title: Anti-chromatin and anti-C1q antibodies in systemic lupus erythematosus compared to other systemic autoimmune diseases.
abstract: OBJECTIVE
  To evaluate the prevalence, sensitivity, and specificity of anti-chromatin and anti-C1q antibodies in systemic lupus erythematosus (SLE) and lupus nephritis compared to small vessel vasculitis and other connective tissue diseases. To provide long-term follow-up data for anti-chromatin antibodies in lupus nephritis.
  
  
  METHODS
  We determined the significance of anti-nuclear antibodies (ANA), anti- double-stranded DNA (anti-dsDNA), anti-chromatin, and anti-C1q antibodies, as well as complement factors C3 and C4, in relation to disease activity in SLE patients with (n = 47; long-term follow-up data for 33 patients) and without (n = 31) biopsy-confirmed lupus nephritis, microscopic polyangiitis (n = 37), Wegener's granulomatosis (n = 66), primary Sjögren's syndrome (n = 17), limited scleroderma (CREST syndrome) (n = 6), and progressive systemic scleroderma (PSS) (n = 11).
  
  
  RESULTS
  Anti-chromatin antibodies were more specific and sensitive than anti-C1q antibodies in distinguishing SLE patients from those with other systemic autoimmune diseases [anti-chromatin: sensitivity 64.1%, specificity 99.2%, odds ratio (OR) 219.6; anti-C1q: sensitivity 50%, specificity 72.6%, OR 2.65]. Anti-C1q antibodies were present in 75% of patients with Sjögren's syndrome and 35.1% of patients with microscopic polyangiitis. Anti-chromatin antibodies could identify SLE in patients with positive ANA but negative anti-dsDNA antibodies. Persisting anti-chromatin antibodies indicated SLE disease activity, even if anti-dsDNA antibodies had become negative. In long-term follow-up, those SLE patients with negative anti-dsDNA antibodies but persisting ANA and anti-chromatin antibodies relapsed if immunosuppression had been tapered. Anti-chromatin antibodies correlated with the SLE disease activity index (SLEDAI) as a marker of disease activity.
  
  
  CONCLUSIONS
  The measurement of anti-chromatin, but not anti-C1q, antibodies in patients with systemic autoimmune diseases increases diagnostic sensitivity and specificity for SLE and assists in treatment decisions in anti-dsDNA-negative patients.
authors.affiliation: Department of Internal Medicine I (Nephrology), University Hospital of Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Braun
authors.forename: J
authors.initials: J
authors.lastname: Sis
authors.forename: R
authors.initials: R
authors.lastname: Max
authors.forename: K
authors.initials: K
authors.lastname: Mueller
authors.forename: C
authors.initials: C
authors.lastname: Fiehn
authors.forename: M
authors.initials: M
authors.lastname: Zeier
authors.forename: K
authors.initials: K
authors.lastname: Andrassy
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000974:Antibodies, Antinuclear / Q000097:blood*; D001323:Autoantibodies / Q000097:blood*; D001327:Autoimmune Diseases / Q000097:blood / Q000150:complications / Q000276:immunology*; D002843:Chromatin / Q000276:immunology*; D015922:Complement C1q / Q000276:immunology*; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000150:complications / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009393:Nephritis / Q000209:etiology / Q000276:immunology; D013997:Time Factors
chemical_list: D000974:Antibodies, Antinuclear; D001323:Autoantibodies; D002843:Chromatin; D015922:Complement C1q