Antibodies to the collagen-like region of C1q in sera of patients with autoimmune rheumatic diseases.
Antibodies to the collagen-like region of C1q have recently been observed in sera of patients with systemic lupus erythematosus (SLE). In this study, we documented that these antibodies were present in 47.3% of SLE patient sera, whereas they were uncommon in sera from patients with rheumatoid arthritis (2.8%) and Sjögren's syndrome (12.8%), as well as in normal sera (6.4%). Markedly elevated antibody levels (greater than 4 SD above the normal mean) were observed almost exclusively in sera of patients with SLE. Levels of antibodies to the collagen-like region correlated highly with levels of solid-phase C1q-binding IgG when analyzed by the C1q solid-phase assay for immune complexes (r = 0.87). We previously found that, after sucrose density gradient ultracentrifugation, a predominance of the solid-phase C1q-binding IgG in SLE sera sediments as monomeric IgG. These findings, together with the present data, indicate that reactivity of SLE patients' sera in the C1q solid-phase assay reflects primarily the presence of antibodies to the collagen-like region, and not the presence of immune complexes.
Wener
M H
MH
Department of Medicine, University of Washington, Seattle 98195.
Uwatoko
S
S
Mannik
M
M
D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000473:pathology; D001323:Autoantibodies / Q000032:analysis*; D001327:Autoimmune Diseases / Q000276:immunology*; D002499:Centrifugation, Density Gradient; D003094:Collagen / Q000276:immunology*; D003166:Complement Activating Enzymes / Q000276:immunology* / Q000378:metabolism; D003172:Complement C1 / Q000276:immunology* / Q000378:metabolism; D015922:Complement C1q; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007668:Kidney / Q000473:pathology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology / Q000473:pathology; D012216:Rheumatic Diseases / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000276:immunology / Q000473:pathology
D001323:Autoantibodies; D003172:Complement C1; D007074:Immunoglobulin G; D015922:Complement C1q; D003094:Collagen; D003166:Complement Activating Enzymes