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

IntroductionAnti-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.MethodsAECA 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.ResultsTwo 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.ConclusionsWe 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.

Recombinant outer membrane protein A induces a protective immune response against Escherichia coli infection in mice

“…3a), which not only indicated membrane protein immunogenicity of the purified rOmpA protein was maintained, but also that antibodies against the extracellular domain of transmembrane proteins can specifically recognize bacteria. Additionally, it was speculated that other non-extracellular domain of rOmpA may be the epitope for anti-OmpA antibody (Shirai et al 2012). However, the immunological characteristic of OmpA is yet to be further investigated.…”

Successful Use of Intensive Immunosuppressive Therapy for Treating Simultaneously Occurring Cerebral Lesions and Pulmonary Arterial Hypertension in a Patient with Systemic Lupus Erythematosus

“…Vascular endothelial cell injuries may have been involved in the pathogenesis. Antiendothelial cell antibodies (AECAs) are often detected in lupus patients and are considered to play important roles in the development of nephritis and atherosclerotic lesions related to vascular endothelial injuries (22). AECA was detected in the sera of this patient when we measured the binding activity of IgG to human umbilical vein endothelial cells (HUVECs) using flow cytometry (data not shown) (22).…”

Neural Cell Adhesion Molecules Belonging to the Family of Leucine-Rich Repeat Proteins

“…In addition, the three members of the family have been detected in several large-scale studies (Ishikawa et al 1997 ;Clark et al 2003 ;Ota et al 2004 ;Gerhard et al 2004 ;Nagase et al 2000a ;Otsuki et al 2005 ;Taylor et al 2006 ;Deloukas et al 2001 ). The proteins have been suggested to be implicated in cirrhosis, lupus, schizophrenia, and ASDs (Lesch et al 2012 ;Anney et al 2010 ;Ahmad et al 2012 ;Shirai et al 2012Shirai et al , 2013.…”

“…FLRT2 has been identifi ed as a target for anti-endothelial cell antibodies (AECAs) in patients with the autoimmune disease systemic lupus erythematosus, suggesting that the proteins are potential therapeutic drug targets for the treatment of this disease and potentially other autoimmune diseases (Shirai et al 2012(Shirai et al , 2013Renaudineau et al 2002 ).…”