title: Erythrocyte C4d and complement receptor 1 in systemic lupus erythematosus.
abstract: OBJECTIVE
  Complement activation and ineffective clearance of complement-bearing immune complexes via erythrocytes contribute to the pathogenesis of systemic lupus erythematosus (SLE). Abnormally high levels of erythrocyte C4d and low levels of complement receptor 1 (CD35) have been reported in SLE and might have diagnostic utility. We investigated whether erythrocyte C4d and complement receptor 1 were specific for SLE and whether there was any association with disease activity.
  
  
  METHODS
  Expression of complement receptor 1 (CD35) and complement protein C4d on erythrocytes was measured by indirect immunofluorescence and flow cytometry on the same day as the blood draw, in patients with SLE, patients with rheumatic disease, and in normal controls.
  
  
  RESULTS
  Within the SLE population, there was no association with disease activity measured by the physician's global assessment or SELENA SLE Disease Activity Index, nor with past or current lupus nephritis. Assays were not specific for SLE, with higher levels also seen in antiphospholipid syndrome.
  
  
  CONCLUSIONS
  Overlap of erythrocyte C4d and CD35 between SLE and other rheumatic diseases limits their utility as diagnostic tests. However, longitudinal investigation of these assays is warranted, especially given the higher levels in some patients with primary antiphospholipid syndrome.
authors: Mount Sinai Medical Center, New York, New York, USA.
authors: Vandana
authors: V
authors: Singh
authors: James A
authors: JA
authors: Mahoney
authors: Michelle
authors: M
authors: Petri
mesh_terms: D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D015935:Complement C4b; D004912:Erythrocytes / Q000276:immunology*; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood*; D017463:Receptors, Complement 3b / Q000097:blood*; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; C509991:CR1 protein, human; D010446:Peptide Fragments; D017463:Receptors, Complement 3b; D015935:Complement C4b; C032261:complement C4d