The diapedesis synapse: dynamic leukocyte-endothelium interactions

When leukocytes leave the circulation, they cross the vessel wall by penetrating the endothelial monolayer, a specialized step called diapedesis. They can do that in a paracellular manner, that is, through the cell-cell junctions, or in a transcellular manner, that is, through the endothelial cell body. At this point in the transendothelial migration process, the endothelium actively participates by inducing actin-rich structures that surround the transmigrating leukocyte that in some cases extend dorsally. Morphologically, these structures resemble the interaction of an antigen-presenting-cell and a T-cell, also known as the immunological synapse. In this minireview, we highlight the similarities between these two seemingly different cell-cell interactions processes and propose the term 'diapedesis synapse' to reflect the active participation of the endothelium with the leukocyte in order to finalize diapedesis and the importance of this interaction for immune cell function that surpasses the simple act of passing through a vessel wall.