New damage may be initiated during reoxygenation by increased generation of ROS. Some of the ROS may be generated by injured cells with damaged mitochondria that cannot carry out the complete reduction of oxygen. Cellular anti-oxidant defense mechanisms may be compromised by ischemia, exacerbating the situation.  ROS generated by infiltrating leukocytes also may contribute to the damage of vulnerable injured cells. Activation of the complement system also may contribute to ischemia-reperfusion injury. Complement proteins may bind to the injured tissues, or to antibodies that are deposited in the tissues, and subsequent complement activation generates byproducts that exacerbate the cell injury and inflammation.Robin’s Textbook of pathology 10th edit Page 43-44