title: Serum free light chains as biomarkers for systemic lupus erythematosus disease activity.
abstract: OBJECTIVE
  To evaluate serum free light chains (FLC) as a putative biomarker of systemic lupus erythematosus (SLE) activity.
  
  
  METHODS
  Seventy-five SLE patients and 41 age- and sex-matched rheumatoid arthritis (RA) controls were enrolled. Disease activity was assessed using the Safety of Estrogens in Lupus Erythematosus: National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) definition and physician global assessments for SLE and the Disease Activity Score in 28 joints for RA. Serum FLC levels were compared against other biomarkers (IgG, C3, C4, double-stranded DNA [dsDNA] antibody). Nonparametric tests were used to compare 1) FLC and IgG in SLE versus RA and healthy controls, 2) FLC and IgG among different levels of activity in SLE, and 3) FLC in active versus nonactive RA. Correlation of FLC, C3, C4, dsDNA antibody, and IgG with the SLEDAI and modified SLEDAI (M-SLEDAI) were obtained.
  
  
  RESULTS
  FLC was higher in SLE than in RA; both were higher than referent healthy controls. Total FLC was significantly higher in subjects with greater SLE disease activity than lower/no activity. There were no significant differences in IgG, C4, or dsDNA antibody stratified by disease activity. Total FLC and C3 showed moderate to strong correlation with the SLEDAI and M-SLEDAI. In RA, no differences were seen in FLC levels for different levels of disease activity. Similar results were seen after controlling for renal function, age, and sex. In multiple linear regression, FLC significantly explained 50% variance of the SLEDAI after adjusting for renal function, age, and sex.
  
  
  CONCLUSIONS
  Serum FLC levels correlate strongly with disease activity in SLE, but not in RA. Serum FLC may be used as a biomarker of SLE disease activity.
authors.affiliation: University of Pittsburgh, Pittsburgh, Pennsylvania, USA. aggarwalr@upmc.edu
authors.forename: Rohit
authors.initials: R
authors.lastname: Aggarwal
authors.forename: Winston
authors.initials: W
authors.lastname: Sequeira
authors.forename: Rediet
authors.initials: R
authors.lastname: Kokebie
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Mikolaitis
authors.forename: Lewis
authors.initials: L
authors.lastname: Fogg
authors.forename: Alison
authors.initials: A
authors.lastname: Finnegan
authors.forename: Anna
authors.initials: A
authors.lastname: Plaas
authors.forename: Joel A
authors.initials: JA
authors.lastname: Block
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Jolly
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000175:diagnosis* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies
chemical_list: D015415:Biomarkers; D007147:Immunoglobulin Light Chains