IgM binding to injured tissue precedes complement activation during skeletal muscle ischemia-reperfusion.
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.
Chan
Rodney K
RK
Department of Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Ding
Grace
G
Verna
Nicola
N
Ibrahim
Shahrul
S
Oakes
Sean
S
Austen
William G
WG
Hechtman
Herbert B
HB
Moore
Francis D
FD
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
D003176:Complement C3; D007075:Immunoglobulin M