Anti-C1q antibodies antedate patent active glomerulonephritis in patients with systemic lupus erythematosus.
BACKGROUND
Autoantibodies against C1q correlate with lupus nephritis. We compared titers of anti-C1q and anti-dsDNA in 70 systemic lupus erythematosus patients with (n = 15) or without (n = 55) subsequent biopsy-proven lupus nephritis.


METHODS
The 15 patients with subsequent lupus nephritis had anti-C1q assays during clinical flares (mean Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), 10.0 +/- 4.7; range, 3 to 22) before the diagnosis of lupus nephritis (median, 24 months; range 3 to 192). Among the 55 others, 33 patients had active lupus (mean SLEDAI, 10.3 +/- 6.2; range, 4 to 30) without renal disease during follow-up (median 13 years; range 2 to 17 years) and 22 had inactive lupus (mean SLEDAI, 0; range, 0 to 3).


RESULTS
Anti-C1q titers were elevated in 15/15 (100%) patients who subsequently developed nephritis (class IV, n = 14; class V, n = 1) and in 15/33 (45%) patients without renal disease (P < 0.001). The median anti-C1q titer differed significantly between the groups (P = 0.003). Anti-C1q titers were persistently positive at the time of glomerulonephritis diagnosis in 70% (7/10) of patients, with no difference in titers compared with pre-nephritis values (median, 147 U/ml; interquartile range (IQR), 69 to 213 versus 116 U/ml; 50 to 284, respectively). Titers decreased after 6 months' treatment with immunosuppressive drugs and corticosteroids (median, 76 U/ml; IQR, 33 to 106) but remained above normal in 6/8 (75%) patients. Anti-dsDNA antibodies were increased in 14/15 (93.3%) patients with subsequent nephritis and 24/33 (72.7%) patients without nephritis (P = ns). Anti-C1q did not correlate with anti-dsDNA or the SLEDAI in either group.


CONCLUSIONS
Anti-C1q elevation had 50% positive predictive value (15/30) and 100% (18/18) negative predictive value for subsequent class IV or V lupus nephritis.
Meyer
Olivier C
OC
Rheumatology Unit, Bichat Hospital, APHP, 75018 Paris, France. olivier.meyer@bch.aphp.fr
Nicaise-Roland
Pascale
P
Cadoudal
Nolwenn
N
Grootenboer-Mignot
Sabine
S
Palazzo
Elisabeth
E
Hayem
Gilles
G
Dieudé
Philippe
P
Chollet-Martin
Sylvie
S
D000293:Adolescent; D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000096:biosynthesis* / Q000097:blood; D015415:Biomarkers / Q000097:blood; D015922:Complement C1q / Q000276:immunology*; D005260:Female; D005500:Follow-Up Studies; D005921:Glomerulonephritis / Q000175:diagnosis / Q000209:etiology / Q000276:immunology*; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000150:complications / Q000175:diagnosis / Q000276:immunology*; D008181:Lupus Nephritis / Q000145:classification / Q000175:diagnosis / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D055815:Young Adult
D001323:Autoantibodies; D015415:Biomarkers; D015922:Complement C1q