<P> Extravasation is regulated by the background cytokine environment produced by the inflammatory response, and is independent of specific cellular antigens . Cytokines released in the initial immune response induce vasodilation and lower the electrical charge along the vessel's surface . Blood flow is slowed, facilitating intermolecular binding . </P> <Ul> <Li> IL - 1 activates resident lymphocytes and vascular endothelia </Li> <Li> TNFα increases vascular permeability and activates vascular endothelia </Li> <Li> CXCL8 (IL - 8) forms a chemotactic gradient that directs leukocytes towards site of tissue injury / infection (CCL2 has a similar function to CXCL8, inducing monocyte extravasation and development into macrophages); also activates leukocyte integrins </Li> </Ul> <Li> IL - 1 activates resident lymphocytes and vascular endothelia </Li> <Li> TNFα increases vascular permeability and activates vascular endothelia </Li>

Diapedesis is the squeezing of a cell through the blood vessel wall