title: An increased polymeric IgA level is not a prognostic marker for progressive IgA nephropathy.
abstract: BACKGROUND
  Elution of IgA from renal biopsies of patients with primary IgA nephropathy (IgAN) has suggested that mesangial IgA deposits are mainly multimeric in nature. This macromolecular IgA consists of dimeric and polymeric IgA and may be derived from the circulation. In children with IgAN, circulating macromolecular IgA levels correlate with bouts of macroscopic haematuria, but in adults a correlation with disease activity is less clear. Therefore, we have designed a novel method to assess the levels of polymeric IgA (pIgA) in sera from patients and controls.
  
  
  METHODS
  A novel precipitation assay using recombinant CD89 was developed to measure pIgA. Polymeric IgA levels were measured in serum samples obtained from healthy volunteers (n = 21) and patients with IgAN (n = 51). Subsequently, serum pIgA levels were correlated with clinical parameters of disease.
  
  
  RESULTS
  Serum pIgA levels were significantly increased in patients with IgAN. However, pIgA concentrations relative to total IgA were significantly lower in sera of patients with IgAN. No correlation was found between serum pIgA levels and clinical parameters of IgAN, such as decline of glomerular filtration rate, haematuria or proteinuria.
  
  
  CONCLUSIONS
  Although absolute levels of serum pIgA are increased in patients with IgAN as compared with controls, levels of pIgA relative to total serum IgA are lower. No significant correlation was found between serum concentrations of pIgA and clinical parameters of disease. These data support the notion that it is not the size alone, but the physicochemical composition of the macromolecular IgA that is the key factor leading to mesangial deposition.
authors.affiliation: Department of Nephrology, C3-P, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands. p.j.m.van_der_boog@lumc.nl
authors.forename: Paul J M
authors.initials: PJ
authors.lastname: van der Boog
authors.forename: Cees
authors.initials: C
authors.lastname: van Kooten
authors.forename: Anneke
authors.initials: A
authors.lastname: van Seggelen
authors.forename: Marko
authors.initials: M
authors.lastname: Mallat
authors.forename: Ngaisah
authors.initials: N
authors.lastname: Klar-Mohamad
authors.forename: Johan W
authors.initials: JW
authors.lastname: de Fijter
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Daha
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood*; D001704:Biopolymers / Q000097:blood; D016022:Case-Control Studies; D002850:Chromatography, Gel; D018450:Disease Progression; D005260:Female; D005919:Glomerular Filtration Rate; D005922:Glomerulonephritis, IGA / Q000097:blood / Q000150:complications / Q000503:physiopathology*; D006417:Hematuria / Q000209:etiology; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood*; D046911:Macromolecular Substances / Q000097:blood; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D011379:Prognosis; D011507:Proteinuria / Q000209:etiology
chemical_list: D015415:Biomarkers; D001704:Biopolymers; D007070:Immunoglobulin A; D046911:Macromolecular Substances; C034639:polymeric IgA