamma-irradiated plates. Fab' fragments of patient IgG demonstrated little or no binding to immobilized beta 2GPI in ELISA, indicating a critical role for Ab bivalency. Inhibition studies of three aCL+ IgG fractions confirmed their specificity for beta 2GPI and demonstrated low affinity binding to fluid-phase beta 2GPI (Kd values of approximately 10(-5) M). aCL binding to beta 2GPI was not a result of phospholipid contamination of the assays, as determined by microphosphate assay and by lipid extraction of IgG and beta 2GPI preparations. In summary, these experiments indicate that IgG aCL are intrinsically low affinity Abs to beta 2GPI. Ab binding to beta 2GPI on a microtiter plate or anionic phospholipid membrane is dependent upon the marked increase in avidity provided by engagement of both Ag binding sites of a given IgG molecule. The data support the hypothesis that phospholipid-bound beta 2GPI is the physiologic target of aCL. SN - 0022-1767 UR - https://www.unboundmedicine.com/medline/citation/7814895/"Anticardiolipin"_autoantibodies_recognize_beta_2_glycoprotein_I_in_the_absence_of_phospholipid__Importance_of_Ag_density_and_bivalent_binding_ DB - PRIME DP - Unbound Medicine ER -