Oxidation of beta2-glycoprotein I (beta2GPI) by the hydroxyl radical alters phospholipid binding and modulates recognition by anti-beta2GPI autoantibodies.
We investigated whether beta2-glycoprotein I (beta2GPI), the key antigen in the antiphospholipid syndrome, is susceptible to oxidative modifications by the hydroxyl radical (*OH) that may influence its lipid-binding and antigenic properties. The effects on human and bovine beta2GPI of *OH free radicals generated by gamma-radiolysis of water with 137Cs were studied. Radiolytic *OH caused a dose-dependent loss of tryptophan, production of dityrosine and carbonyl groups. dimerization and/or extensive aggregation of beta2GPI. It ensued a reduction in affinity binding to cardiolipin liposomes and loss of beta2GPI-dependent autoantibody binding to immobilized cardiolipin. Patient anti-beta2GPI antibodies (n = 20) segregated into two groups based on the effect in the beta2GPI-ELISA of beta2GPI pretreatment with *OH: enhancement (group A, n = 10) or suppression (group B, n = 10) of IgG binding. The avidities of group A antibodies for fluid-phase beta2GPI were low but increased in a dose-dependent manner upon beta2GPI irradiation, in relation to protein crosslinking. Distinguishing features of group B antibodies included higher avidities for fluid-phase beta2GPI that was no longer recognized after *OH treatment, and negative anticardiolipin tests suggesting epitope location near the phospholipid binding site. The *OH scavengers thiourea and mannitol efficiently protected against all above changes. Therefore, oxidative modifications of beta2GPI via *OH attack of susceptible amino acids alter phospholipid binding, and modulate recognition by autoantibodies depending on their epitope specificities. These findings may be of clinical relevance for the generation and/or reactivity of anti-beta2GPI antibodies.
Arvieux
J
J
Laboratoire d'Immunologie, Institut de Synergie des Sciences et de la Santé, CHU Brest, France. josiane.arvieux@univ-brest.fr
Regnault
V
V
Hachulla
E
E
Darnige
L
L
Berthou
F
F
Youinou
P
P
D000818:Animals; D017152:Antibodies, Antiphospholipid / Q000276:immunology; D000915:Antibody Affinity; D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D016736:Antiphospholipid Syndrome / Q000209:etiology / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology*; D001327:Autoimmune Diseases / Q000276:immunology; D002308:Cardiolipins / Q000276:immunology / Q000378:metabolism; D002417:Cattle; D019281:Dimerization; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005720:Gamma Rays; D006023:Glycoproteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D017665:Hydroxyl Radical / Q000494:pharmacology*; D007074:Immunoglobulin G / Q000276:immunology / Q000378:metabolism; D008081:Liposomes; D008180:Lupus Erythematosus, Systemic / Q000150:complications / Q000276:immunology; D046911:Macromolecular Substances; D008353:Mannitol / Q000494:pharmacology; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000276:immunology* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013890:Thiourea / Q000494:pharmacology; D019851:Thrombophilia / Q000276:immunology; D014364:Tryptophan / Q000737:chemistry; D014867:Water; D053482:beta 2-Glycoprotein I
D017152:Antibodies, Antiphospholipid; D001323:Autoantibodies; D002308:Cardiolipins; D000939:Epitopes; D016166:Free Radical Scavengers; D006023:Glycoproteins; D007074:Immunoglobulin G; D008081:Liposomes; D046911:Macromolecular Substances; D010743:Phospholipids; D053482:beta 2-Glycoprotein I; D014867:Water; D017665:Hydroxyl Radical; D008353:Mannitol; D014364:Tryptophan; D013890:Thiourea