Prolonged ischemia increases severity of rejection in skin flap allotransplantation in rats.

To investigate the relationship between ischemic time and rejection against allotransplants, vascularized cutaneous flaps from the groin of Brown Norway rats were transplanted to Lewis rats. The ischemic time was set at 1 hour and 6 hours for comparison. Cycrosporine A was used as the immunosuppressant. The results showed more severe rejection in the 6 hours ischemic time group in vivo, and in vitro examination using mixed lymphocyte reaction assay also demonstrated a greater antidonor response in 6 hours-ischemic group than that in 1 hour-group. Immunohistochemical study demonstrated more MHC class II antigen expression in 6 hours-ischemic group than in 1 hour-group. These results suggest that longer ischemic time induces more severe rejection against allo-transplanted tissue compared with the shorter one through an upregulation of MHC class II antigen. It is expected that these findings contribute to the studies for investigating the mechanism of rejection against the allo-transplants. Copyright 2009 Wiley-Liss, Inc. Microsurgery, 2010.