Page "Macrophage" Paragraph 2

When a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as the leukocyte extravasation, it undergoes a series of changes to become a macrophage.

Monocytes are attracted to a damaged site by chemical substances through chemotaxis, triggered by a range of stimuli including damaged cells, pathogens and cytokines released by macrophages already at the site.

At some sites such as the testis, macrophages have been shown to populate the organ through proliferation.