Significance of anti-ribonucleoprotein (RNP) antibody and anti-Smith (anti-Sm) antibody among patients with SLE or MCTD

Abstract

Background The significance of anti-ribonucleoprotein (RNP) antibody and anti-Smith (anti-Sm) antibody remains unclear in patients with systemic lupus erythematosus (SLE) or mixed connective tissue disease (MCTD). Methods Thirty patients were retrospectively enrolled in this study. They were all positive for antinuclear antibody (ANA) and anti-RNP antibody, were diagnosed with SLE(n = 25) or MCTD(n = 5), and underwent renal biopsy at our hospital between January 1990 and December 2014. These 30 patients were classified into 4 groups based on their anti-dsDNA and anti-Sm status. Renal histology was classified into 3 patterns, including pure subepithelial membranous nephropathy (MN), mesangial and/or subendothelial lesions (MES), and MN combined with MES. Results Comparison between groups A [dsDNA(-)and SM(-)] and B༻dsDNA(-)and SM(+)༽ revealed that group A was with pure MN(n = 5) + MN + MES(n = 4) + MES(n = 1) and normocomplementemia, while group B was with MES + MN(n = 2) + MES(n = 5) and hypocomplementemia. Comparison between groups C༻dsDNA(+)and SM(-)༽ and D༻dsDNA(+)and SM(+)༽showed that group C was with pure MES and normocomplementemia, while group D was with MN + MES(n = 4) + pure MES(n = 3) and hypocomplementemia. Among 10 patients in group A, all 5 patients with MCTD were categorized as pure MN, while the 5 patients with SLE were MN + MES or pure MES. Conclusion Among patients showing positivity for anti-RNP antibody alone, those with MCTD seem likely to develop pure MN, while those with SLE tend to have MES as well as MN.