Clinical Significance of Anti-Ribosomal P Protein Antibodies in Patients with Lupus Nephritis

BACKGROUND: Systemic Lupus Erythematosus (SLE) is a chronic inflammatory disorder affecting multiple systems of the body. Clinical features show wide variations in patients with the different ethnic background. Renal involvement is a predictor of poor prognosis. Immunological workup is an integral part of SLE diagnostic criteria. Anti-ribosomal P Protein (anti-P) antibodies are highly specific for SLE. They may be present in Antinuclear Antibodies (ANA) negative SLE patients. Their role in Lupus Nephritis (LN) is under debate, some researchers found them associated with poor prognosis whereas others found favorable effect of these antibodies on renal disease. OBJECTIVE: In this study, we investigated frequency of anti-P antibodies and the effect of these antibodies on renal functions in the LN patients. METHODS: A total of 133 SLE patients were enrolled in this study. All patients had ANA in their sera. Anti-P antibodies along with other autoantibodies against extractable nuclear antigens (anti-Sm, anti- SS-A, anti-SS-B, anti-histones and anti-RNP) were detected by Immunoblot assay. Anti-dsDNA antibodies were detected by indirect Immunofluorescence Assay (IFA). RESULTS: We found anti-P antibodies in 10.5% LN patients. Interestingly their presence in association with anti-dsDNA was associated with improved renal functions in comparison to those who had antidsDNA antibodies in isolation (serum creatinine: 1.3 ± 0.8 mg/dl vs. 3.0 ± 3.0; P= 0.091). CONCLUSION: Anti-dsDNA antibodies are directly involved in renal pathology in SLE patients. As these antibodies are nephrotoxic, concomitant occurrence of anti-P antibodies seems to offer a shielding effect on renal functions, which was evident by normal serum creatinine levels. Therefore, anti-P antibodies may be considered as a good prognostic marker in these patients.