title: IgM binding to injured tissue precedes complement activation during skeletal muscle ischemia-reperfusion.
abstract: BACKGROUND
  Skeletal muscle reperfusion injury is mediated by IgM natural antibodies and by complement activation, as shown by the attenuation of reperfusion injury seen in mice with no natural IgM [] and in mice deficient in complement C3 and C4 []. We postulate that tissue, when ischemic, expresses neoantigens to which preformed natural IgM antibodies bind, in turn producing harmful complement activation and reperfusion injury.
  
  
  METHODS
  C57Bl/6 mice were subjected to 2 h of tourniquet-induced hind limb ischemia followed by variable periods of reperfusion. Two hours of ischemia and 3 h of reperfusion produced severe muscle necrosis and edema. Deposition of IgM and C3 in tissue was assessed using immunohistochemistry on both frozen and Formalin-fixed tissue samples.
  
  
  RESULTS
  IgM binding to the endothelium and muscle bundles of the hind limb began during the ischemic period and continued throughout reperfusion up to 6 h. C3 deposition was not present during ischemia and, in contrast, began to appear at 1 h of reperfusion and increased progressively thereafter.
  
  
  CONCLUSIONS
  These data demonstrate that IgM binding to ischemic tissues precedes the damaging complement activation by a significant period of time. This has important therapeutic implications when considering anti-inflammatory therapy for reperfusion injury.
authors.affiliation: Department of Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Rodney K
authors.initials: RK
authors.lastname: Chan
authors.forename: Grace
authors.initials: G
authors.lastname: Ding
authors.forename: Nicola
authors.initials: N
authors.lastname: Verna
authors.forename: Shahrul
authors.initials: S
authors.lastname: Ibrahim
authors.forename: Sean
authors.initials: S
authors.lastname: Oakes
authors.forename: William G
authors.initials: WG
authors.lastname: Austen
authors.forename: Herbert B
authors.initials: HB
authors.lastname: Hechtman
authors.forename: Francis D
authors.initials: FD
authors.lastname: Moore
mesh_terms: D000818:Animals; D003167:Complement Activation; D003176:Complement C3 / Q000378:metabolism; D006614:Hindlimb; D007075:Immunoglobulin M / Q000378:metabolism*; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism* / Q000473:pathology; D015427:Reperfusion Injury / Q000097:blood / Q000378:metabolism* / Q000473:pathology*; D013194:Staining and Labeling; D013997:Time Factors
chemical_list: D003176:Complement C3; D007075:Immunoglobulin M