Page "Signal transduction" Paragraph 24

Important differences exist between integrin-signalling in circulating blood cells and non-circulating cells such as epithelial cells ; integrins of circulating cells are normally inactive.

For example, cell membrane integrins on circulating leukocytes are maintained in an inactive state to avoid epithelial cell attachment ; they are only activated in response to stimuli such as those received at the site of an inflammatory response.

In a similar manner, integrins at the cell membrane of circulating platelets are normally kept inactive to avoid thrombosis.

Epithelial cells ( which are non-circulating ) normally have active integrins at their cell membrane, helping maintain their stable adhesion to underlying stromal cells that provide signals to maintain normal functioning.