Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


Nitrated Nucleosome Levels in Patients with Systemic Lupus Erythematosus Associations with Ethnicity and Autoantibody Status.

Croca,  Sara, Pericleous,  Charis, Alber,  Karim, Yong,  Harry, Giles,  Ian, Isenberg,  David A., Rahman,  Anisur

Background/Purpose:

Many different autoantibodies have been described in patients with SLE and serological assays have concentrated mainly on measuring autoantibody levels. Measuring levels of modified autoantigens may also be valuable. Nucleosomes from apoptotic debris are known to play a key role in pathogenesis of SLE, especially lupus nephritis. Nitration of histones within nucleosomes may be enhanced in patients with SLE by the presence of increased serum levels of reactive nitrogen species characteristic of inflammatory states. We developed a novel assay for measuring serum nitrated nucleosome (NN) levels. Here we report on results of this assay in patients with SLE and associations with ethnicity and autoantibody profile.

Methods:

Multiple stored serum samples (mean 8 per patient) from a cohort of 49 patients with SLE were tested. The samples had been obtained over a mean (SD) follow-up period of 89 (46) months. NN levels were measured using a novel capture ELISA: serum added to a streptavidin plate pre-coated with a biotinylated anti-nitrotyrosine antibody followed by detection with a rabbit anti-histone-3 antibody and then an anti-rabbit IgG HRP conjugated antibody. OD values were converted to standard absorbance units (AU) by comparison to a positive control sample loaded on every plate. The mean absorbance value for each of the patients was calculated. Univariate analysis was used to investigate association between these levels and age, gender, ethnicity, disease duration and autoantibody status.

Results:

The assay yielded reproducible results with an intra and inter-plate coefficient of variation of <10%. The mean age of the patients was 36 years (SD 13) and 81% were female. 23 were Caucasian, 18 Afro-Caribbean (A-C) and 8 other ethnicities. 17 patients had no NN at any time-point. In the other 34 patients, NN levels varied over time (mean 32.4 AU; SD 62.2; min 0; max 270.4). Age, gender and disease duration were not associated with NN level. A-C patients had significantly higher NN than other ethnic groups (p=0.03). Anti-Sm positivity was strongly associated with higher NN levels. Mean NN was 103.5 AU in anti-Sm positive and 7.75 AU in anti-Sm negative patients (p<0.0001). The apparent effect of ethnicity may be mediated via anti-Sm positivity since A-C patients were significantly more likely than other ethnic groups to be anti-Sm positive (p=0.04) and within the A-C group, anti-Sm positive patients had significantly higher NN levels than anti-Sm negative patients (p= 0.0004). There was no relationship between NN levels and positivity for anti-La, anti-Ro, anti-RNP or antiphospholipid antibodies.

Conclusion:

NN were found in the serum of 65% of patients with SLE. Anti-Sm positivity and Afro-Caribbean ethnicity were associated with significantly higher NN levels. Studies to investigate the possible association of NN with anti-nucleosome antibodies are under way.

To cite this abstract, please use the following information:
Croca, Sara, Pericleous, Charis, Alber, Karim, Yong, Harry, Giles, Ian, Isenberg, David A., et al; Nitrated Nucleosome Levels in Patients with Systemic Lupus Erythematosus Associations with Ethnicity and Autoantibody Status. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :2279
DOI:

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