title: A novel autoantibody against fibronectin leucine-rich transmembrane protein 2 expressed on the endothelial cell surface identified by retroviral vector system in systemic lupus erythematosus.
abstract: BACKGROUND
  Anti-endothelial cell antibodies (AECAs) are thought to be critical for vasculitides in collagen diseases, but most were directed against molecules localized within the cell and not expressed on the cell surface. To clarify the pathogenic roles of AECAs, we constructed a retroviral vector system for identification of autoantigens expressed on the endothelial cell surface.
  
  
  METHODS
  AECA activity in sera from patients with collagen diseases was measured with flow cytometry by using human umbilical vein endothelial cells (HUVECs). A cDNA library of HUVECs was retrovirally transfected into a rat myeloma cell line, from which AECA-positive clones were sorted with flow cytometry. cDNA of the cells was analyzed to identify an autoantigen, and then the clinical characteristics and the functional significance of the autoantibody were evaluated.
  
  
  RESULTS
  Two distinct AECA-positive clones were isolated by using serum immunoglobulin G (IgG) from a patient with systemic lupus erythematosus (SLE). Both clones were identical to cDNA of fibronectin leucine-rich transmembrane protein 2 (FLRT2). HUVECs expressed FLRT2 and the prototype AECA IgG bound specifically to FLRT2-transfected cells. Anti-FLRT2 antibody activity accounted for 21.4% of AECAs in SLE. Furthermore, anti-FLRT2 antibody induced complement-dependent cytotoxicity against FLRT2-expressing cells.
  
  
  CONCLUSIONS
  We identified the membrane protein FLRT2 as a novel autoantigen of AECAs in SLE patients by using the retroviral vector system. Anti-FLRT2 antibody has the potential to induce direct endothelial cell cytotoxicity in about 10% of SLE patients and could be a novel molecular target for intervention. Identification of such a cell-surface target for AECAs may reveal a comprehensive mechanism of vascular injury in collagen diseases.
authors: Tsuyoshi
authors: T
authors: Shirai
authors: Hiroshi
authors: H
authors: Fujii
authors: Masao
authors: M
authors: Ono
authors: Kyohei
authors: K
authors: Nakamura
authors: Ryu
authors: R
authors: Watanabe
authors: Yumi
authors: Y
authors: Tajima
authors: Naruhiko
authors: N
authors: Takasawa
authors: Tomonori
authors: T
authors: Ishii
authors: Hideo
authors: H
authors: Harigae
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001323:Autoantibodies / Q000097:blood* / Q000235:genetics; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D005822:Genetic Vectors / Q000235:genetics; D057809:HEK293 Cells; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000175:diagnosis / Q000235:genetics; D008297:Male; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D008875:Middle Aged; D051381:Rats; D012190:Retroviridae / Q000235:genetics; D055815:Young Adult
chemical_list: D001323:Autoantibodies; C404491:FLRT2 protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins