Most impoant for diapedesis?

The process of leukocyte recruitment is the migration of the leukocytes through the endothelium, called transmigration or diapedesis. Several adhesion molecules present in the intercellular junctions between endothelial cells are involved in the migration of leukocytes. These molecules include a member of the immunoglobulin superfamily called PECAM-1 (platelet endothelial cell adhesion molecule) or CD31 and several junctional adhesion molecules. Neutrophils predominate in the inflammatory infiltrate during the first 6 to 24 hours, they are replaced by monocytes in 24 to 48 hours leukocytes pierce the basement membrane, probably by secreting collagenases and enter the extravascular tissue. The cells then migrate toward the chemotactic gradient created by chemokines and other chemoattractants and accumulate in the extravascular site - chemotaxis ref:- pathology, Robbins, 9th ed, page 77