Regulation of leukocyte adherence and migration by glycosylphosphatidyl-inositol-anchored proteins.

Leukocyte extravasation is essential for subsequent inflammation and the immune response. Extravasation can be divided into at least three steps; rolling, firm adhesion, and transendothelial migration. Although the mechanisms involved in the first two steps have been fairly well documented, the last step is complex and largely remains to be clarified. This review focuses on the possible role of GPI-anchored proteins on leukocytes in the regulation of their transendothelial migration. In addition to regulation by urokinase and its receptor, which has been regarded as the main modulator, we draw attention to a novel GPI-anchored protein (GPI-80) on human phagocytes that may be involved in regulating leukocyte adhesion and migration. The high degree of homology of GPI-80 with vanin-1, which is expressed on vascular tissues and is involved in prethymic cell homing into the thymus, raises the possibility that there is a family of molecules, including GPI-80 and vanin-1, that may be involved in leukocyte transendothelial migration. The possible role of soluble GPI-anchored proteins in this process is also discussed.