The damaging potential of leukocyte activation in the microcirculation.

Traditionally leukocytes have been regarded as beneficial cells, owing to their immunologic and antimicrobial activity. Recent evidence suggests, however, an additional role of granulocytes and monocytes as mediators of cardiovascular complications, such as ischemia, reperfusion, diabetes, physiologic shock, venous ulceration, and other conditions. Granulocytes and monocytes have a large volume, and stiff cytoplasm; they have the ability to adhere to endothelium and to other substrates; and they exert several forms of cytotoxicity. Granulocytes and monocytes may be trapped in the microcirculation, may obstruct capillaries and thereby induce a no-reflow phenomenon, and may initiate organ dysfunction via oxygen free radical production and proteolytic cleavage. Few organs seem to be spared from the potential destructive actions of these cells, and novel approaches are required to interfere with leukocyte accumulation in local regions of the peripheral circulation.