title: APRIL levels strongly correlate with IL-17 in systemic lupus erythematosus.
abstract: BACKGROUND
  Activated self-reactive B cells play an important part in systemic lupus erythematosus (SLE). A proliferation-inducing ligand (APRIL) and B cell-activating factor (BAFF) are B-cell specific stimulators, but activate B cells through different receptors. We investigated the reciprocal association between serum APRIL (s-APRIL), serum BAFF (s-BAFF) and immunological and clinical findings in SLE patients.
  
  
  METHODS
  A cross-sectional case-control study was performed in 100 SLE patients (87% female, age 49 years, disease duration 12 years). APRIL and BAFF levels were measured by sandwich ELISA, compared with healthy controls and correlated with autoantibody, cytokine (IL-6 and IL-17) and clinical findings through nonparametric and multivariate regression analyses.
  
  
  RESULTS
  Both median s-APRIL (478 vs. 0 pg/ml, p = 0.01) and s-BAFF (1720 vs. 0.9 pg/ml, p < 0.001) were higher in SLE patients than controls. Increased s-BAFF was observed in 86% of patients, while s-APRIL was increased only in 17% (p < 0.01). S-APRIL correlated with s-BAFF in controls (p = 0.04), but not in SLE (p = 0.8). Increased s-APRIL was strongly and independently associated with IL-17 activation (p < 0.001), while increased s-BAFF levels were associated with anti-nucleosome antibody presence (p = 0.001). Disease activity and organ damage were associated with s-BAFF but not s-APRIL.
  
  
  CONCLUSIONS
  While both s-BAFF and s-APRIL levels are elevated in SLE patients, they reflect different immunologic and clinical pathways. The strong association between s-APRIL and IL-17 activation supports a role for Th17 helper cells in B cell activation in SLE.
authors: Bone and Joint Research Group, Department of Clinical Medicine, Faculty of Health Science, University of Tromsø, Norway gro.eilertsen@uit.no.
authors: G Ø
authors: GØ
authors: Eilertsen
authors: Bone and Joint Research Group, Department of Clinical Medicine, Faculty of Health Science, University of Tromsø, Norway Rheumatology Section, Division of Medicine, Royal Darwin Hospital, Darwin, NT, Australia.
authors: J C
authors: JC
authors: Nossent
mesh_terms: D001323:Autoantibodies / Q000097:blood; D053264:B-Cell Activating Factor / Q000097:blood*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007155:Immunologic Factors / Q000627:therapeutic use; D020381:Interleukin-17 / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000188:drug therapy / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13 / Q000097:blood*
chemical_list: D001323:Autoantibodies; D053264:B-Cell Activating Factor; D007155:Immunologic Factors; D020381:Interleukin-17; C114631:TNFSF13 protein, human; D053300:Tumor Necrosis Factor Ligand Superfamily Member 13
keywords: B-lymphocyte activating factor; a proliferation-inducing ligand; autoantibodies; cytokines; interleukin-17; systemic lupus erythematosus