Characterization of thyroglobulin-directed and polyreactive catalytic antibodies in autoimmune disease.
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.
Paul
S
S
Department of Anesthesiology, Eppley Cancer Research Institute, University of Nebraska Medical Center, Omaha 68198, USA. spaul@mail.unmc.edu
Li
L
L
Kalaga
R
R
O'Dell
J
J
Dannenbring
R E
RE
Swindells
S
S
Hinrichs
S
S
Caturegli
P
P
Rose
N R
NR
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
D001323:Autoantibodies; D005456:Fluorescent Dyes; D009842:Oligopeptides; C025273:prolyl-phenylalanyl-arginine-4-methylcoumaryl-7-amide; D013954:Thyroglobulin