Schematic representation showing extravasation of circulating leukocytes

Physiologic mechanisms which underlie hematopoietic cell movement into extravascular tissue. A sequential multistep process, which involves margination, rolling, adherence, and diapedesis, is utilized by circulating leukocytes to migrate out of the vasculature and move directionally into areas of inflammation and infection. Each discrete step requires the actions of different adhesion molecules. Selectins primarily mediate cellular margination and rolling, while integrins and their receptors (immunoglobulin superfamily of adhesion molecules) are used for adherence to and diapedesis through endothelial cells.