title: Complexes of IgA with FcalphaRI/CD89 are not specific for primary IgA nephropathy.
abstract: BACKGROUND
  The presence of IgA together with the myeloid IgA-receptor FcalphaRI/CD89 in the circulation of patients with IgA nephropathy (IgAN) has been suggested as a specific pathogenic factor for mesangial deposition. However, in a recent study we found these complexes also in serum samples from healthy subjects. To investigate whether these circulating complexes are specific for IgAN, the levels and characteristics of IgA-CD89 complexes were analyzed in patients with IgAN and healthy controls.
  
  
  METHODS
  Specific ELISAs with different poly- and monoclonal antibodies and a sensitive dot-blot method were used to measure IgA-CD89 levels in serum and purified IgA samples obtained from healthy volunteers (N = 30) and patients with IgAN (N = 35). Fractionated samples of purified IgA were used to compare the size characteristics of the IgA-CD89 complexes.
  
  
  RESULTS
  Almost all CD89 in serum of patients with IgAN and controls was associated with high molecular weight IgA. Quantitative analysis of IgA-CD89 complexes in purified IgA revealed no significant difference between patients with IgAN and controls. No correlation was found between levels of IgA-CD89 complexes and clinical parameters associated with progressive IgAN.
  
  
  CONCLUSIONS
  CD89 in the circulation is found mainly linked to high molecular weight IgA. The presence of these complexes is not specific for IgAN. Therefore, if IgA-CD89 complexes are involved in the pathogenesis of primary IgA nephropathy, additional factors are required to explain the IgA-CD89 complex-mediated renal inflammation.
authors.affiliation: Department of Nephrology, Leiden University Medical Center, 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: Johan W
authors.initials: JW
authors.lastname: De Fijter
authors.forename: Cees
authors.initials: C
authors.lastname: Van Kooten
authors.forename: Rutger
authors.initials: R
authors.lastname: Van Der Holst
authors.forename: Anneke
authors.initials: A
authors.lastname: Van Seggelen
authors.forename: Leendert A
authors.initials: LA
authors.lastname: Van Es
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Daha
mesh_terms: D000328:Adult; D015703:Antigens, CD / Q000097:blood* / Q000302:isolation & purification; D016022:Case-Control Studies; D005591:Chemical Fractionation; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005922:Glomerulonephritis, IGA / Q000097:blood*; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood* / Q000737:chemistry / Q000302:isolation & purification; D008297:Male; D008875:Middle Aged; D008970:Molecular Weight; D011961:Receptors, Fc / Q000097:blood* / Q000302:isolation & purification
chemical_list: D015703:Antigens, CD; C036832:Fc(alpha) receptor; D007070:Immunoglobulin A; D011961:Receptors, Fc