title: Anti-class a scavenger receptor autoantibodies from systemic lupus erythematosus patients impair phagocytic clearance of apoptotic cells by macrophages in vitro.
abstract: BACKGROUND
  Inadequate clearance of apoptotic cells by macrophages is one of the reasons for the breakdown of self-tolerance. Class A scavenger receptors, macrophage receptor with collagenous structure (MARCO) and scavenger receptor A (SR-A), which are expressed on macrophages, play important roles in the uptake of apoptotic cells. A previous study reported the presence of the anti-MARCO antibody in lupus-prone mice and systemic lupus erythematosus (SLE) patients. The purpose of this study was to investigate the prevalence of anti-class A scavenger receptor antibodies in patients with various autoimmune diseases, in particular SLE, and the functional implication of those autoantibodies in the phagocytic clearance of apoptotic cells by macrophages.
  
  
  METHODS
  Purified recombinant scavenger receptor cysteine-rich (SRCR) polypeptide (ligand-binding domain of MARCO) and recombinant SR-A were used as antigens. By using enzyme-linked immunosorbent assay, the anti-SRCR and anti-SR-A antibodies were detected in the sera of untreated patients with SLE (n = 65), rheumatoid arthritis (n = 65), primary Sjögren syndrome (n = 25), and healthy blood donors (n = 85). The effect of IgG purified from SLE patients or healthy controls on the phagocytosis of apoptotic cells by macrophages was measured by the flow cytometry assay.
  
  
  RESULTS
  Anti-SRCR antibodies were present in patients with SLE (18.5%) and rheumatoid arthritis (3.1%), but not in those with primary Sjögren syndrome. Anti-SR-A antibodies were present in patients with SLE (33.8%), rheumatoid arthritis (13.8%), and primary Sjögren syndrome (12.0%). IgG from SLE patients positive for anti-SRCR or anti-SR-A antibodies showed a higher inhibition rate on binding of apoptotic cells to macrophages than IgG from healthy controls (both P < 0.05). IgG from SLE patients positive for both anti-SRCR and anti-SR-A antibodies showed a significantly higher inhibition rate on ingestion of apoptotic by macrophages than IgG from healthy controls (P < 0.05).
  
  
  CONCLUSIONS
  Our results indicated that autoantibodies to class A scavenger receptors might contribute to the breakdown of self-tolerance by impairing the clearance of apoptotic debris and play a role in the pathogenesis of autoimmune disease, especially in SLE.
authors.affiliation: Department of Rheumatology, Renji Hospital, Shanghai Jiaotong University School of Medicine, 145 Shan Dong Middle Road, Shanghai 200001, PR China.
authors.forename: Xiao-wei
authors.initials: XW
authors.lastname: Chen
authors.forename: Yan
authors.initials: Y
authors.lastname: Shen
authors.forename: Chuan-yin
authors.initials: CY
authors.lastname: Sun
authors.forename: Feng-xia
authors.initials: FX
authors.lastname: Wu
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Cheng-de
authors.initials: CD
authors.lastname: Yang
mesh_terms: D000328:Adult; D017209:Apoptosis / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology; D002469:Cell Separation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000276:immunology*; D008264:Macrophages / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D010587:Phagocytosis / Q000276:immunology*; D011971:Receptors, Immunologic / Q000276:immunology; D051117:Scavenger Receptors, Class A / Q000276:immunology
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; C490460:MARCO protein, human; D011971:Receptors, Immunologic; D051117:Scavenger Receptors, Class A