title: Caspase-activated DNase is required for maintenance of tolerance to lupus nuclear autoantigens.
abstract: OBJECTIVE
  Caspase-activated DNase (CAD) is an endonuclease that is activated by active caspase 3 during apoptosis and is responsible for degradation of chromatin into nucleosomal units. These nucleosomal units are then included in apoptotic bodies. The presence of apoptotic bodies is considered important for the generation of autoantigen in autoimmune diseases, such as systemic lupus erythematosus (SLE), that are characterized by the presence of antinuclear antibodies. The present study was carried out to determine the role of CAD in SLE and to investigate the ability of lupus autoantibodies to bind to CAD-deficient or CAD-sufficient apoptotic cells.
  
  
  METHODS
  The Sle1, Sle123, and 3H9 mouse models of SLE, in which autoimmunity is genetically predetermined, were used. To determine the role of chromatin fragmentation in SLE, CAD deficiency was introduced in these mouse models.
  
  
  RESULTS
  Deficiency of CAD resulted in increased anti-double-stranded DNA antibody titers in lupus-prone mice. Surprisingly, the absence of CAD exacerbated only genetically predetermined autoimmune responses. To further determine whether nuclear modifications are needed in order to maintain tolerance to nuclear autoantigens, we used the 3H9 mouse, an anti-DNA heavy chain knockin; in this model, the autoreactive B cells are tolerized by anergy. In accordance with findings in the CAD-mutant Sle1 and Sle123 mice, CAD-deficient 3H9 mice spontaneously generated anti-DNA antibodies. Finally, we showed that autoantibodies with specificities toward histone-DNA complexes bind more to CAD-deficient apoptotic cells than to CAD-sufficient apoptotic cells.
  
  
  CONCLUSIONS
  We propose that in mice that are genetically predisposed to lupus development, nuclear apoptotic modifications are needed to maintain tolerance. In the absence of these modifications, apoptotic chromatin is abnormally exposed, facilitating the autoimmune response.
authors: Temple University, Philadelphia, Pennsylvania 19140, USA.
authors: Neelakshi R
authors: NR
authors: Jog
authors: Lorenza
authors: L
authors: Frisoni
authors: Qin
authors: Q
authors: Shi
authors: Marc
authors: M
authors: Monestier
authors: Sairy
authors: S
authors: Hernandez
authors: Joe
authors: J
authors: Craft
authors: Eline T Luning
authors: ET
authors: Prak
authors: Roberto
authors: R
authors: Caricchio
mesh_terms: D000818:Animals; D000974:Antibodies, Antinuclear / Q000276:immunology*; D017209:Apoptosis / Q000276:immunology*; D001324:Autoantigens / Q000276:immunology*; D002467:Cell Nucleus / Q000276:immunology; D003851:Deoxyribonucleases / Q000378:metabolism*; D004195:Disease Models, Animal; D007108:Immune Tolerance / Q000276:immunology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology* / Q000378:metabolism; D051379:Mice
chemical_list: D000974:Antibodies, Antinuclear; D001324:Autoantigens; D003851:Deoxyribonucleases; C109663:caspase-activated deoxyribonuclease