Acute Inflammation II: Cellular Phase

The cellular phase of acute inflammation involves steps that recruit leukocytes to the injury site.

First is margination, where leukocytes move toward the vessel wall as blood flow slows and viscosity increases. This is followed by rolling, where they loosely bind and unbind to endothelial selectins.

Next, during firm adhesion, leukocyte integrins bind tightly to endothelial adhesion molecules such as ICAM-1 and VCAM-1.

Then, in diapedesis, leukocytes squeeze between endothelial cells to enter the tissue.

Inside the phagolysosome, pathogens are broken down by reactive oxygen species and proteolytic enzymes.

After completing their role, neutrophils undergo apoptosis and are normally cleared quietly by macrophages.

If clearance is delayed, their enzymes may leak into the surrounding tissue and continue the inflammatory process.

If the injurious stimulus is eliminated, anti-inflammatory signals and pro-resolving mediators restore tissue homeostasis.

Persistent or unresolved inflammation can transition into chronic inflammation.