Movement of cellular elements

The most important cells in acute inflammation are leukocytes. These need to pass from the blood to the site of activity across the endothelium; they do so in overlapping stages:

• margination
• adhesion
• passage across vessel wall
• chemotaxis

The type of leukocyte in transit depends on the stage of inflammation and the stimulus:

• usually, polymorphonuclear neutrophils predominate in the first 24 hours disappearing by 36 hours
• monocytes become more frequent after 24 hours and may stay at the site of inflammation for long periods
• viral infections may promote lymphocyte transit initially
• some hypersensitivity reactions promote initial movement of eosinophilic cells