IgM binding precedes complement activation during skeletal muscle ischemia-reperfusion

Abstract

Introduction: 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 (J Immunology 2002; 168:3433) and in mice deficient in complement C3 and C4 (J Exp Med 1996; 183:2343). We postulate that tissue, when ischemic, expresses neo-antigens to which pre-formed natural IgM antibodies bind, in turn producing harmful complement activation and reperfusion injury. Methods: C57Bl/6 mice were subjected to 2 hours of tourniquet-induced hind limb ischemia followed by variable periods of reperfusion. Two hours of ischemia and 3 hours 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 1h of reperfusion and increased progressively thereafter. Conclusion: 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.