title: Antibodies to ribosomal P proteins: a potential serologic marker for lupus membranous glomerulonephritis.
abstract: OBJECTIVE
  To evaluate the relevance of antibodies to ribosomal P proteins (anti-P antibodies) in discriminating histopathologic patterns of lupus nephritis.
  
  
  METHODS
  The study group comprised 81 consecutive patients with systemic lupus erythematosus who underwent renal biopsy and for whom frozen serum was available at the time of biopsy. All biopsy specimens were reviewed in a blinded manner, according to the 2004 criteria of the International Society of Nephrology and the Renal Pathology Society. Anti-P antibodies were detected by enzyme-linked immunosorbent assay (ELISA)/immunoblot analysis, and anti-double-stranded DNA (anti-dsDNA) was detected by indirect immunofluorescence/ELISA.
  
  
  RESULTS
  Anti-P antibodies were detected in 18 patients (22%). The demographic and clinical features of patients with and those without anti-P antibodies were similar. Remarkably, analyses of biopsy specimens revealed that the frequency of anti-P antibodies in patients with class V lupus nephritis was higher than the frequency among patients with other classes of renal disease (72% versus 28%; P = 0.005). Accordingly, anti-P antibody-positive patients had a higher mean (+/-SD) proteinuria level compared with anti-P antibody-negative patients (6.4 +/- 4.8 versus 4.7 +/- 3.9 gm/dl; P = 0.046). Renal function was preserved in 6 of 7 patients who had both isolated anti-P antibodies and class V lupus nephritis. In contrast, anti-dsDNA was associated with proliferative-class lupus nephritis (P = 0.050) and higher creatinine levels (P = 0.014). Furthermore, 7 of 9 patients with isolated anti-P antibodies had class V lupus nephritis, and, more importantly, 5 of these 7 patients (71%) displayed a pure membranous pattern. Conversely, a tendency toward the predominance of class V lupus nephritis (67%) with concomitant proliferative lesions was observed when anti-P antibody was associated with anti-dsDNA.
  
  
  CONCLUSIONS
  Our data introduce anti-P antibody as a novel serologic marker for membranous lupus nephritis and support the notion that the presence of isolated anti-P antibodies may discriminate patients with pure class V lupus nephritis, whereas the simultaneous presence of anti-dsDNA antibodies suggests class V disease with concomitant proliferative lesions.
authors.affiliation: School of Medicine, University of São Paulo, São Paulo, Brazil. reumato@edu.usp.br
authors.forename: Ana Patrícia
authors.initials: AP
authors.lastname: do Nascimento
authors.forename: Vilma dos Santos Trindade
authors.initials: Vdos S
authors.lastname: Viana
authors.forename: Leonardo de Abreu
authors.initials: Lde A
authors.lastname: Testagrossa
authors.forename: Elaine Pires
authors.initials: EP
authors.lastname: Leon
authors.forename: Eduardo Ferreria
authors.initials: EF
authors.lastname: Borba
authors.forename: Rui Toledo
authors.initials: RT
authors.lastname: Barros
authors.forename: Eloísa
authors.initials: E
authors.lastname: Bonfá
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D005260:Female; D015433:Glomerulonephritis, Membranous / Q000097:blood*; D006801:Humans; D008181:Lupus Nephritis / Q000097:blood*; D008297:Male; D012269:Ribosomal Proteins / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D012269:Ribosomal Proteins