Inflammation is a process - a series of cellular changes that signal the body's response to injury or infection. It can be caused by physical agents, chemical stimuli and biologic agents (bacteria, viruses). The leukocytes are involved in the initiation and maintenance of inflammation.
Inflammation brings more leukocytes to the sight of infection. The process of leukocyte movement from the blood to the tissues through the blood vessels is known as extravasation,
