The two poles of the lymphocyte: specialized cell compartments for migration and recruitment.

Chemotaxis, the directed migration of leukocytes towards a chemoattractant gradient, is a key phenomenon in the immune response. During lymphocyte-endothelial and -extracellular matrix interactions, chemokines induce the polarization of T lymphocytes, with generation of specialized cell compartments. The chemokine receptors involved in detection of the chemoattractant gradients concentrate at the leading edge (advancing front or anterior pole) of the cell. The adhesion molecules ICAM-1, -3, CD44 and CD43 redistribute to the uropod, an appendage at the posterior pole of migrating T lymphocyte that protrudes from the contact area with endothelial or extracellular matrix substrates. Whereas chemokine receptors sense the direction of migration, the uropod is involved in the recruitment of bystander leukocytes through LFA-1/ICAM-dependent cell-cell interactions. While beta-actin concentrates preferentially at the cell's leading edge, the motor protein myosin II and a microtubule organizing center (MTOC) are packed in the uropod. The actin-binding protein moesin, which belongs to the ERM family of ezrin, radixin and moesin, redistributes to the distal portion of uropods and physically interacts with ICAM-3, CD44 and CD43, thus acting as a physical link between the membrane molecules and the actin cytoskeleton. Moreover, the moesin-ICAM-3 association correlates with the degree of cell polarity. The redistribution of the chemokine receptors and adhesion molecules to opposite poles of the cell in response to a chemoattractant gradient may guide cell migration and cell-cell interactions during lymphoid cell trafficking in immune and inflammatory responses.