title: Characterization of thyroglobulin-directed and polyreactive catalytic antibodies in autoimmune disease.
abstract: Polyreactive and thyroglobulin (Tg)-directed proteolytic activities present in the serum IgG of healthy controls and patients with autoimmune disease were studied by electrophoretic separation of 125I-labeled Tg reaction products and spectrofluorometric measurement of Pro-Phe-Arg-methylcoumarinamide cleavage at the Arg-methylcoumarinamide bond. A decrease of the polyreactive proteolytic activity accompanying an increase of the Tg-cleaving activity in IgG from autoimmune thyroiditis (ATh) and systemic lupus erythematosus (SLE) patients was evident. The Tg, a known target of autoimmune reactions in ATh, was cleaved at lower levels by Abs from patients with this disease than from SLE patients. The Tg-cleaving and Tg-binding activities of the autoantibody preparations were not correlated. Enhanced rates of cleavage at saturating substrate concentrations (Vmax), not increased Tg-binding affinities, were evident in IgG preparations with the greatest Tg-cleaving activity. Similarly, diminution of the polyreactive proteolytic activity in IgG from the autoimmune disease patients was due to decreased Vmax values, not decreased substrate-binding affinities. No cleavage of Tg by IgG from subjects with HIV-1 infection, or from mice hyperimmunized with an albumin-hapten conjugate was evident, suggesting that generation of Tg-cleaving Abs does not accompany V region affinity maturation in response to unrelated Ags. These observations establish Tg as a target of catalytic autoantibodies in SLE and ATh, suggest a transition from polyreactive proteolytic activity to autoantigen-directed activity in autoimmune disease, and open the possibility that combining site chemical reactivity is a factor driving the expression of catalytic activity by autoantibodies.
authors.affiliation: Department of Anesthesiology, Eppley Cancer Research Institute, University of Nebraska Medical Center, Omaha 68198, USA. spaul@mail.unmc.edu
authors.forename: S
authors.initials: S
authors.lastname: Paul
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: R
authors.initials: R
authors.lastname: Kalaga
authors.forename: J
authors.initials: J
authors.lastname: O'Dell
authors.forename: R E
authors.initials: RE
authors.lastname: Dannenbring
authors.forename: S
authors.initials: S
authors.lastname: Swindells
authors.forename: S
authors.initials: S
authors.lastname: Hinrichs
authors.forename: P
authors.initials: P
authors.lastname: Caturegli
authors.forename: N R
authors.initials: NR
authors.lastname: Rose
mesh_terms: D001323:Autoantibodies / Q000737:chemistry* / Q000378:metabolism; D001666:Binding Sites, Antibody; D002384:Catalysis; D005456:Fluorescent Dyes; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008180:Lupus Erythematosus, Systemic / Q000276:immunology* / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism; D013379:Substrate Specificity; D013954:Thyroglobulin / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D013967:Thyroiditis, Autoimmune / Q000276:immunology* / Q000378:metabolism
chemical_list: D001323:Autoantibodies; D005456:Fluorescent Dyes; D009842:Oligopeptides; C025273:prolyl-phenylalanyl-arginine-4-methylcoumaryl-7-amide; D013954:Thyroglobulin