Migratory functions of natural killer cells.

In numerous investigations it has been found that natural killer (NK) cells are among the cells arriving early at the site of defense. To reach the tissue sites of defense, the circulating NK cells have to penetrate through the capillary wall and actively migrate along the matrix proteins towards the tumor or infected target cells. For this process NK cells need adhesion receptors which do not anchor them but allow reversible binding. The migration capacity of NK cells is found to be higher than that of other lymphocytes. NK cells also have the ability to increase rapidly the migratory response. IL-2 and a peptide derived from ICAM-2 are potential inducers of NK cell migration. ICAM-2 is expressed on endothelium, a site where lymphocytes start migration. Also, a matrix protein, fibronectin, increases NK cell migration. This review focuses on the migratory capacity of NK cells and on the receptors which NK cells use when they migrate on different substrata.