thiourea and Lupus-Erythematosus--Systemic

Topics: Animals; Autoantibodies; B-Lymphocytes; Cell Proliferation; Cell Survival; Chlamydia Infections; Female; Gene Expression Regulation; Heterocyclic Compounds, 2-Ring; Immunoglobulin Class Switching; Immunoglobulin G; Lupus Erythematosus, Systemic; Lymphocyte Activation; Mice; Mice, Inbred MRL lpr; NF-kappa B; Plasma Cells; rab GTP-Binding Proteins; rab7 GTP-Binding Proteins; T-Lymphocytes; Thiourea; Up-Regulation

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.

Topics: Animals; Antibodies, Antiphospholipid; Antibody Affinity; Antibody Specificity; Antigen-Antibody Reactions; Antiphospholipid Syndrome; Autoantibodies; Autoimmune Diseases; beta 2-Glycoprotein I; Cardiolipins; Cattle; Dimerization; Enzyme-Linked Immunosorbent Assay; Epitopes; Free Radical Scavengers; Gamma Rays; Glycoproteins; Humans; Hydroxyl Radical; Immunoglobulin G; Liposomes; Lupus Erythematosus, Systemic; Macromolecular Substances; Mannitol; Oxidation-Reduction; Phospholipids; Structure-Activity Relationship; Thiourea; Thrombophilia; Tryptophan; Water

Reactive oxygen species (ROS) are released at sites of inflammation during the respiratory burst which accompanies the phagocytic process. Using an in vitro system to simulate this process we have shown that ROS induce antigenic changes in DNA. More specifically, results of experiments using ROS scavengers have shown that hydroxyl radicals produced in close proximity to DNA-bound metal ions play a predominant role. ROS-mediated attack resulted in increased binding of anti-DNA antibodies to the denatured DNA. These changes were detected using IgG, IgA and IgM isotype binding to antibodies in systemic lupus erythematosus sera. Of these the IgA isotype was most discriminating in its detection of hydroxyl radical-induced damage.

Topics: Animals; Antibodies; Ascorbic Acid; Cattle; Deferoxamine; DNA; Epitopes; Free Radicals; Humans; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; Immune Sera; Immunoglobulin A; Immunoglobulin G; Immunoglobulin Isotypes; Immunoglobulin M; Lupus Erythematosus, Systemic; Nucleic Acid Denaturation; Oxygen; Thiourea