Presence of anti-RNP-A and anti-RNP-C antibodies is inversely associated with renal symptoms of systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) is an autoimmune rheumatic disease characterised by the production of autoantibodies. The most common serious feature of SLE is renal involvement. An association with anti-RNP antibodies remains controversial.

Aim

To identify associations of autoantibodies and renal symptoms in a consecutive cohort of SLE patients.

Methods

Sera and clinical data from 235 consecutive SLE patients, fulfilling the ACR criteria for SLE, were collected in four centres. The presence of renal disease was defined as the presence of cellular casts in the urine, proteinuria (>0.5 g/day), or glomerulonephritis during the course of the disease. Autoantibody profiles were determined by the INNO-LIA™ ANA Update (a line immunoassay with recombinant and/or native antigens, including SmB, SmD, RNP-70, RNP-A, RNP-C, Ro52, Ro60, SSB, and ribosomal P) and anti-dsDNA antibodies by indirect immunofluorescence on Crithidia luciliae. Odds ratios (ORs) and their 95% confidence intervals (CI) were computed to determine the associations between antibodies and renal symptoms. No correction was made for multiple testing.

Results

The presence of anti-RNP-A and anti-RNP-C appeared to be protective against renal involvement (OR = 0.445, CI = 0.210–0.942 and OR = 0.484, CI = 0.243–0.964, respectively). Concerning the individual symptoms, anti-RNP-C was associated with a lower occurrence of proteinuria (OR = 0.470, CI = 0.230–6.938), cellular casts (OR = 0.324, CI = 0.150–0.696) and glomerulonephritis (OR = 0.460, CI = 0.226–0.934), whereas anti-RNP-A was only significantly associated with a lower occurrence of cellular casts (OR = 0.303, CI = 0.129–0.716). In contrast, antibodies to dsDNA were associated with a higher risk for cellular casts (OR = 2.014, CI = 1.057–3.839). We found no associations between renal symptoms and other specific antinuclear reactivities. More specifically, for anti-RNP-70 a trend was only detected for the association with the presence of cellular casts (OR = 0.411, CI = 0.153–1.106).

Conclusion

Anti-RNP-A and anti-RNP-C antibodies appear to be associated with a lower risk for renal disease.