After extravasation, leukocytes emigrate in the tissue towards the site of injury .it is called as

Ref Robbins 9/e p77 Chemotaxis. After extravasating from the blood, leuko- cytes move toward sites of infection or injury along a chem- ical gradient by a process called chemotaxis. Both exogenous and endogenous substances can be chemotactic for leuko- cytes, including the following: * Bacterial products, paicularly peptides with N-formyl- methionine termini * Cytokines, especially those of the chemokine family * Components of the complement system, paicularly C5 * Products of the lipoxygenase pathway of arachidonic acid (AA) metabolism, paicularly leukotriene B4 (LTB4) These mediators, which are described in more detail later, are produced in response to infections and tissue damage and during immunologic reactions. Leukocyte infiltration in all of these situations results from the actions of various combinations of mediators.